How to Apply Gelcoat – The End-all Guide

Gelcoat PhotoProperly applying gelcoat is the key to a good finish. Many of our customers are hesitant to use it, thinking it’s too complicated or they think they can’t end up with a good finish. So, we are here to provide a step-by-step guide on how to properly apply gelcoat. As with all our products, if you have any questions, we are here to help!

First thing you want to do is look at the surface you want to apply gelcoat to. If the surface is already covered with gelcoat, or if the surface is a fiberglass, or polyester resin, then applying gelcoat will be a snap. If the surface is paint, then the paint would have to be removed before applying the gelcoat.

gelcoat-sandingSo, you’ve decided the surface is gelcoat, so it’s time to begin. You want to sand the surface to create a mechanical bond with the gelcoat. Start by sanding the surface with 150 grit or lower sandpaper. Our technicians recommend using Dyekum Steel Blue to be very thorough. Steel Blue is a dye you wipe on. Once you don’t see the blue dye anymore, you know you have properly sanded everything. You can also use a pencil, but it’s harder to see and won’t guarantee complete coverage.

Next, you want to clean the surface. We recommend using Acetone, as it doesn’t leave a residue and evaporates quickly. Once the surface is clean, you want to get going pretty quickly; if the surface sits for any extended amount of time, you will want to re-clean the surface. Dust and dirt particles are your enemy here, so be thorough on the cleaning.

We are ready to gelcoat! First, decide if you need one or two coats of gelcoat. It will take a minimum of two coats of gelcoat if you are changing colors. If this is going over a patch, we recommend 2 coats at least, to get a nice, uniform surface. Otherwise, one coat will do.

Gelcoat needs to be applied relatively thin. We recommend 18 mils mil-gauge-2thick, to properly cure. 18 mils is approximately the thickness of a matchbook cover. If you aren’t sure how thick, pick up a mil gauge. It’s a quick, easy way to see the thickness of your gelcoat.

Gelcoat requires Methyl Ethyl Ketone Peroxide or MEK-P to activate the hardening process. The amount is very small. We recommend 1-1/4% to 1-1/2% by volume, which means 13-15cc’s per quart. Darker colors require a bit more catalyst for the same reaction, so you can catalyze up to 2%. Refer to the catalyst chart on the side of the can, or you can find one HERE.

Be sure to have a plan of attack for applying your gelcoat. Once you mix it, you have about 15 minutes to apply the gelcoat before it starts to get hard or “gel.” The actual working time depends on your amount of catalyst and how hot your working conditions are. Anything below 60 degrees, and your gelcoat will not cure, but as you get warmer and warmer, your working time decreases rapidly. At 70 degrees, you get your 15 minutes, but at 90 degrees, you only have about 5 minutes. If you need more working time, be sure to sit the can in some cool water, or even some ice to cool it down to 60 degrees give you a bit more time.

Brushable gelFor applying your gelcoat, you can either roll the gelcoat on, like paint, or you can spray it on. We also sell a Brushable Gelcoat that can be applied with a brush. If you decide to roll on the gelcoat, be sure to use a solvent-resistant 1/8” or ¼” nap. Be sure not to use foam rollers, as they tend to leave bubbles. If you brush it on, be sure to use a solvent resistant brush. Your first coat will simply consist of the gelcoat and the MEK-P catalyst. Once applied, you want to wait about an hour and a half, for the gelcoat to set. It won’t be completely cured by then, but it should be hard and tacky.

Your second coat will consist of the same amount of Catalyst, but if you are doing one more coat, your next coat will include Sanding Aid, or ‘wax.’ You will mix in 1 oz per quart to the gelcoat, which will seal the surface from oxygen, causing the gelcoat to dry tack-free. If you roll or brush your seconding coating, be sure to go the opposite direction from the previous coat, allowing a uniform coating.

If you are using our standard Exterior gelcoat, you will be ready to sand and buff your freshly gelcoated surface. If you are using our brushable gelcoat, you will want to let it sit overnight to ensure it’s completely cured. To start sanding, begin with 320 grit sandpaper and sand the surface completely. From then on, start going up to 400, then 600, and finally 800 grit sandpaper.

At this point, you can use an 800 grit compound to compound the gelcoat. You want to use a buffer that turns at 1600-3000 RPM’s. The car polishers will not work, as they spin too slowly, so you want to check the spin speed. It’s best to do a 4’ by 4’ area and go from there. Every 10’ or so, you will want to clean your pad with a spur or with some air to ensure pieces don’t scratch your surface.

If you want a beautiful, glossy shine, use a machine glaze and then two coats of wax, and you will have a beautiful finish that any professional would be envious of.

Interior vs. Exterior Gelcoat

Brushable gelGelcoat is a big part of our business here at FGCI. When looking at gelcoat, there is a wealth of options to choose from. The most obvious first choice is the color of the gelcoat; we have a vast array of over 25 stock colors with the ability to color match to a sample you provide. Once you have the color figured out, comes whether you want to brush the gelcoat or spray it, as we have the ability to do either. Lastly, however, is the option many people have a question about; interior or exterior. Let’s look at both options so you know which you will want for your job.

Exterior Gelcoat is our tried and true standard. If our gelcoat doesn’t specify interior or exterior, then the answer is automatically exterior gelcoat. It doesn’t mean that the gelcoat is only good for external use, or the outside of a boat, it means, simply that it does NOT have wax or Sanding Aid mixed in. This means that the lack of Sanding Aid will result in a tacky finish. If you want to avoid the tacky finish, you will want to add something like Sanding Aid, Patch Booster or Duratec to the mixture. This is mainly used as your primary coat or coats as you do not have to sand between coats, given you don’t wait too long.

Interior Gelcoat doesn’t mean the gelcoat can only be applied inside, it means it has Sanding Aid or Wax mixed in. Interior Gelcoat is used as a final coat, due to the Sanding Aid allowing it to dry tack-free, it will give a nice finish. You will not want to add Duratec or Sanding Aid to this product. If you use this product as your primary coat and look to add another coat, you will need to sand it first.

Now that you know which product you need, you can buy your gelcoat with confidence. And as always, remember that we are here to help with any questions you have!

4 Tips for Using Brushable Gelcoat

Brushable Gelcoat Photo1. High quality paintbrushes and rollers will yield the smoothest surface upon application.
2. If you want to prolong your working time, you can chill the brushable gelcoat down to 60°F.
3. Spray guns that have a 2.0 nozzle or bigger can be used to spray brushable gelcoat.
4. Brushable gelcoats are intended for use under controlled industrial conditions and are not recommend to be used below 65°F.