Gelcoat is popular as a surface coating in the fabrication and repair of fiberglass-based products and can also be used to patch existing gel coat, fiberglass repairs, and new construction and repair projects. Gelcoat is extremely durable and provides a high-quality finish to visible surfaces making it a popular solution for damages to fiberglass surfaces such as covering up blemishes, patching small holes, filling cracks, and renewing surface shine. Gelcoat is often referred to as a one-stop solution for almost all types of damages on fiberglass surfaces such as, boats, jet skis, wave runners, swimming pools, hot tubs, showers and more.
If you have a fiberglass pool then its surface is made of gelcoat, a liquid-colored resin that is applied to the pool shell. Gelcoat is the considered one of the most durable pool surfaces, typically lasting several decades, depending on maintenance, wear and tear, and the quality of the surface. Concrete pools need to be refinished about every ten years or so.
One of the more common areas of a fiberglass pool that needs to be refinished over time are the pool steps which can fade after exposure to pool chemicals, weather and UV rays. For more information please refer to our How to Gelcoat your Fiberglass Pool Steps article.
Cracks, holes, chips, and stains in showers and tubs made from fiberglass can be repaired with gelcoat. A common rule of thumb is if the hole is smaller than 1/2 inch, you should be able to make the repairs yourself; if it is a larger hole, then it may require the replacement of the surface or unit.
Fixing the damaged area requires applying two-part epoxy that hardens to the strength of the surrounding surface.
One of the most common ways to refinish a fiberglass deck is with a two-part polyurethane, as the results will provide a finish that will look as good as and should last at as long as the original gelcoat.
Re-gelcoating a Boat Fiberglass Hull
Regularly waxed gelcoat can last up to 15 years, depending on how well you take care of your boats hull and exposure to UV rays. If your hull is showing signs of damage such as cracking or is no longer retaining its gloss, and has chalky white powder on the surface, then it is time to re-gelcoat your hull. Dewaxer is perfect for dewaxing the hull and effectively cleaning up paint supplies.
Using gelcoat can be an excellent solution for repairing and renewing fiberglass-based surfaces. Gelcoat is sometimes referred to as marine paint for fiberglass, however it is not a paint, so if you are unfamiliar with applying gelcoat, please see our numerous how to articles as it can be difficult to apply and achieve optimal results for first time users. You can also contact Bottom Paint Store’s technical team from 8:30-5:00pm EST Monday through Friday.
There are many ways to repair spider cracks in boats, using our Gelcoat Repair Putty is an easy and fast way of doing it!
First, you will need to determine your spider cracks are only that, spider cracks. To do so, you will need to inspect the area for any sign of broken support. If the surface is steady and looks solid, then you have spider cracks.
In order to properly fix any spider cracks, you will have to open the cracks to fill them up correctly. This can be done by using a Dremel. Once the crack is open and it has a good size you can sand and clean the area. For cleaning, you may use acetone or soap and water.
Now, you are ready to use the Gelcoat Putty. Mix in a 1-1/2% ratio of MEK-P Catalyst into the putty and mix it properly. Use a putty knife to fill in the spider cracks. Once dry, sand the surface to a smooth finish.
Gelcoat does not fully cure without first supplementing it with a surfacing agent or wax additive sanding aid. Gelcoat may be thinned for use in a Portable Preval Sprayer with styrene monomer. You can spray it with a polyvinyl alcohol (PVA) before gelcoat reaches its gel stage (5-10 min.), or adding 1oz per quart of a wax additive sanding aid.
PVA or Partall Film #10 is a release agent that helps with removing parts from a mold or can be used as a surfacing agent when using gelcoat without a wax additive (sanding aid).
PVA is soluble in water making it easy to wash off. Applying can be achieved by spray or wiping the green liquid on with a sponge. It will foam slightly but dry to a clear, glossy shine. It can take 15-30 minutes depending on temperature.
For spraying gelcoat our FGCI brand does not recommend thinning.
If thinning is needed, the most cost effective and basic option is Styrene. Generally, you should not add more than 10% Styrene by volume. Patch Booster is an additive that will thin out gelcoat and not affect colors. This is added at 20-25% and the gelcoat will require catalyst at 2% so purchase an extra tube and omit wax (sanding aid).
Another thinning alternative is the Duratec High Gloss Additive. This is used with gelcoat for many reasons. Mixed at a 50/50 ratio this will produce a high gloss finish and will serve as a thinner for your gelcoat, that is why this is commonly used when spraying gelcoat. In addition, you’ll omit any additional sanding aid. After waiting a full 24 hours you can buff when cured, for a hi-gloss use 600 or higher grit paper and buff with Aqua Buff 2000 compound. Purchase an extra hardener as your gelcoat will need to be catalyzed at 2%.
If you are looking to remove some unwanted scratches on your boat or to bring back shine into your gelcoat, Aqua Buff is for you!
Aqua Buff is a polishing compound that we offer in two variations: Aqua Buff 1000-W and Aqua Buff 2000. It is mainly used as a way to remove heavy oxidation, sanding scratches, and swirl marks from gelcoat. There are no oils or polymers in Aqua Buff, so the surface you see is the true surface.
The Aqua Buff 1000-W is used for deep scratches and heavy oxidation. It has a blue-green color which is why is not recommended for white hulls. Use Aqua Buff 1000-F on white surfaces. Aqua Buff 1000-W removes 320 – 600 grit scratches.
Aqua Buff 2000 is used for finer scratches, swirl marks, and light oxidation. Use it to remove 1000 grit scratches and higher. Cleans and removes scratches from Fiber-Reinforced-Plastic parts, metals, and painted surfaces. It is strong enough for most uses and provides a shiny finish.
Apply a small portion of Aqua–Buff 1000-W or 2000 on the surface using a brush or microfiber cloth (stick to a small area)
Use a spray bottle to mist the surface with water. Only use about a coin-size amount of compound per square foot.
The finish of your fiberglass pool steps can fade after years of use and exposure to pool chemicals and the weather. If you notice that your pool steps are looking tacky it might be time for you to reapply gelcoat to them.
You can use Gel Coat if your pool steps currently have gelcoat or bare fiberglass for pool use. We don’t recommend the brushable gelcoat in pools because the chemicals can affect the gelcoat lifespan.
Brushable Gelcoat, often referred to as gelcoat paint, is a specially formulated product that is made to be applied like paint and eliminate the need for spray equipment. It has excellent leveling, Water/Osmosis resistance, UV light Stability, great Gloss Retention, and fantastic long-term durability and is available in a variety of colors. Here are some tips for successful brushable gelcoat application.
Applying Gelcoat by Brush or Roller – (Use a Brushable Gelcoat) When applying gelcoat by brush or roller, we recommend the Ultra Plus Brushable Gelcoat. (other Gelcoats are best applied by Spray) The Ultra Plus Brushable Gelcoat is designed for self-leveling and is a much easier application. It allows for a much smoother finish and less time finishing the gelcoat. It is easy to use for the “do it your selfers’! Choose a good pure (natural) resin-resistant bristle brush with tapered ends. Avoid brushes that are either too stiff or too soft. For most work, a 3″ or 4″ wide brush will suffice. If there is a trim color, you should have a narrow trim brush on hand. Our Brushable Gelcoat comes with MEKP hardener with every purchase, but you may need more which you can purchase as an option depending on the application, temperature, and other environmental factors. Gelcoat needs to be applied evenly. We suggest a thickness of 18-20 mils to properly cure. The thickness of the matchbook cover is approximately 18 mils. If you’re not sure how thick it is, pick up a mil gauge. This is a simple, easy way to see the thickness of your gelcoat.
Don’t add Patch Booster or Sanding Aid (wax). You don’t need to add sanding aid (wax) to Brushable gelcoat to have it dry tack free. The self-leveling technology added doesn’t require any additional products or additives.
Proper gelcoat application requires you apply your coats about 15-20 mils thick. We offer mil gauge for purchase.
Allow the gelcoat to cure overnight and then lightly sand it and buff it for an outstanding shine!
Use Acetone for your cleanup. Just like other Polyester-based products, Acetone is the best cleanup material!
The most important step: Adding the proper amount of Catalyst. We recommend 1.5%-2% Catalyst ratio. After adding the catalyst, you will want to mix for two minutes, preferably with a mechanical agitator (drill mixer). For your reference, here is the catalyst chart so you know exactly how much catalyst you need.
Tips 1 mL = 1 ccIf using wood mixing stick, place stick in resin before adding catalyst so wood doesn’t absorb catalystOnly catalyze slightly more than needed. Resin that cures still in the mixing pot is unusable.
Be sure to have a good strategy when applying your gelcoat. Once you mix and catalyze, you have about 15 minutes to apply the gelcoat before it starts getting hard or starts to “gel.” The actual working time depends on the amount of catalyst and how hot the working conditions are. Anything below 60 degrees, and your gelcoat will not cure, but as you get warmer and warmer, your working time will decrease rapidly. At 70 degrees, you get 15 minutes, but at 90 degrees, you only get 5 minutes. If you need more time to work, be sure to sit the can in some cold ice water to cool it down to 60 degrees to allow you a little more working time.
Here are some helpful tips on how to work with brushable gelcoat, especially during the warmer months.
Cooling the gelcoat, by refrigerating the product to around 70 degrees, will give you up to 15 minutes of working time.
Humidity can be another factor, so, make sure the mold and surrounding area is dry before applying your brushable gelcoat.
Make small batches of gelcoat at a time and catalyze at 1 ½ % to avoid the material from getting hotter. When spraying the gelcoat, make sure you catalyze at 2 %. If you choose to use Duratec, please note, the product must be cool as well.
If you seek to roll on the gelcoat, the product should be applied evenly at 14 mil thick.
For many “do-it-yourselfers,” applying gelcoat can be quite intimidating. It is not as simple as painting and can be somewhat difficult to work with. One of the most frustrating problems to deal with is a new application of gelcoat that refuses to harden and cure. When one of our customers has a problem with gelcoat not curing properly, it usually stems from one of the reasons below.
What Caused it?
Incorrect Surface Preparation – Gelcoat will only adhere to fiberglass, previously cured gelcoat, or polyester resin. Do not apply gelcoat to any paint or protective coating because it will not adhere. Existing paint will have to be removed.
In order to prepare the surface correctly, it must be sanded. The heavier fast-cut grits (40/80/100) are used to feather sand and ground out a routed area prior to filling. Also, they are used for the first sanding of gouges, scratches, and blisters. When sanding areas that have been filled with putty we suggest using 40 or 80 grit sandpaper, depending on how large the repair is. You should also feather the surrounding area of the gelcoat repair with 220/330. When sanding flat areas use a rubber block. Use 3M Abrasivesfor best results.
Next, clean the surface with or Acetone. All surfaces must be clean, dry, and free from grease, wax, oil, and other foreign matter. At this point, the repair is ready to spray or brush with gelcoat.
Not enough catalyst – Most gelcoat manufacturers list the amount of catalyst (MEKp) it requires on the side of the can. If you are unable to find a chart, you can use the two charts listed below. We recommend 1.5% – 2.0 % by volume. The Ideal range is 1.8% @ 77°F (approximately 12 drops per ounce of gelcoat.) If the gelcoat does not get enough catalyst it will not “kick” or begin to harden. Measurements need to be exact so you can be confident the gelcoat is mixed properly before applying it to the surface. If the measurement is off even slightly, the gelcoat could start to harden but not cure completely, leaving a tacky, non-sandable surface.
Too much catalyst – It is also possible to add too much catalyst (over catalyzing) to the mixture. This will cause the gelcoat to start curing in the can or while you are applying the gelcoat. It could happen when mixing larger batches of gelcoat since this is a chemical reaction that gets hot and cures quickly. Always mix in small batches. You should catalyze your material so that it cures as quickly as possible within your working time. Generally, mix one-pint batches. Under catalyzation slows down the curing process and causes fading and chalking in the final product. Double-check that the amount of catalyst you plan to add is correct for the amount of gelcoat you have set aside. Remember that gelcoat will react differently depending on the ambient air temperature. For warmer weather use less MEKp and for cooler weather use more MEKp to get the correct mixture. (See charts below.) It is always a good idea to keep your gelcoat at room temperature, especially prior to application. A good practice is to pour the mixed gel coat from the mixing container into another container used for application. This further assures that no uncatalyzed material is clinging to the sides of the pot.
Tips 1 mL = 1 cc If using wood mixing stick, place stick in resin before adding catalyst so the wood doesn’t absorb catalyst. Only catalyze slightly more than needed. Resin that cures still in the mixing pot is unusable.
Did not use a surfacing agent – In order to cure properly, most gelcoat require the use of a surfacing agent on the final coat. The most common type of surfacing agent is Wax Additive Sanding Aid. This wax additive seals off the surface from oxygen in the air, allowing the gelcoat to dry tack-free. The recommended ratio is 1 oz wax to 1 quart of gelcoat. The first coat of gelcoat does not need the wax since you will apply a second coat. When mixing gelcoat for the second coat, though, don’t forget to add in the wax additive. All Gelcoats from the Bottom Paint Store comes with the MEKP catalyst and wax additive sanding aid, but additional amounts can be purchased. If you don’t add a wax additive to the final coat (or only coat) of gelcoat it will not harden. This is true even if you added the correct amount of catalyst.
Ultra Plus Brushable Gelcoat by FGCI is one exception to this because it does not require a surfacing agent/ wax additive, but still requires the correct amount of catalyst. Just let it sit overnight to ensure it’s completely cured.
Not enough mils – For best results, apply the gelcoat to a wet film thickness of 25 mils. This will result in a cured film thickness of 18-22 mils. As gelcoat cures, it gives off heat in an exothermic chemical reaction. If the gelcoat is applied to thin, it will not reach the temperature needed and will not cure fully. A mil is equal to 0.001″ or one-thousandth of an inch. You can use a Wet film thickness gauge to find the thickness of your wet gelcoat. Press the edge of the gauge into the gelcoat until it touches the surface below. Look at the teeth on the gauge. The gelcoat’s current thickness is measured by noting the highest tooth with film on it and the next highest tooth with no film on it. For example, a mil gauge is labeled 10, 15, 20, 25, 30, and 35 mils. The only teeth with gelcoat on them are 10 and 15. So the gelcoat’s thickness is between 15 and 20 mils.
Can I apply more gelcoat over uncured gelcoat? No. Applying more gelcoat will not help the first layer cure. Most likely it will need to be removed and reapplied.
What can I try to get the gelcoat to cure? Allow more time. If something wasn’t exactly right, the gelcoat may just take a few days to harden. If it’s not rock-solid in a few days, though, you may have to scrape it off and reapply it.
How can I remove the uncured gelcoat? Acetone on a rag can be used to break down the gelcoat. Use a plastic putty knife to scrape the uncured gelcoat away.
Over the lifetime of any boat there will come a time when the deck needs to be renewed. You have a choice of non-skid additives, or paints that already contain a nonskid compound. A non skid boat deck helps protect the surface as well as the occupants.
Customers painting the floor of a jon boat, frequently use the Aluma Hawk aluminum paint with a non skid additive. This paint serves as a paint and primer in one for your aluminum surface.
Interdeck boat deck paint is a non-skid deck paint by Interlux and offers an excellent slip resistant finish. It contains a fine aggregate and will apply easily on substrates. Its low sheen finish prevents dazzling that can be reflected by sunlight off decks. Interdeck is also easy to apply and available in numerous colors. The tough polyurethane resin protects decks against everyday wear and tear.
Depending on your paint choices, follow the manufacturers application instructions whether applying to aluminum, fiberglass, or wood to ensure best adhesion and slip resistance.
A livewell is a tank found on many fishing boats that is used to keep bait and caught fish alive. It works by pumping fresh water from the surrounding body into the tank, as well as keeping the water aerated.
Most live wells on boats are made of fiberglass and usually coated with gelcoat. For more information on applying gelcoat see our How to Apply Gelcoat article.
In the case that your live well is aluminum you can apply Aluma Hawk, available in white, blue, grey, black, sand and jon boat green to the aluminum surface.
For most paints, in order to guarantee efficacy, the only way we recommend changing the color of paints is to mix like paints, ie. Mixing Aluma Hawk with Aluma Hawk. We do not recommend addition of “universal” tints or pigments into our products. Many customers desire an antifouling paint in a deep, dark blue and this can be achieved by mixing blue and black.
Gel coats and resins can have a tint added, no more than 1 oz per quart, which can limit the effect. Another option is to mix two gelcoat colors, such as white and red for pink.
When applying coatings in cooler temperatures it is important that you meet the minimum temperature requirements. This information can typically be found in the products technical data sheet, or on the can label.
As a general rule, coatings should be applied in good weather when air and surface temperatures are above 50°F (10°C) for most paints and 60°F (16°C) for epoxy, resin, and gelcoats . Surface temperature must be a least 50°F (10°C) above dew point. For optimum application properties, bring material to 70-80°F (21-27°C) temperature range prior to mixing and application.
Make sure to store the coatings inside to keep the temperature in the optimal range prior to application.
Do not let coatings freeze, as this may alter the chemical integrity of the products.
In warm (hot) conditions be sure to keep the coatings out of direct sunlight exposure.
Coatings such as resins and gelcoats that require MEKp to be added for curing will require more MEKp in cooler conditions, and less MEKp in warmer conditions. See the guide below, but refer to the specific coating’s technical data sheet for detailed information:
What Size Spray Tip Should I Use with my Spray Gun?
There are many different things to consider when selecting the appropriate size spray tip for each job. The amount of information on the subject can be overwhelming, so we at the Bottom Paint Store have done our best to make this step easier for you.
There are three main factors to consider when determining the size tip that will produce the best results.
First, examine the coating that will be sprayed. Put simply, heavier coatings will require a larger orifice size than lighter ones. For example, primers are usually thicker than the accompanying paint so you should use a 1.7 or 1.8 mm tip to prime most surfaces. Most painters will stay in the range of 1.2 to 2.0 mm unless the paint being applied is specialized. (See chart below.)
The next thing to consider is your project surface area. This determines the appropriate fan width that your sprayer will produce, that is, the shape in which the product will leave the gun nozzle. Airless spray guns have more control over the fan width than conventional spray guns because the coating is forced through the tip without being atomized by air. This causes the tip to have a large impact on the fan width and shape. Most boat projects consist of large surfaces and so a wide fan will increase the spray coverage and also provide the ability to spray close to the surface without too much build up. Smaller surfaces will require a small fan width to reduce overspray. This also makes it possible to spray further away from the surface without too much falloff because the fan is more focused.
Lastly, consider the spray gun that is being used. Make sure that the spray tip you plan on using will be supported by the gun. Most spray gun manufacturers will provide this information in their product overview. The Bottom Paint Store distributes ES Manufacturing Gelcoat Spray Guns. The ES G830 gun will support a range of 0.8 – 2.0 mm. The ES G100and G200gelcoat spray guns support a range of 0.8 – 7.1 mm tips. If you aren’t sure about your gun’s supported sizes, check with the gun manufacturer.
Common Spray Tip Sizes and Their Uses
Tip size (mm)
Commonly Used for
Parting Films – PVA – very fine mist
Clear Coats – super fine finishes
All Around Tip – clears, base coat, single stage paints
General Purpose – light to heavy viscosity materials
Primers – will apply primer quickly
Gel Coats and Resins – for thick resins and not paints
Typically the clear coat on a bass boat is meant to protect the metalflake. You can choose a clear paint or clear gelcoat.
Clear gelcoat is typically what bass boats use at the factory for UV protection over metalflake but gelcoat isn’t as easy to use as paint. Gelcoat typically covers 48 sq feet applied at 18 mils thick per gallon.
We are often asked if you can you gelcoat over gelcoat? If the surface is already covered with gelcoat, or if the surface is a fiberglass, or polyester resin, then you can. It is relatively easy to to apply gelcoat on top of gelcoat if you follow the instructions. If the surface is paint, then the paint would have to be removed before applying the gelcoat. It is important to remember not to completely rely on gelcoat as it you may still need to make repairs to your bass boat after applying gelcoat.
Non-skid paints can be used for various different applications and circumstances. The most common use of non-skid is on boats, or for marine use. Although that is the most common, it is used in many more conditions. Here are some other examples of how non skid paint can be used outside of the nautical setting.
The additive for gelcoat is extremely easy and adds just one extra step to the gelcoatapplication process. You simply mix the additive in with the gel coat before application and then apply. Alternative preferred application methods include using a flour sifter, powdered sugar shaker, or the punctured container itself, sprinkle the non skid into the gelcoat or paint. To use the container just punch holes in it with a nail or ice pick, overlappping the broadcasting stroke to provide a uniform pattern.
The amount you use is completely subjective and dependent on what your goal is; it is recommended to use no more than a quart of non-skid per gallon of paint. The available sizes of additive are a quart and a gallon.
When looking at a scratch in the gelcoat, you need to determine whether it is a surface scratch or a deep scratch. The reason being is that surface scratches can easily be buffed with a rubbing compoundas opposed to deep scratches which take a couple more steps. As long as the gelcoat around the deep scratch is in good condition, you will be able to use gelcoat putty , requires mixing MEKP catalyst-once mixed properly it can be worked with a putty knife for filling, or you can make one using gelcoatand an aerosil filler/thickener. Once the filler is applied, the service will be uneven so sanding and polishing will be necessary. Customers report wet sanding with 2000 grit worked well. Everything about the repair of the scratch is fairly easy to do.
For deeper gouges, you will need to purchase gelcoat in various colors. Tints are available as well if custom matching larger quantities of gelcoat or paste. The kit will contain everything you need to do the job including some tints for matching. Some find the gouge needs to be scraped deeper with a screwdriver or Dremel tool to open it into a wide V to make sure the gelcoat has a place to settle and more permanent. If you simply cover the cracks they may continue to spread. The gelcoat that exists on the boat is already bonded with the laminates that are underneath. That being said, you will have to rough the surface up a bit with sand paper in order to give the paste something to stick to. Please note that you need to clean the surface with acetone after sanding to clean any contaminates off that may interfere with the filling process.
When the damage is a larger (like a screw hole) you made need3M’s Preminum Marine Filleror3M Marine High Strength Repair Filler. These are for bonding and filling repairs above or below the waterline and can be sanded. Some customers prefer to mix some thickener (cabosil)and gelcoat to a thick consistency. Both of these products can be applied with a spreader. If coating over with gelcoat be sure to leave space (about 1/8 inch) for the gelcoat. Splash Zone epoxy is easy to use for large areas underwater for all substrates.
If the underlying problem for the hairline cracks is not handled, re-gelcoating over them will only be a temporary fix, such as a soggy core or broken support. The cracking has stemmed from a crack below the gelcoat and in the fiberglass. This is one option to repair those cracks:
Using a Dremel tool, remove the gelcoat on either edge of the crack, all the way down its length. Basically this widens the gap and reveals the fiberglass layer beneath.
Determine if there is a crack in the fiberglass. If there is, it needs to be filled with a putty containing fiberglass strands. Duraglas Fiberglass Filler is one option.
Apply Gelcoat to the area. Can be brushed, rolled (using Brushable Gelcoat) or spray applied.
Once you have the gelcoat mixed, saving the hardener for last, begin to spread over the gouge with a plastic spreader. Since the paste will shrink slightly as it dries, make sure you put a little extra paste on the “wound”. A slight bulge will be ideal after the paste is applied. As the paste will not cure completely in the air, you will need to put a plastic film over it. If your kit does not have one, shrink wrap or wax paper will work. Tape the plastic/wax paper on all sides over the paste and let dry for 24 hours.
After the 24 hours are up, remove the plastic/wax paper. Take a piece of 400 grit sandpaper accompanied with a 3M sanding block and begin to level any areas that are raised and uneven. It will help if you have a bucket of water or water hose handy to wash away the excess material as you sand. Once you have completed the sanding with the 400 grit, you will need to now use a 600 grit sandpaper to go over the repair. The reason this is being done is to eliminate any scratches the 400 grit may have put in the repair and smooth it even more. You will continue this process moving up to a 800 grit and then a 1200 grit. Occasionally you will want to dry the repair area just to get an idea of the work you have done so far. At this point you can wax and buff the repair.
A gelcoat surface is a very smooth, mirror-like finish when it is new. As gelcoat ages, it becomes porous which means the more easily it stains, the worse it looks and the harder it is to clean. Most all gelcoat can be restored, providing it is not completely worn through. Exhaust stains, like diesel, can develop on the surface of the Gel Coat. These stains can set in on the wax surface of the gel coat but the right cleaner can remove them. If the stain goes deeper, a bit of elbow grease will be needed.
Apply a fiberglass stain remover, like 3M Fiberglass Restorer and Wax, Mothers Marine Black Streak Remover, or 3M Marine Cleaner and Waxto the stained gelcoat area with a clean rag. The black/gray stains are the result of soot being deposited on your hull. It can happen when wet exhaust systems mix the exhaust gases with seawater and discharge those gases or dry exhaust systems discharging the soot directly into the atmosphere and it lands on your boat.
These liquid one-step products that combine a polish or compound with a wax remove oxidation, and protect the gelcoat in one step.
Wait 10-15 minutes. If the stain is simply laying on the surface of the Gel Coat, the stain will begin to loosen; rinse and inspect the results.
If the stain is lifting, repeat. If not, then something stronger like a more abrasive compound with a polisher may be needed; in that case a wax will be needed to restore the shine. Each time compound products are used, some of the gelcoat is removed. Use caution to use the least aggressive product that will get the job done. Frequently all that may be needed is to apply a protective coating of wax, such as 3M Ultra Performance Wax, Scotchgard Marine Wax, or Mothers Marine Synthetic Waxto help keep that shine.
Gel coat is a resin that is pigmented with color. The consistency of gel coat is very thick and is best applied with aspray gun.Metal flake is commonly used in clear gel coat for that “bass boat” look. Although it appears that the metal flakes are mixed into the base coat, they are usually mixed into the clear gel coat.
This can be applied over the colored gel coat and the metal flake is usually coated with clear gelcoat for added UV protection and to smooth the surface. The larger the metalflake, the more coats of clear gel coat it will often take to cover.
Usually it is recommended to use around 16 oz of metal flake per gallon of gel coat and personal preference plays a role as there us no magic ratio for adding flake. The typical bass boat will use 2-3 lbs of metal flake in the gel coat. Mix the gel coat inside a pail thoroughly with a paint stirrer to disperse the metal flakes. Stir the it thoroughly and frequently during application to prevent the metal flakes from settling to the bottom.
Metal flake gelcoat is best applied using a gel coat spray gunto achieve an even coating and be sure to use an appropriate nozzle tip based on flake size.
You will need to disassemble the spray gun to clean it well as the flakes can lodge into small areas.
Use the color chart below to determine how to tint your gel coat. Use the base color shown above and then add the corresponding gel coat tint (gel coat coloring agent). For smaller repairs, you should consider a gelcoat repair kit(available in 1oz and 4 oz kits) that include a gelcoat paste and the tints for custom matching. For larger amounts of gelcoat, we also have over 12 premixed colors of gel coat to choose from (available in quart and gallons). You can also use a neutral gelcoat which can be used with the coloring agents to make any custom gelcoat color.
Fiberglass is what is used as the base of the boat. These are the strands underneath the gelcoat that you typically do not see. (unless there is a gouge!) Over the fiberglass usually gelcoat is applied at the factory. If the surface is scratched gelcoat is the same color throughout; if the surface has been painted when scratched it will show what is underneath.
Need a repair?
If it is just a gouge and not penetrated all the way through the boat, then you would need to fill in the gouge with 3M premium marine filler (just one product that will work but our most popular for this use). After you have filled in the gouge and sanded it down, you would then apply the topcoat of gelcoat. (gelcoat is the top finish that you see on your entire boat.) Gelcoat is typically much thicker than a paint and is designed to protect the underlying fiberglass as well as provide a smooth shiny appearance. Be sure to leave the marine filler about 1/8″ lower than the surrounding gelcoat. This will allow you to apply enough gelcoat and be able to feather the surrounding area once your done. If you leave the marine filler flush, then once you apply the gelcoat you will have a lump on the area you are repairing (gelcoat should be thick enough or it could release from repair).
The amount that you will need is dependent on the size and number of gouges. If you have many gouges, you may consider buying a quart of gelcoat. However, the nice thing about the gelcoat repair kits is that they come with tints so that you can try to match your existing gelcoat color.
If you need to tint a quart our gallon to match see our available gelcoat tints, please note it isn’t recommended to use more than 1 oz of tint per quart or the curing of gelcoat could be effected.
What is difference between gel coat and paint?
Gelcoat is usually much thicker than paint and is engineered to protect the underlying fiberglass as well as provide a smooth shiny appearance. However, the nice thing about the gelcoat repair kits is that they come with tints so that you can try to match your existing gelcoat color. Paint is thinner and typically much easier to apply. Unlike paint, gelcoat will not adhere to existing paint, wood, metal or concrete. Gelcoat also has a limited shelf life of around 3-4 months at around 70 degrees whereas paints that are solvent-based can last up to 15 years while latex and water-based ones may last for up to 10 years.
Below you will find a detailed gel coat preparation guide on how to apply gelcoat to your boat, RV or other surface. The secret to a good finish is to apply gel coat properly. The application of gelcoat is pretty straight forward when you follow this guide.
Determine the Existing Surface: First thing you want to do is look at the surface on which you want gelcoat applied. If the surface is already coated with gelcoat, or if the surface is a fiberglass or polyester resin, then the application of gelcoat is a snap. If the surface is paint then the paint should be removed before the gelcoat is applied.
Prepping the Surface: Remove rails, cleats, louvers, snaps, striping tape, etc. Duct tape off adjacent gunwale molding, and deck fittings you are unable to remove. **NOTE** Duct tape is recommended over masking tape because it provides better protection. Remove seals from the edges of parts or fittings when doing a repair around that part or fitting. Take steps to cover and protect the rest of the boat before starting. When working on the deck or cabin, tarp off the adjacent areas. 3M and UV tapes , and masking papers are recommended.
Sanding Existing Gel Coat: You want to sand the surface to make a mechanical bond to the gel coat. Our technicians suggest the use of Dyekum Steel Blue Dye to be really thorough. Steel Blue is a dye you’re going to wipe on or you can use the blue dye spray. If you don’t see the blue dye again, you know you’ve sanded it all properly. Start by sanding the surface with 150 grit or sandpaper. The heavier fast-cut grits (40/80/100) are used to feather sand and ground out a routed area prior to filling. Also, they are used for the first sanding of gouges, dock dings, scratches, and blisters. When sanding areas that have been filled with putty we suggest using 40 or 80 grit sandpaper, depending on how large the repair is. Once the fill area is level or contoured to the desired shape, sand with 100 grit paper to remove the course scratches from 40 or 80 grit. You should also feather the surrounding area of the gel coat repair with 220/330. At this point, the repair is ready to prep and spray/brush with gel coat. Use 3M Abrasivesfor best results.
Preparing the Surface for Application: Next, you’re going to have to clean the surface. We encourage the use of Acetone, because it does not leave the residue and evaporates easily. When the surface is clean, you want to get moving fairly quickly; if the surface is sitting for some amount of time, you want to re-clean the surface. Dust and dirt particles are your enemy here, so make sure you clean the surface thoroughly. Determine whether you need one or two gel coat coats. If you change colors, it will require at least two gel coat coats. If this is going over a patch, at least 2 coats are recommended to get a uniform surface. Otherwise, there will be only one coat.
Method of Application: Next, determine if you are going to brush, roll or spray your gelcoat so you can prepare the gelcoat for application. You may either roll the gelcoat on, like paint, or spray it on, to apply the gelcoat. A Brushable Gel coat that can be applied with a brush and does not need any other additives except MEKP that is included with your Brushable Gelcoat. If you want to roll on a gelcoat, be sure to use a 1/8 “or 1⁄4” solvent-resistant nap. Be sure not to use foam rollers because they tend to leave the bubbles. If you brush on the gel coat, make sure to use a solvent-resistant brush.
Gel Coat Additives: You should also determine which additives that you will use with your gelcoat application.
Wax Additive: Add up to 4 oz of Wax Additive per gallon 1 oz per quart for tack free surface on the final coat, or if applying one coat a recommended film thickness. The Exterior Gelcoats that recommend a wax additive are included with purchase at Bottom Paint Store. (A wax additive is NOT used with Brushable Gel Coat or HI UV Clear.) You should only use a wax additive in the final application coat or if you are planning on only one coat.
Partall Film #10 PVA Surfacing Agent For Gel Coat Use this product as a surfacing agent when using Gel Coat without wax additive and typically larger spray applications. Partall Film #10 is a polyvinyl alcohol (PVA) water/alcohol solution of water-soluble, film-forming materials. This parting film is particularly recommended as a parting agent for separation between polyester or epoxy resins and various mold surfaces. It is not recommended for use with resins containing water or giving off water during cure (i.e., phenolics) or with automotive finishes, as damage may occur. Partall Film #10 will not shrink and pull away from corners or curved surfaces. After resin has dried, the film parts easily from the mold and is readily dissolved from the molded parts with water. An occasional coating of Partall Paste #2 is required on most mold surfaces before application of Partall Film #10. May be applied over gel coat as a surface cure agent. (recommended for HI UV Clear since no wax should be added)
Catalyzing Gelcoat with MEKP: All gelcoat MUST be catalyzed with MEKP to cure. This should be added after all other additives just prior to application. Gelcoat requires Methyl Ethyl Ketone Peroxide or MEKP to enable the process of hardening. It’s a very small number. We suggest 1-1/4% to 1-1/2% by volume, i.e. 13-15 cc per quart. Darker colors need a little more catalyst for the same reaction, so you can catalyze up to 2%. All Gel Coats from Bottom Paint Store come with MEKP with each gelcoat purchase. Refer to the catalyst chart located on the product page for the gelcoat you are using or follow the label guidelines. As a general rule: The catalyst level (MEKP) should not exceed 3.0% or fall below 1.2 for proper cure. Ideal range is 1.8% @ 77°F. Gel time at 1.8% MEKP is 10-17 minutes. This time element is dependent on material temperature, room temperature, humidity, air movement, and catalyst concentration. Gelcoat should not be used when temperature conditions are below 60°F, as curing may be adversely affected. Be sure to have a good strategy when applying your gelcoat. Once you mix and catalyze, you have about 15 minutes to apply the gelcoat before it starts getting hard or starts to “gel.” The actual working time depends on the amount of catalyst and how hot the working conditions are. Anything below 60 degrees, and your gelcoat will not cure, but as you get warmer and warmer, your working time will decrease rapidly. At 70 degrees, you get 15 minutes, but at 90 degrees, you only get 5 minutes. If you need more time to work, be sure to sit the can in some cold ice water to cool it down to 60 degrees to allow you a little more working time.
1 ML = 1 CC
If using wood mixing stick, place stick in resin before adding catalyst so wood doesn’t absorb catalyst
Only catalyze slightly more than needed. Resin that cures still in the mixing pot is unusable. Mix small batches at a time since too much MEKP will result in hardening of the gelcoat way too fast! Refer to the catalyst chart located on the product page for the gelcoat you are using or follow the label guidelines.
Gel Coat requires the addition of fiberglass resin hardener or catalyst (MEKP) at 1.8% by volume (77ºF) (approximately 12 drops per ounce)
Measure catalyst accurately. Under or over catalyzation retards curing and causes fading and chalking
All Gelcoats from the Bottom Paint Store come with the MEKP catalyst but additional amounts can be purchased.
Applying Gelcoat by Brush or Roller – (Use a Brushable Gelcoat) : When applying gelcoat by brush or roller, we recommend the Ultra Plus Brushable Gelcoat. (other gelcoats are best applied by spray) The Ultra Plus Brushable Gelcoat is designed to self-leveling and is much easier application. It allows for a much smoother finish and less time finishing the gelcoat. It is easy to use for the “do it yourselfers!’ Choose a good pure (natural) resin resistant bristle brush with tapered ends. Avoid brushes that are either too stiff or too soft. For most work, a 3″ or 4″ wide brush will suffice. If there is a trim color, you should have a narrow trim brush on hand. Our Brushable Gelcoat comes with MEKP hardener with every purchase, but you may need more which you can purchase as an option depending on the application, temperature and other environmental factors. Please refer the to Catalyzation chart on the Brushable Gelcoat page or on the label. Gelcoat needs to be applied evenly. We suggest a thickness of 18-20 mils to properly cure. The thickness of the matchbook cover is approximately 18 mils. If you’re not sure how thick it is, pick up a mil gauge. This is a simple, easy way to see the thickness of your gelcoat. Gelcoat needs to be applied evenly. We suggest a thickness of 18-20 mils to properly cure. The thickness of the matchbook cover is approximately 18 mils. If you’re not sure how thick it is, pick up a mil gauge. This is a simple, easy way to see the thickness of your gelcoat.
Spraying Gelcoat: Please follow the instructions located on the products page or the label. Spraying Gelcoat delivery rate of no more than 2.5 pounds per minute with conventional air atomized spray, and no more than 4 pounds per minute with airless equipment. Spray: Airless or Conventional: 2.0-2.5 orifice tip. Use a gelcoat spray gun such as ES Manufacturing Gelcoat Spray Gun G830, ES-G100 Spray Gun , or equivalent.
You will need to thin the gelcoat for it to run through the spray gun. There are 3 major thinners that can be used when spraying gelcoat: Styrene, Patch Booster, and Duratec. The most cost effective and basic option is Styrene. Generally, you should not add more than 10% Styrene by volume. Patch booster is used with a 5:1 ratio or about 20% by volume. Do not use any other wax additive when using Patch Booster. Duratec is for a cosmetic high gloss finish. It has to be mixed at a 1:1 ratio with gelcoat.
Initially spray a cover coat as smooth and evenly as you can to cover your repair. This coat should be mostly in the repair area, and may be repeated. Sanding between coats is not necessary unless a surfacing agent has been added to your gel coat. Once your repair is covered, feather a ‘flow’ or sanding coat on the masked-off area making layered passes to avoid a buildup of gel coat in any one area. Each of these coats of gelcoat may involve several passes. Be even and consistent in your gun movement, overlapping each previous pass slightly and not hesitating on the ends. When spraying to a radius, flow the gelcoat to the tape. In open flat areas, layer passes. Final thickness should be 16-20 mils minimum or the gelcoat may not fully cure. Gelcoat needs to be applied evenly. We suggest a thickness of 18-20 mils to properly cure. The thickness of the matchbook cover is approximately 18 mils. If you’re not sure how thick it is, pick up a mil gauge. This is a simple, easy way to see the thickness of your gelcoat. As soon as you are done spraying, clean your sprayer fully with acetone. Most re-sprayed gel coat will cure in 2-4 hours, although overnight cures are ideal.
Finishing your Gelcoat Application: If you’re using our Professional Grade Exterior Gelcoat, you’ll be ready to sand and buff your freshly gelcoated surface after about 1- 3 hours. If you’re using our Brushable Gel Coat, you’ll want to let it cure overnight to make sure it’s completely cured. Begin wet sanding with the finest grit that will remove orange peel in the re-sprayed area. This will avoid unnecessary sanding scratches. Usually 320 or 400 grit wet paper is sufficient for the initial sanding. Going up to 400, then 600, and eventually 800 grit sandpaper. Compound and polish with Aquabuff 2000 then happy a wax such as Collinite 925 UV for protection.
Another option is you can use an 800 grit compound for the gelcoat at this stage. You want to use a buffer that turns 1600-3000 RPM. The car polishers won’t work if they’re spinning too slowly, so you want to check the speed of the spin. It’s best to do a 4 foot by 4 foot area at a time. Every 10 feet or so, you’re going to want to clean your pad with a spur or some air to make sure the contaminants don’t scratch your surface. If you want a perfect, glossy shine, use a machine glaze and then two wax coats, and you’ll have a stunning, glossy professional finish.
IMPORTANT GELCOAT APPLICATION TIPS:
DO NOT WORK IN DIRECT SUNLIGHT -Choose a shady location or an overcast day. You should catalyze your material so that it cures as quickly as possible within your working time. Generally mix one-pint batches. A good practice is to pour the mixed gel coat from the mixing container into another container used for application. This further assures that no uncatalyzed material is clinging to the sides of the pot. “Lay on” the gel coat in a heavy thickness (about 10 mils) using horizontal strokes, and working from top to bottom. Avoid re-brushing as this could remove the waxy surface additive. Remember to always lap wet. Generally, one heavy coat is sufficient. However, if you have opacity problems two coats may be necessary with a light sanding between coats. Once the coating (gelcoat) has cured, it should be block sanded using a 250 wet grit paper to remove all brush marks and high spots. Following this, it should be wet sanded with 320, 400 and 600 wet grit paper, buffed, polished and waxed.
Clean repair area and all tools with acetone prior to application
Pot life (amount of time for application of the product) shortens dramatically as you mix larger batch sizes. Keep in mind that you have a limited time to apply what you have mixed (usually between 5-15 minutes).
Measure catalyst accurately. Under- or over-catalyzed gel coat will cure slower and look faded or chalky.
Use the recommend thinners / additives only which are listed on the gelcoat’s product page. (No Thinning Necessary for the Ultra Plus Brushable Gelcoat)
Gel coat will not fully cure without adding a surfacing agent or over spraying with PVA
Check color thoroughly before applying. Gelcoat will not darken or change colors when it dries. The color wet is the color when dry.
Store gel coat in a cool, dry place
Gelcoat should be applied in temperatures of 60ºF to 80ºF
Always use eye and hand protection
Gelcoat should not be applied over paint, wood, metal or concrete. It usually will not adhere to these surfaces.
Gelcoat will not fully cure without adding a surfacing agent or wax additive sanding aid. You can over-spray with PVA before gel coal reaches its gel stage (5-10 min.), or adding 1oz per quart/ 4 oz per gallon of wax additive sanding aid.
Read all warnings on product labels and only use additives recommended as described per each product.
In order to have a form from which to develop your mold, you must either build the article from scratch using wood, plaster, polyester putty, formica, sheet metal, etc. or you must have on hand a completed article which you wish to duplicate. The latter is of course the fastest method. The plug is generally a male model exactly like the item you wish to fabricate in every detail. If the plug does not have draft (taper) then you will have difficulty getting parts off. If the plug has reverse bends, like many canoes, then you will need to make a split mold which can be spread or taken apart.
If the plug contains soft materials on its surface such as plaster, wood, or putty, then it will have to be sealed with lacquer orresinto fill the pores. If plaster is used, it must be oven dried and then sealed.
To prevent your mold from sticking to the plug, the plug must be coated with plastic film known as “PVA.” This is a plastic dissolved in alcohol and has a green color. It can be brushed or sprayed on, but the best system is to spray on three thin coats, the first being a “mist coat.” The appearance will then be green. Each coat must dry half an hour or so and there must be no pools or drips to blemish your mold surface. For the easiest possible parting, before applying the PVA, apply a soft wax (TR Mold Release) formulated for use with PVA.After the third coat ofPVAhas dried, a coating of this wax can be gently applied over it for easy parting.
The first step is to apply a gelcoat which will be the mold surface. Thegelcoat must be “exterior gelcoat” (wax free). If many parts are to be taken off the mold, it is desirable to use a“tooling gelcoat” which is designed to give longer life in mold use. The gelcoat should be in contrasting color to the surface of the part you will make. Since most parts are light colored, black gelcoatis commonly used. This facilitates spraying up a uniform thickness of light colored gelcoat since the black will show through thin spots.
If the gelcoat is to be brushed on, two coats must be applied, and the first coat must cure several hours before the second coat is applied. The best means of gelcoat application is a simple gelcoat gundesigned for the purpose and easy to clean. Air pressure of 80 to 90 pounds is desirable. Gelcoat must be applied at least 15 mils thick, or a quart to every 25 square feet of surface. If the plug was rough so that considerable sanding of the gelcoat will be necessary, then double the application. Before applying the gelcoat, it must of course, be catalyzed with MEKp peroxide hardener, using from one to two percent. All gelcoats from the Bottom Paint Store include the MEKp.
When the gelcoat has cured so that it cannot be scratched off with the fingernail at the edge of the mold, which takes from 2 to 4 hours to overnight in cool or humid weather, you are ready for the “skin coat.” This is a layer of ¾ or 1oz. fiberglass mat, thin enough so you can see and remove all air bubbles entrapped by the resin when you “wet-out” the mat. The resinshould be applied with amohair roller or brush until no white fibers remain. Any air bubbles are then eliminated with a grooved plastic or metal laminating roller. The polyester resin used should be “lay-up resin,” which is wax-free. Be careful not to over-catalyze when laying up the glass. Above 75°F one 10-15 cc of hardener to the quart will generally suffice. Below 70°F, 20 cc per quart. Do not work below 65°F.
In laying up a fiberglass mold, warping can be avoided by allowing each layer to “kick” or gel before proceeding with the next layer. For a large mold, it is good to apply just one layer per day. After the “skin coat,” you can use 1½ oz. fiberglass mat for a faster build-up. Generally, woven roving is not used in molds because the pattern transfers through the mold to the gelcoat. If it is necessary to use woven roving fiberglass for strength in a large mold, it is applied after a thickness of 3 or 4 layers of mat has cured hard. The thickness required in a mold depends upon size and shape and the number of parts to be taken off. For a dinghy mold to be used only a few times, four layers of mat might be adequate.
Removing mold from the plug
Allow mold to cure several days if possible so it will hold its shape. The first step is to trim the excess laminate back to the molded edge. This is easily done with a saber saw and a metal-cutting blade. The edges are sanded carefully until the line between the mold and plug is exposed. Then a sharpened “tongue stick” is forced between mold and plug to separate the edges. The stick is then pulled clear around the plug until all edges are free and no bridges remain. Avoid using metal tools for this purpose as they will scratch the mold surface. Then the mold should pull free of the plug. If not, the parts can be flexed or pounded gently with a rubber mallet. If necessary, air or water can be forced under pressure between plug and mold. A hole can be drilled through the interface for this purpose. PVA is water soluble, which facilitates parting with water pressure.
Polishing the mold
Depending upon the condition of the mold surface, it may have to be sanded with 220 grit working up to 600 grit wet or dry. The surface is then compounded with regular and fine finish compound formulated for fiberglass work. Best results can be achieved by using special compounds such as 3M Finesse-It Marine Paste Compound to bring out a mirror finish.
Before using a mold, it should be allowed to cure a week or more if possible. Be sure to use PVA parting film and soft wax for the first 3 or 4 parts, after which a carnauba wax can be used.
Alligatoring, or wrinkling, can result from:
1. Gelcoat too thin in some spots
2. Insufficient hardener, or hardener not mixed will enough.
3. Gelcoat not cured long enough before mat lay-up.
4. Acetone cleaner drips out of roller or brush during mat lay-up.
Original technical article provided by Fiberglass Coatings.
As you haul your boat out of storage you may want to get the gelcoat shining once again. Use the steps below as needed:
Which Products To Use: If your boat is new and the finish is still in good condition with little to no oxidation, you can use a one-step clean-and-wax product that combines washing and waxing in one step. We recommend using the 3M Marine Cleaner and Wax.
If your boat has light gelcoat oxidation use the least aggressive method, if possible, to prolong the life of gelcoat. We recommend cleaning with marine boat soap and buffing with the 3M Imperial Compound. Avoid direct sunlight and room temperature is best for application.
Note: An easy way to determine if gelcoat is oxidized is by wiping your hand across the surface. If any chalk wipes off on your hand, the gelcoat is oxidized and you will need to wash and buff the surface before polishing.
Follow these three simple steps to polish your gelcoat:
Step 1: Once you know which polish to use we recommend using a high-quality microfiber towel to apply the product. Avoid low-quality towels because they will shed fibers and leave streaks and residue on the boat.
Step 2: Wet the microfiber rag, remove any excess and apply a tablespoon of polish to the rag. This amount of polish will work for a few square feet. Remember, you want to work in small areas in order to cover the entire surface correctly.
Before buffing, spread the polish evenly across the boat’s gelcoat. You will get the best results when working the polish into the surface with circular motions.
Step 3: Once the polish dries into a haze you can remove it with a clean dry rag. Make sure you get in all the nooks and cracks for a smooth beautiful finish.
If your boat has been in contact with the elements over long periods of time (10-15 years), the process of restoring the appearance of the gelcoat will take some additional steps.
Step 1: Clean the surface. For boats that need a more aggressive cleaning just wash the surface and remove any loose contaminants. You can use a non-abrasive light detergent (marine boat soap) to remove all surface dirt and all previously applied coatings. If you need something stronger to remove surface rust, oil, tar, algae discoloration, black streaks caused from water runoff, exhaust and waterline scum, or other stains we recommend using an acid-based stain remover like Hammerhead Hull Cleaner. It is important to completely remove all stains before waxing, or you’ll seal in the stain.
Step 2: Select your compound. If your boat is a bit more oxidized a rubbing compound (liquid abrasive which “sands” your hull) is needed, but do so carefully as you can run through the gelcoat. The more faded your hull the more compounding you’ll need. The 3M Imperial Compound usually applied with a polisher if possible and compatible 3M pads, like the white 100% wool pad, recommended by 3M. Keep product off bottom paint, if applicable, by taping off as it can spatter. If the compound isn’t strong enough for your level of oxidation and scratches, then you may need to “pretreat” with a 1200 (or 800) grit as needed prior to the compound.
Note: When buffing, you should work on small sections of the hull (3-5ft sections is recommended). It is important to keep the wool pad damp. If you notice the pad is dry and the wool looks ‘matted’ after working the material into one area, just rake the wool back into form with a pad spur and re-wet the pad to continue with the application.