Tag Archives: gelcoat

How to Identify the Type of Paint on My Boat

If you are looking at the topside area of a boat, and the surface has a gloss/shiny finish, the options are mainly Gelcoat or marine paint.

To tell these apart, you can use a couple of methods:

One method is to use rubbing alcohol on a white cloth and rub it over an inconspicuous area of the hull. If the surface starts to shine, then it’s likely that you have Gelcoat. Another option is to take a piece of sandpaper and gently rub it over an area where the finish appears smooth. If the paper doesn’t snag and pull up any fibers from the surface, then it’s most likely Gelcoat as well. 

If you are looking at the bottom of the boat, and the surface has a dull, flat sheen finish you most likely have some type of antifouling bottom paint. The two most popular bottom paints are self-polishing ablative and hard bottom paint.

The self-polishing ablative bottom paints work like a bar of soap, once the boat moves in the water or there is a current and or tide, the outer layer slowly wears away. It is easy to tell when a boat is painted with ablative bottom paint, simply rub it with a dry rag in an inconspicuous area of the hull. If the paint easily rubs off, you most likely have a self-polishing ablative bottom paint.

Note: compatibility within bottom paints can be tricky, we recommend checking the compatibility chart of the new bottom paint you are interested in applying, to ensure you prepare the surface correctly.

Here are the bottom paint compatibility and cross-references charts by bottom paint manufacturer:

Related Articles:

How do I know if my boat has Gelcoat on it or paint?
How to Apply Bottom Paint Over Existing Bottom Paint

Filler Options for Gelcoats and Resins

There are many common fillers used with gelcoat and resin and here we’ll help you pick the one that is right for you.

When using putty, a good rule is not to go higher than 1/8″ thick without adding a layer of glass to prevent any issues. With the various fillers, for the right working consistency, you’ll want about 60-70% mix to resin ratio.

Milled Fibers: Finer than chopped glass, makes a harder putty that is strong and coarse.

Walnut Shells: Brown in color and preferred for wood putty or nonskid since it has large particles. Good Strength and darker pigment.

Phenolic Microballons

Microballoons or Microspheres: Phenolic spheres are generally plastic or glass and hollow, intact spheres that are lightweight. This is ideal for making fairing compounds. The Microballoons are a more expensive option for filler.

Fumed Silica: Also known as Cabosil FIller or Aerosil Filler. This is a hydrophilic fumed silica. Fumed Silica provides little change to weight, color, or physical properties after cure, used in resins and gelcoats to make them hang on vertical surfaces, (too much can cause porosity.)

Cotton Flock: Made from pieces of cotton and thickens to an off-white color. Great for bonding many substrates, especially wood. The mixture also creates a multipurpose adhesive for many other substrates in addition to providing excellent substrate wetting and penetrating characteristics. Increases impact and abrasion resistance.

Chopped Glass Fibers

Chopped Glass: These are the biggest pieces of fillers and are most popular for use with resin putty. Perfect for corners, crack resistant, and doesn’t affect pigmented gelcoat. 1/4″ glass fibers make the strongest glass reinforced putty.

Gelcoat Putty – Repair Spider Cracks And Fill Gouges!

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.

For filling gauges and cracks, some tips:

This product uses MEKP, just like gelcoat so your working time is 8-18 minutes, depending on temperature. If catalyzed at 1% and it is in perfect conditions (77 F) you have a longer work time. To extend work time cool product down before use.

If filling holes, fill a little high to allow for shrinkage. Once it dries you can easily smooth it out with sandpaper. Recommended thickness at 1/4″.

Tip: You can apply gelcoat to match the color of your boat over the repair, or you can use our pigments to tint the gelcoat putty and complete the repair all at once!

Thinning Gelcoat and Using PVA

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 polyvinyl alcohol (PVA) before gelcoat reaches its gel stage (5-10 min.), or add 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 spraying 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.

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. Follow manufacturers instructions as added Mekp may be needed.

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. Follow the manufacturer’s technical data sheet as an extra hardener may be needed. Some customers use Styrene for thinning but the manufacturer warns it can affect the gelcoat colors although this is the most cost-effective option and doesn’t have the added wax.

How to Gelcoat your Fiberglass Pool Steps

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.

See the article How to Apply Gelcoat’ for more details on how to use gelcoat.