fiberglass prep


New Member
I have read somewhere that I should coat the hull with epoxy and let dry before putting the fiberglass on. Does anyone have any remarks on this method?
Prime 1st coat vs 1st coat with fiberglass cloth

Either way gives good results--if everything goes well. That caveat leads me to recommend a prime coat of rolled-on epoxy on the hull prior to fiberglass cloth if this is your first experience with epoxy. Murphy's law applies to your first epoxy job. The alternate way--incorporating cloth and epoxy together in your first coat--saves a little time but magnifies error opportunities.

Marine epoxy will soak into a sanded cedar hull maybe up to 1/32". The hull will continue to soak up epoxy until its saturated. You'll know after rolling on a prime coat of epoxy if the hull has absorbed as much epoxy as it's going to, as the surface will remain shiny. If you have rolled on an insufficient amount of epoxy to fully saturate in certain areas, those areas will be "starved" and will have a characteristic dull or dry appearance. You can then easily roll on a little more epoxy to those areas.

On the other hand, if you forego the prime coat and lay your cloth onto a newly sanded hull, then apply epoxy to the cloth, it's not as easy to see starved areas through the cloth/epoxy mixture. You run the risk of leaving starved areas which will still appear white in the finished hull after all the epoxy coats are on.

It's crushing to see ugly white areas on your first boat that you've probably spent upwards of 100 hours on so far. This is the voice of hard experience talking here.

So to be safe, I usually prime a cedar hull first, then put the cloth on when the prime coat is no longer tacky. If you are doing the fiberglassing in one marathon day, you can speed up the prime coat hardening by placing an electric space heater beneath the hull a few hours prior to rolling on the prime coat and for a few hours after the prime coat has been rolled on. Epoxy sets with heat, so have lots of it to set the prime coat as quickly as possible.

If you live in the Midwest and have access to a Menards Home Improvement Store they carry some wonderful little 6" foam rollers and 6" roller handles that are ideal for rolling on epoxy. They're a closed cell foam, so it really lays a neat coat of epoxy down. You'll still need to "tip off" the rolled coat lightly with a foam varnish brush to break up the bubbles that are left after the roller, but the whole prime coat--rolling and tipping--should take no more that 30-40 minutes. It's also immensely satisfying as the hull gleams afterward. After the prime coat is on and tipped, break open a beer and celebrate that striking hull!

If you're using an epoxy which has an amine blush upon setting, get the cloth on as quickly as the partially set epoxy prime coat allows. If you wait more that 6-8 hours after priming, you'll need to wash off the waxy amine blush before laying the cloth. If using MAS or one other non-blushing epoxies, you can prime the night before and spread the cloth first thing in the morning.