How to Do Gel Coat Repair on Your Boat
Gel Coat repair may seem intimidating, but it’s not a big deal with the right tools and materials. Keeping the fiberglass structure in good condition will prevent water damage and corrosion of metal components on your boat. Before applying the gelcoat, match the color by wet-sanding an area of the hull that is identical in tone. Protect yourself from noxious fumes by using a respirator and disposable gloves.
Repairing Deep Gouges or Chips
You can fix light scratches in gelcoat with rubbing compound, but deep gouges and chips require more work. To fix these you need to use a more permanent filler, like resin and an epoxy-based gelcoat filler or paste. These are available at marine supply shops, home improvement centers or paint supply stores. Look for a kit that includes a color match for your boat’s exterior gelcoat. You will also need a container of acetone to clean up any sanding dust or spilled gelcoat that could stain the surface. A small, hand-held vacuum or a hose attachment to suck up the acetone dust can be handy. Before you begin, tape off any sensitive areas or adjacent surfaces that might be damaged by gelcoat spatter or accidental sanding. A section of kitchen “zipper” bag works well for this purpose.
If the area around the chip is in good condition, you can proceed with a simple fill and sand with 180-grit paper. Then clean the area with acetone to remove any waxes or other contaminants that interfere with the bond between the damaged surface and the gelcoat.
Once you have the gelcoat filler or paste mixed to the correct ratio-follow the instructions that came with your product-use a putty knife to spread it into the gouge or scratch. Use a larger amount for deeper dents and smaller amounts for shallower dents.
This step is important for ensuring that the new gelcoat will adhere to the existing gelcoat. If the area is too sloppy, the new gelcoat will not stick properly and may peel or crack.
Then sand the area again with 120, 320 and then 800 grit paper to smooth it. Make sure you sand from both sides of the gelcoat to ensure that it is evenly sanded.
Now you can buff the repaired area with a rubbing compound to bring out a high gloss and a perfect finish. If the repair is done well, it should be virtually undetectable. If the finish is dull, wash the entire boat with a degreaser and then apply a second coat of rubbing compound to brighten it up.
A damaged gelcoat needs to be sanded down and cleaned before a new coat can be applied. A small amount of rubbing compound will remove the coarser scratches, and a good quality sandpaper, such as 80-grit, can be used to smooth the repaired surface and create a bevel for better adhesion. Once the sanding is completed, the repair area should be wiped down with acetone to remove any waxes or other contaminants that might interfere with the bond between the gelcoat and fiberglass.
A gouge is a deep cut in the gelcoat that exposes the fiberglass, and requires more extensive repairs than a scratch. You can assess a gouge by running your fingernail across the affected area. If the area doesn’t catch on your fingernail, it is a shallow scratch and can be repaired using gelcoat filler. Deep gouges that penetrate the fiberglass will require more extensive repairs, requiring fiberglass repair and a refinishing process.
Scratches are shallow cuts that don’t damage the fiberglass and can be repaired with gelcoat filler. You can assess a scratch by running your fingernail over the affected area. If the scratch doesn’t catch on your fingernail, you can use a filler to repair it, but more extensive damage may need a more extensive refinishing with fiberglass.
Masking the area surrounding the damaged area is recommended, particularly when using a spray-on application of gelcoat. This protects the undamaged areas from splatter and helps you stay within the boundaries of your work. If you are unsure whether you need to mask the entire area, try spraying a thin layer of gelcoat on a nearby piece of clear Mylar film (available from office supply stores). Once it cures, the Mylar can be removed and any stray spots of gelcoat can be touched up.
The next step is to mix the base and catalyst together for the gelcoat you are using, following the instructions on the label. The ratio of base to catalyst determines how long the gelcoat will take to cure, so it is important that the right ratio is used.
Wet-Sanding the Repair
Before you apply gelcoat, it is a good idea to wet-sand the repair area. This will help to make the surface even and improve the bond between gelcoat and hull. Use 320-grit wet/dry paper on a soft sanding block. Confine your work to the immediate area and keep it moving to avoid over-sanding one spot. When you are finished, clean the area with acetone.
The sanding may reveal some areas that need to be filled. If you see this, it is a good idea to call in a pro before proceeding. This will prevent structural fiberglass damage and may require a filler that is different than the gelcoat product you are using.
A few scuffs and scratches might be buffed away with rubbing compound and a coat of wax, but deep gouges or large areas of oxidation will need to be repaired. The gelcoat is only a thin layer and it is especially thin in corners, curves and other areas where the boat is not regularly used (Practical Sailor covers restoring a heavily oxidized gelcoat: December 2012 and February 2011).
In many cases, it will be necessary to use epoxy resin and fillers rather than polyester products for these types of repairs. This will require additional steps and may take longer to cure.
If the crack in your gelcoat is a result of impact with load-bearing equipment such as cleats or stanchions, it might be a sign that there is an underlying problem with those structures and this is worth fixing before you proceed to repairing the gelcoat. Cracks around these structures should not be ignored and can lead to further structural damage if left unattended.
Once the surface has been wet-sanded, it is a good idea to wipe it down with a lint-free cloth dampened with acetone to remove any contaminants that could interfere with the new gelcoat. You should also check the sanded surface for air bubbles to be sure it is as smooth as possible. Once the surface is clean, mix up a batch of gelcoat according to the manufacturers instructions and apply it to the repair area.
It’s a great moment for the fabricator when he releases the part from the mold and sees a perfect gel coat surface. But remember, the gel coat is part of the final composite, not a separate coating. It needs to be bonded chemically and mechanically with the reinforcing and resins in the final product, or it will delaminate and chip.
Gelcoat chips and scrapes from normal boating use aren’t a big deal, but if you notice a pattern of them around load-bearing equipment like cleats or stanchion bases, take a closer look at the base of the equipment to see if there is an underlying problem that needs to be addressed. It may be as simple as shifting the load from undersized equipment to larger equipment.
Before you apply any gelcoat, wipe down the area with a lint-free cloth dampened with acetone to remove any surface contamination that could cause problems with the new gelcoat. Be sure to wipe thoroughly, turning the cloth frequently, and work swiftly as once a gelcoat is catalyzed it starts to harden quickly.