Category Archives: Gelcoat

How to Select a Spray Gun Nozzle Tip Size

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.

  1. 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.)
  2. 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.
  3. 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 Spray Guns. The ES G830 gun will support a range of 0.8 – 2.0 mm. The ES G100 and G200 gelcoat 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
0.8 Parting Films – PVA – very fine mist
1.2 Clear Coats – super fine finishes
1.4 All Around Tip – clears, base coat, single stage paints
1.6 General Purpose – light to heavy viscosity materials
1.8 Primers – will apply primer quickly
2.2 -2.5 Gel Coats and Resins – for thick resins and not paints

 

 

Bibliography

http://boatpaintguide.com/gelcoat-spray-gun-the-right-tool-for-a-great-job/#.U_80dfldVWg

http://esmfg.com/aspnet_client/g860_hvlp_gelcoat_spray_gun.html

http://www.finishsystems.com/qanda.html

http://www.international-marine.com/paintguides/mpg_paintapplication.pdf

http://magnum.graco.com/products/M_Pages.nsf/Webpages/0Spray_Tip_Info

http://www.carcraft.com/howto/ccrp_0511_paint_spray_gun/#ixzz3Bheyr89Z

 

Clear Coat My Bass Boat

how to apply gelcoatTypically 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.

Ironside Urethane

Ironside Urethane

The paints available in clear for spray application are the Supermarine Mono Epoxy, Two Part Epoxy, and Ironside Urethane. Paints typically cover 200-400 sq feet per gallon.

So paint vs. gelcoat, the thicker the coating the longer it takes for the sun to burn through. Time in the sun/elements is what will determine how long the clear coat lasts.

Use each product link for more information on price, application and  coverage (tabs under picture for specs/how to use).

How to Apply Gelcoat 

Topside Boat Paint Options: What are your choices?

 

 

 

How to Apply Non-Skid Paints

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.

  • Industrial Buildings
  • Amusement Parks
  • Utility Vehicles
  • Ramps
  • Mechanic Shop
  • Walk-in Freezers
  • Ski Areas
  • Handicap Utilities
  • Residential Decks
  • Stairs
  • Restaurant kitchens
  • Stadiums
  • Restrooms
  • Warehouse floors
  • Wooden Decks
  • Food prep areas
  • Hospitals
  • Schools

Floor GripWhen it comes to non skid paints, there are two types of paint you can go with.  The first category are non-skid paints that come with the non skid formula pre mixed. An example of this is the Supermarine non-skid paint  called Floor Grip, or Floor Grip II for wood. The supermarine paint is an easy paint to apply, especially for the “do it yourselfer”. For best results you will want to remove any of the existing paint on the surface with sand paper followed by a good pressure washing. This removes any grit or oil that may interfere with the adhesion of coats of non-skid paint you will be applying.

After cleaning the surface, you will need to let it dry before applying any primer. The recommended primer for this job would be SM-664D etching primer by Supermarine. Note, the Floor Grip II when applied to wood needs no primer. This will give a good surface for your non-skid paint to grip on to.

Please note: You only need the etching primer for Glazed tile, fiberglass, aluminum and composite materials. Once the primer dries you are ready to mix your non-skid paint. You may start by scraping the containe, using a stir stick, down the sides to help loosen the aggregate.  This step may be difficult and the use of a high speed mixer will ease the process as well as some of the SM-605 thinner . Once mixed for a good two minutes you are ready to apply the paint. Floor Grip Non-Skid Paint may be brushed or rolled on to a wet film thickness of 25-30 mils. The first coat is able to be recoated in 12-48 hours depending on the temperature and humidity levels. Try to avoid heavy overlaps on your strokes and heavy build up in single areas.

This non-skid coating comes in over 90 colors to choose from. Keep in mind the supermarine non-skid paint maintains its color and gloss without chalking, yellowing or fading.

The next option is to add non-skid to paint or gelcoat. This process is when you take paint/gelcoat and add a non-skid additive such as Duralux non-skid additive , Seahawk non-skid additive for gelcoat, Griptex for Awlgrip and Pro Tex for Supermarine paints

The additive for gelcoat is extremely easy and adds just one extra step to the gelcoat application 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, first punch holes in the lid 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. The same goes for the Duralux non-skid additive when you add it to the paint.

How to Repair a Gelcoat Scratch or Hole

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 compound as 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 paste or you can make one using gelcoat and 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 a gelcoat repair kit (see instructions here) or 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 need 3M’s Preminum Marine Filler or 3M Marine High Strength Repair Filler. These are for bonding and filling repairs above or below the waterline and can be sanded. Some customers perfer to mix some thickener (cabosil) and gelcoat to a thick consistancy. 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.

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.

For puncture holes through the gelcoat or several holes have been drilled through and need filling you can also consider using the Hawk Epoxy System. See information on how to choose the Hawk Epoxy kit.

Removing Stains from Gelcoat

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.

Clean and inspect the surface with a wash with a mild cleaner like 3M’s boat soap or some alternative stronger cleaners if needed. After cleaning, dry and inspect surface for needs to be addressed: scratches, dings, cracking and crazing and to fix these flaws before rubbing out the gelcoat and restoring its shine. See the fiberglass/gelcoat repair section for options and the West System Video for “how to” instruction.

Apply a fiberglass stain remover, like 3M Fiberglass Restorer and Wax , Mothers Marine Black Streak Remover, or 3M Marine Cleaner and Wax to 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 WaxScotchgard Marine Wax, or Mothers Marine Synthetic Wax to help keep that shine.

For more gelcoat restoration tips see our how to Maintain and Restore Gelcoat link.

How to Use Metal Flake in Gel Coat

Gel coat is a resin that is pigmented with color. The consistency of gel coat is very thick and is best applied with a spray 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 gelcoat 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 gelcoat. Mix the gelcoat inside a pail thoroughly with a paint stirrer to disperse the metal flakes. Stir the gel coat 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 gun to 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.

Related Articles: How to Apply Gel Coat

Gel Coat Color Match Chart

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.

Other Product Links:

How do I know if my boat has gelcoat on it or paint?

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).

Here are the products that you would need.

3M Premium Marine Filler

Gelcoat or Gelcoat repair Kit.

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.

 

How to Apply Gelcoat

how to apply gelcoat
Below you will find a detailed gel coat preparation guide on how to apply gelcoat to your boat RV or other surface. 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.

Prepping the Boat

    • 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.

Sanding Existing Gel Coat
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 gelcoat repair with 220/330. At this point, the repair is ready to prep and spray/brush with gel coat. When sanding flat areas use a rubber block. Use 3M Abrasives for best results.

Gel Coat Surfacing Agents

Sea Hawk 8140 Wax Additive: Add up to 4oz of 8140 Wax Additive per gallon for tack free surface on the final coat, or if applying one coat a recommended film thickness.

Sea Hawk Patch Aid 8185: Add 25-33% Sea Hawk Patch Aid 8185 when applying gelcoat for small repairs, to improve the working properties of traditional gel coat spray patches. Patch Aid is an additive that significantly improves the application, appearance and longevity of Sea Hawk Gel Coat patches, and also gives a faster cure, harder patch, superior gloss, consistent cold weather performance, superior color match, and less halo. Patch Booster also eliminates the need to thin, or add wax to gel coats prior to patching. Do NOT combine with Sea Hawk 8140. Use either one (8140,8145) but NOT both!

Additives

Tinting: Sea Hawk Neutral Gelcoat may be tinted using Sea Hawk colorants designed for use in Sea Hawk resins and gel coats. Do not use more than 1 oz tint per quart.

Thinning Sea Hawk Premium Gel Coat

Sea Hawk Premium Gel Coat may be thinned up to 10% with Sea Hawk 7125 Gel Coat Thinner, or 25-33% Sea Hawk Patch Aid 8185. Use one or the other. Do Not combine. Acetone is NOT recommended except in clean up. Always add thinner, tint, or other approved additives prior to catalyzing with MEKp (also known as the hardener). Over thinning will result in an inadequate thickness for full curing. It is always best to start with 5% and work your way up to 10% if necessary.

Catalyzing Sea Hawk Gelcoat with MEKP: 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.

MEKP Catalyst Levels

Spraying Gelcoat
gelcoat spray gunSea Hawk Gelcoat may be thinned for use in a gel coat spray gun or preval sprayer with MEK gel coat Thinner. Acetone is NOT recommended except in clean up. Do not use more than 10% by volume of thinner, and always add thinner, tint, or metal flake first then add the Catalyst or Hardener and mix thoroughly. Over thinning will result in an inadequate thickness for full curing.
Please note:

  • Sea Hawk 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
  • Sea Hawk Gelcoat will not fully cure without adding a surfacing agent or wax additive sanding aid. You can over-spraying with PVA before gel coal reaches its gel stage (5-10 min.), or adding 1oz per quart of wax addtiive sanding aid.
  • All Gelcoats from the Bottom Paint Store come with the MEKP catalyst and wax additive sanding aid, but additional amounts can be purchased.
  • Gelcoat should not be applied over paint, wood, metal or concrete. It usually will not adhere to these surfaces.

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. 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. 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. Wet sand to a 600 finish and buff with 3M Finesse-It Marine Compound and polish with Scotchgard Marine Liquid Wax.

Brushing Gelcoat – (Use a Brushable Gelcoat)

When applying gelcoat by brush, we recommend the Ultra Plus Brushable Gelcoat.  (Sea Hawk Premium Gelcoat is 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 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.

Finishing Gelcoat
The major disadvantage of most polyester coatings is that they cannot be applied in a perfect “self leveling” coat.  ( except the Brushable Gelcoat) Sea Hawk Premium Gel Coat must be mechanically finished by wet/dry sanding and polishing if a factory mold finish is to be expected. For best results we recommend spraying the Sea Hawk Gelcoat. Sand the entire surface to be coated with 150 grit sandpaper. If cracks or gouges are present, they should be repaired first. When sanding gelcoat is completed, the surface should be free of flaws and perfectly smooth.

 

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.

Important Tips

1. Clean repair area and all tools with acetone prior to application

2. 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).

3. Measure catalyst accurately. Under- or over-catalyzed gel coat will cure slower and look faded or chalky.

4. Do not add more than 10% by volume of MEK gel coat Thinner. ( Not necessary for the Ultra Plus Brushable Gelcoat)

5. Gel coat will not fully cure without adding a surfacing agent or over spraying with PVA

6. Do not work in direct sunlight

7. Check color thoroughly before applying. Gelcoat will not darken or change colors when it dries. The color wet is the color when dry.

8. Store gel coat in a cool, dry place

9. Gel coat should be applied in temperatures of 60ºF to 80ºF

10. Always use eye and hand protection

11. Read all warnings on product labels

Gelcoat Repair Kit Instructions

Gelcoat Repair KitThere are two Evercoat gelcoat repair kits available: Large Gelcoat Repair Kit, which contains 4 oz. of polyester gelcoat paste with liquid hardener, coloring agents, cleaning solvents, mixing cup and stick and Mylar film for smoothing the repair surface. Small Gel Coat Repair Kit, which contains 1 oz. of polyester gelcoat paste and all the same components as the larger kit above, except for the cleaning solvent.

Gelcoat Repair Kit Instructions:

  1. Make sure damaged areas are clean and free of dirt, grease and wax, etc.
  2. Enough Gelcoat paste should be added to a plastic mixing cup to make all repairs. One of the six basic colors may match the gelcoat. If so, mix approximately 1 part pigment to 20 parts gel paste (in other words, fill the cup 1/4in and add approximately 1-2 inch bead of pigment from the tube). The pigments can be intermixed to achieve various shades. Please refer to the color match chart for mixing suggestions. NOTE: Exact color match will be difficult, but weathering will blend in slight color differences.
  3. After the color has been matched, take enough of the pigmented gel paste to fix a damaged area. Place it on a clean piece of cardboard and mix with several drops of liquid hardener. NOTE: adding liquid hardener will darken the color slightly! Four drops of hardener in 1 teaspoon of gelcoat paste will give approximately 15 minutes of working time before the material begins to gel. Mix the liquid hardener thoroughly into the gelcoat paste.
  4. Apply catalyzed gelcoat paste to the damaged area, working in into the area with a spatula or plastic spreader. Squeeze off the excess material.
  5. For greater smoothness and higher gloss, this repair should be covered with a piece of the enclosed clear plastic release film, and left to cure.
  6. After approximately one hour, remove the plastic film and clean the repaired area with the enclosed solvent and a clean cloth (applicable to 100668 large kit only )
  7. Deep damaged areas may require several applications.
  8. The repaired area should be sanded with 600 grit wet sandpaper. Then, the area should be buffed with a fine rubbing compound and waxed.

How to Make a Fiberglass Mold

Making a Fiberglass Mold

The Plug

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 or resin to 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 of PVA has dried, a coating of this wax can be gently applied over it for easy parting.

The Mold

The first step is to apply a gelcoat which will be the mold surface. The gelcoat must be “exterior gelcoat” (wax free). If many parts are to be taken off the mold, it is desirable to use a “tooling gelcoatwhich 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 gelcoat is

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 gun designed 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 resin should be applied with a mohair 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.

Gelcoat problems

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.

Maintaining and Restoring Your Gelcoat

Gelcoat Restoration Guide
Keep your gelcoat in good condition by using these 4 steps:

As you haul your boat out of storage you may want to get the gelcoat shining once again. Use the steps below as needed:

New Boats:

M09009A one step clean-and-wax products combine washing and waxing in one step, best used on new boats where the finish is in good condition with little or no oxidation, try 3M Marine Cleaner and Wax.

Light gel coat oxidation? Best to use the least aggressive method if possible to prolong the life of gelcoat  Clean with 3M Marine Boat Soap and buff with the 3M Imperial Compound. Avoid direct sunlight and room temperature is best. Use a tape, like 3M 471 available in different lengths.

Older Boats:

Step 1: Boats that need more aggressive cleaning just wash surface and remove loose contaminants: Use a non-abrasive light detergent to remove all surface dirt and all previously applied coatings,  3M Marine Boat Soap or Marine Clean are ideal.

Sometimes 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 before waxing or you’ll seal in the stain. Usually you will need an acid-based stain remover like Hammerhead Hull Cleaner or  Hull Cleaner, Extra Strong by Tip Top Teak (test in an inconspicuous area first) using gloves.

Step 2: 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 rub 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, is 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. 

M05928-2Step 3: 3M Finesse-It II, more aggressive, or the 3M Perfect-It Machine Polish, brightest finish, will help provide a nice finish to the gelcoat after compounding and bring it to a gloss. Apply with the yellow pad by 3M.

3M Clean and Shine can help remove any wax residue.

 

Step 4: The last step is a wax coat such as Scotchguard Marine Liquid Wax or 3M Ultra Performance wax.  These help seal  and protect all the work you’ve just completed.

m09033Maintaining Gloss: Revitalize your gelcoat gloss without going through all the work again by using  3M Marine Clean and Shine when you wash your boat and before it completely dries.