A fiberglass boat is a lovely thing to work on.
Any time you add something, you essentially reinforce the hull.
Watch out, though - the “glass” part of “fiberglass” is just what it says. You better watch out for minute, tiny slivers of glass EVERYWHERE. Gloves are essential.
To work with fiberglass, you’ll need the material* and something to affix it with. The “glue” of choice tends to be epoxy, specifically West System (there might be other stuff. I wouldn’t know. We use West System, a Gougeon Brothers invention, exclusively.) This two-part epoxy is great.
You need a resin and a hardener, and you have to be VERY careful with the ratios. I won’t go into details about which resin and which hardener (they depend on temperatures you’re dealing with and how long you want it to be workable). The method of application, though, is pretty similar regardless of which particular resin and hardener you’re using.
1) Clean the area you’re going to work on. In our case, we were affixing wood tabs to the hull. We cleaned the hull (and the wood, come to think of it) by sanding/lightly grinding (wear respiratory protection!!!), and then wiping down with MEK, a particularly toxic solvent that requires good ventilation, gloves, and skin protection, and that respiration protection.
2) Cut the fiberglass to the right lengths. For this project, we used fiberglass “tape”, which just means it’s about 4” wide, as opposed to cloth that’s a LOT wider. If you’re doing major fiberglass work, you might be cutting HUGE pieces of cloth.
3) Prep your epoxy. We’ve got a TON of really old resin and hardener in the garage, and went through a chemistry experiment last week trying out each resin with each hardener to determine what might be useless. Most, I am happy to report (have you priced the stuff? Yikes!) is definitely viable.
You want to mix in small containers, in the aforementioned correct ratios. You can buy specially calibrated pumps for the resin and hardener, or you can use a syringe. Don’t use the same syringe for both resin and hardener.
Epoxy works by firing off a chemical reaction between the 2 parts, and you can use it until it “kicks”, or gets rock solid. We like to mix small quantities so we can use it all up before it kicks off. Did I mention epoxy is expensive?
4) “Wet out” the area you are fiberglassing - this means paint the epoxy onto the hull. It’s way easier to apply the epoxy to the hull than to the fiberglass.
5) Press the glass onto the wetted surface (it’ll stick) and really press it down. We used the paintbrushes (cheap chip brushes) to do this work; if you’ve got a thicker layer of epoxy you can use a squeegee to really press the glass into the epoxy. You’re trying to avoid any air voids.
6) Add another layer of epoxy and really wet the glass down. Then press on another layer of glass. No, don’t wait for anything to kick off or get hard or dry. You are working to bond the layers of glass together. If you wait for it to kick off, you’ll have to start the whole process over again - and that process starts with grinding. Press/squeegee the glass so there are no voids. It gets tricky sometimes as the glass material is pretty movable - it likes to stretch and warp, and the edges shed fiberglass fibers like nobody’s business. All the while you’re wearing gloves and dealing with super sticky stuff that’s starting to get hot and harder to work . . .
Let it fully cure (we usually allow at least overnight, even if it feels like it’s kicked off before that) before you do whatever you want next. For us, it’ll be affixing sweet ash strips to the hull by fastening them to these fiberglass tabs. The epoxy has 2 weeks to kick off nice and hard!
Do this in SMALL sections and SMALL batches
If you’re filling in blisters, you’ll have cut raw fiberglass into pieces that are successively larger. Keep going with this paint/glass/press/paint/glass/press routine until you’ve filled in your blister and the last couple of pieces of fiberglass overlap onto prime hull material.
Clean up quickly, using a nasty solvent like MEK or acetone. Wear gloves!
If you’ve mixed the epoxy in a plastic tub, you can clean it out well with a paper towel and let it finish hardening - the leftover epoxy will kick off and leave a fairly easily removed skin.
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