While we have our fair share of soft, kayak-friendly, sandy beaches, between these oases lie miles of less hospitable coastline. Granite boulders and bluffs, barnacle encrusted rocks and cobble beaches all seem to have quite an appetite for that thin, shiny surface on our boats known as ‘gelcoat’.
Fortunately, gelcoat repair is not rocket science. Anyone with the right materials and a bit of patience can make a munched section of hull look like new again. If done with care, the repair will be invisible, often only given away by the fact that it looks better than the rest of the hull!
• Finish Gelcoat: This is a type of gelcoat made specifically for exterior repairs, which cures properly without any special steps. The other, more common type of gelcoat, ‘laminating gelcoat’, will not harden on the surface if exposed to air. In order to get it to cure properly, it must be sealed off from the atmosphere, typically by covering it with Mylar or by spraying it with PVA (polyvinyl alcohol), a liquid that forms a waxy coating as it dries. Since finish gelcoat is much easier to work with, it’s worth the trouble to find it. All gelcoat products come with a small tube of MEKP (methyl ethyl ketone peroxide) which is a catalyst that causes the gelcoat to cure. It’s often referred to as gelcoat ‘hardener’.
• Organic Vapor Respirator: This is a mask that uses activated carbon filters to remove harmful vapors. Gelcoat is noxious stuff with a strong styrene smell that’s unpleasant and unhealthy to breathe. An organic vapor respirator makes the process safer and much more pleasant.
• Safety Glasses: Always a good idea.
• Protective Gloves: Latex, nitrile or rubber gloves will keep the sticky goop off your hands.
• Sandpaper: You’ll definitely need wet/dry sandpaper in 220 and 400 grit. If you want a perfect finish, sanding with 600 or 800 and 1200 or 1500 grit is faster than trying to buff out a 400 grit finish and helps produce a higher polish in the end.
• Sanding Blocks: My preference is for a rubber autobody sanding block for coarser sanding and a chunk of Minicel foam as a block for the fine sanding. The foam block also works well on concave and convex surfaces.
• Polishing Materials: Automotive rubbing compound (the orange stuff) will be sufficient to get a basic gloss on the surface and may well be all you need. Using polishing compound (the light tan stuff) will result in a truly high gloss finish. A coat of automotive wax (paste or otherwise) will seal and protect the surface, and provide the ultimate shine.
• Sponge, rags, paper towels, etc.
STEP 1: ASSESS THE DAMAGE
Is the damage only to the gelcoat (cosmetic damage) or is there damage to the underlying fiberglass (structural damage)? If possible, check the fiberglass for whitish cracks on the inside. If you can’t see the glass, press a thumbnail into it. If the fiberglass is cracked or soft, it must be repaired first, as there’s little point in putting gelcoat over damaged fiberglass. If the fiberglass is intact, proceed to Step 2.
STEP 2: REMOVE THE DAMAGE
In order to produce a strong repair, all the damaged gelcoat must be removed and the surface must be smooth, with feathered edges. Use 80 grit sandpaper on a hard block for this job. The autobody sanding block can have sandpaper installed on both the flat and curved sides, which can be quite handy.
STEP 3: MASK THE AREA
Masking helps to prevent the gelcoat from getting onto other surfaces where you don’t want it. It doesn’t need to be elaborate.
STEP 4: MIX THE GELCOAT
The instructions will explain how many drops of catalyst to use for a given amount of gelcoat. For a small quantity, only 3-4 drops may be needed. Using more catalyst speeds the curing, which can be useful if you’re forced to do repairs in cool or cold conditions. Mix the two parts thoroughly. Initially, they may not seem to want to mix, but if you keep at it, they’ll mix completely.
If you need to tint the gelcoat to match a colored hull or deck, I suggest that you tint more resin than you need and hold some aside. That way, if you need to add more to the repair, you have perfectly matched resin that you can use, rather than trying to color match another batch. You can save extra resin for future repairs by putting it in an airtight container and storing it in the refrigerator.
STEP 5: APPLY THE GELCOAT
Gelcoat can be a bit runny if you try to glob it on all at once. Painting it on in layers seems to work best, adding just a bit with each pass. You want to build up the new gelcoat until it’s slightly above the original thickness. Although it’s not necessary to cover finish gelcoat in order to get it to cure, doing so can be helpful in keeping it in place on a surface. Allow the gelcoat to cure fully.
STEP 6: SAND IT DOWN
Starting with 220 grit wet/dry sandpaper, wet sand the new gelcoat to bring it down to the thickness of the original gelcoat and blend it into the hull contours. Take your time with this step and concentrate on sanding down the high spots. If you happen to uncover any trapped bubbles in the surface (a common problem if you cover the gelcoat), don’t despair. Just finish the sanding, add more gelcoat to the low spot, then sand again.
STEP 7: SAND AND BLEND
Switch to 400 grit sandpaper on a soft block and continue wet sanding and blending the repair into the original finish. At this point, the repair will become almost invisible. Continue with 600 or 800 grit, then 1200 or 1500 grit (if you have it). Once you’ve sanded this fine, the surface will start to appear slightly glossy.
STEP 8: POLISH THE SURFACE
Using rubbing compound on a rag or a buffer, polish the surface until it’s glossy. Switching to polishing compound will further enhance the shine. Apply a coat of wax and you’re done!