The first step in boat gel coat repair is to inspect the surface. Look for cracks, dents, scratches, and blisters. A few minor nicks, scratches, and gouges may be repaired with marine paint, but most gelcoat damage requires a more labor-intensive Gelcoat repair process. These steps involve wet sanding, compounding, and polishing.
Even the most pristine fiberglass boat isn’t immune to nicks, scratches and gouges from normal wear and tear. Whether from the rope chafing on cockpit coamings or the occasional dropped champagne bottle, there is a certain amount of cosmetic damage expected from life on the water. But these gel coat blemishes don’t have to be permanent. With the right preparation and process, these unsightly marks can be eliminated and blended into the surrounding gelcoat for a completely seamless repair.
The first step to restoring the appearance of gelcoat is sanding the damaged area to remove any remaining sealant or paint. The sanding process should begin with 180-grit wet-or-dry sandpaper. When that starts to show signs of fading, switch to 320-grit wet-or-dry paper and then 400-grit wet-or-dry. When the sanding is complete, clean the area again with acetone.
Surface scratches can be buffed out with rubbing compound, but deep gouges must be filled in order to look natural. Fortunately, this is easier than most people think and can be done by using a gelcoat filler paste that provides both the filler and finish in one application.
When using a gelcoat paste, be sure to mask off the surrounding area of the hull with 2 inches of painter’s tape. This will prevent any inadvertent sanding or application of gelcoat to adjacent areas. This will also protect the fiberglass laminate from sanding dust and abrasion during this phase of the repair.
Once the area is smoothed out, a small amount of color-matched gelcoat must be applied to fill in the gouge. This is where it pays to have some experience with sanding and polishing as well as some sanding tools. If you’re unsure about this stage, call in a professional to avoid mistakes that could cost you money and time down the line.
This example shows the repair of a white gelcoat, but the same procedure can be used for pigmented gelcoats as well. Just be sure to use an epoxy resin and filler as opposed to a polyester because it will adhere better to the fiberglass and last longer.
The next stage in boat gel coat repair is to fill cracks that have become brittle. These can appear as single-line gelcoat cracks or a spider web of cracked lines. This is a natural part of the life cycle for gelcoat and can be a sign that your fiberglass boat structure is under stress. These cracks can be caused by a variety of factors including age, exposure to sunlight, water, sand and other chemicals.
These cracks can be repaired using the same technique as for scratches and gouges. Acetone is used to remove the thin layer of gelcoat that is over the damaged area. A good quality epoxy-based filler is then used to fill the crack. The epoxy-based filler should be tinted to match the color of the surrounding gelcoat.
After the filler has been sanded back with 240-grit paper on a sanding block, it is then machine-sanded with 400-grit to make it even and give it a super-smooth finish. It is then cleaned with acetone again to remove any wax or grease that may prevent a good bond between the repair and the rest of the gelcoat surface.
Once the repair is cured, it can be overcoated with a product like Durabak to provide extra strength and UV protection. This can be especially useful for boat owners who live in an area where the sun is particularly harsh.
If the cracks are on a load-bearing piece of equipment such as cleats or stanchions, they should be examined more closely. There may be a problem with the design of the equipment that needs to be addressed before attempting a gelcoat repair.
The threads on a screw can put pressure on the brittle gelcoat and cause it to crack. This can be avoided by countersinking holes so that the load is absorbed by the structural fiberglass rather than the brittle gelcoat. Cracks can also be caused by over-tightening of hardware or not using the right size pilot hole for screws.
If you own a boat for any length of time, it’s almost inevitable that some scratch or nick will appear in the gelcoat. Whether it’s from a muffed landing or dropping a pair of fishing pliers, these blemishes can be easily repaired by a DIYer, if the surface is smooth. Things get a bit more complicated if the gelcoat is textured or finished with a multitone color, in which case you’ll need to call in a pro.
If a scratch or nick is not deep enough to require structural fiberglass work, simply filling it with resin and epoxy-based filler will do the trick. The area is first cleaned with acetone to remove any wax or other contaminants that may interfere with the bond between the damaged area and the new gelcoat. Next, the area is sanded down with 400-grit paper. When you’re finished, the area is wiped down with acetone once again to remove any sanding dust or residue.
After the area has been sanded and cleaned, it’s ready to be primed. If you’re resurfacing the entire boat deck or hull, choose a primer such as Duratech vinyl ester or polyester that is designed for use with fiberglass, rather than auto primer. These products adhere to fiberglass much better than automotive primers.
You should also opt for a high-gloss marine paint rather than a low-gloss. Low-gloss products will tend to dull quickly and are more likely to chip or flake.
After the primer has dried (which takes about an hour), you can start refinishing your repair job. If you’re painting the whole hull, start by masking off any areas that aren’t being repaired. If you’re refinishing a small section of the deck, mask only the surrounding area so you don’t get epoxy or resin on any other parts of the vessel. Then, using a paintbrush and a rag, apply several thin coats of the marine gelcoat. Be sure to allow each coat to dry before applying the next. If you want your completed repairs to be as smooth as possible, give the sprayed gelcoat a few hours to cure before sanding and priming again.
The surface of your boat needs to be clean and dry before gel coat is applied. Any oxidation or contamination can cause the new coat to flake off. The best way to get the area ready is by lightly sanding the entire repair and then wiping it down with acetone. This is especially important if you are dealing with a textured or colored surface such as diamond non-skid. A few light passes with a fine sanding block should make the surface of your gelcoat repairs smooth and ready to receive a fresh coat.
Before you start applying gelcoat, take a minute to look at the area and consider what caused it. Most scratches and gouges are the result of impacts with hard objects such as winch handles or downrigger weights. They may be a sign that you need to shift the load or install stronger stanchions or cleats.
Deep cracks are another matter altogether. If they run across your bow or stern, it’s likely that there is some structural fiberglass damage requiring attention. You’ll need a different repair method than just gelcoat, which requires some expertise.
Once you’ve cleaned the surface, mask it off around the area of your gelcoat repair. If you’re working on a piece of the stem, this should include strips of cardboard to protect the stainless steel strap. Masking the stem can also help you to avoid sanding through to the metal below, which could create an expensive problem.
When the masking tape is in place, it’s time to apply some color-matched gelcoat paste. Mix it according to the manufacturer’s instructions, adding pigment if necessary to match the existing color. A thicker mix is recommended if you are using a spray application because it can limit dripping.
After the gelcoat has dried, you can remove the masking tape and wipe the repaired area again with acetone. A fine sanding with a sanding block and 400-grit paper should flatten it out, not forgetting to sand the edges of the repair. Next, switch to a finer 800-grit paper and machine-sand the repair. Again, be careful not to sand through the gelcoat to the base laminate.