While gel coat is strong and durable, it is subject to damage just like any other finish. There are several reasons why it would need to be repaired. For this article, we are going to focus on cosmetic scratches and cracks. Not deep cracks below the gel coat that damage the fiberglass laminate.
We will give some basic guidelines on how to do the repair work. You do not need to be an expert to make a gel coat repair but it may take a little bit of trial and error to really perfect the art. It is more of an art than a science.
It is recommended that you take safety precautions when working with gel coat. This includes working in a well ventilated area and wearing safety goggles, a respirator and gloves.
It is important to work in temperatures between 70 and 85 degrees Fahrenheit. That is the ideal temperature to work with resin.
If the scratches are shallow, they can usually be wet sanded and buffed out. Deeper scratches and cracks are a little trickier to fix. We will focus on repair techniques for the deeper cracks on this page. The first thing you need to do is figure out why there is a crack or scratch in the gel coat. If it is from an impact, you should be able to fix it and not have it appear again. If there are underlying problems, the crack could come back.
Look at the repair area and mask it off with tape. This will protect the area beyond the repair site from getting damaged.
Next, clean the area you will be repairing by wiping off contaminants with a solvent such as Acetone. Sand it with a medium grit sandpaper (around 320 grit) to further get rid of contaminates. Using a sanding block helps prevent pressing too hard in some areas and not others. It will give you a nice, even sand.
Use a screwdriver or a dremel to widen the crack area into a “V” with beveled edges. Resin will not penetrate a small crack so it is important to make the crack bigger without grinding into the composite layer. Make sure the “V” is smooth and has no sharp edges. That way, the resin will adhere better to the repair site. You can sand again with a 320 grit sandpaper to smooth out any rough spots. Wipe clean with Acetone or other solvent.
Color matching the gel coat for the repair site can be difficult. You can buy a white or neutral based gel coat and add pigments to match your existing color. Or, you can send us a piece of the old gel coat (about a quarter size) and we will color match it for you. We carry a vast amount of colors that you can pick from as well.
The filler, Cab-o-sil, can be used to make a paste. Mix it in with your gel coat until it is a peanut butter consistency. Make sure to add the filler before the catalyst, MEKP, is put in. (MEKP is added between 1% and 2%). Work in small batches and make sure you mix well with a stir stick. Fill the crack from one end to the other. This helps to avoid trapping air bubbles. You will want to overfill the crack since polyester based resins will shrink. Make sure to pop any air bubbles that you see.
Gel coat without wax will cure with a tack (be sticky to the touch). You can carefully cover the repair area with plastic film, such as saran wrap, to prevent this tack. You can also add PVA, also known as poly vinyl alcohol, after the gel coat starts to cure. PVA is a film that will wash off with water. Another option is to add wax to the final coat of gel coat. The wax will rise to the top to create an air tight barrier.
Dry sand very carefully with a 100 grit sand paper and work up to 220 grit. Do this until the repair area is smooth and flush with the surrounding area. You can remove the masking tape at this point or you can wait until you are ready to wax. Work up to higher grits (400, 600, 800, 1000 etc) and add water for a wet sand. Buff the area with a rubbing compound and buffing wheel. You will finish up by waxing and polishing the entire area.
If you have any questions, go to our website at www.fiberglassandresin.com.