I have an old 10' styrofoam boat (maybe a Sea Snark). I want to fill gouges and cracks. What is good to use? I'm thinking something like a wood filler but that can withstand the water. I also want to lay fiberglass or similar product on the inside floor. What resin can I use that will not dissolve the foam? My grandfather did this but it has finally come loose after 40-50 yrs! I will paint over all the repairs.

There must be a user group on the web for Sea Snarks. They have been around for a long time.
Anyway, I would think epoxy resin, not polyester resin, should be used. And don't use wood filler. Wood filler is made for, well, wood. Why not use the same epoxy resin you will use with the glass, but mix in a bunch of low density filler like micro balloons? Big name resins, like West System, work very well but are pricey. Check at your local marine chandlery like West Marine, or online. I have had good luck with the epoxy resin from US Composites in Florida.

http://www.westsystem.com/ss/

http://www.uscomposites.net/default.asp

Dave

Yes, polyester resin must not be used as it "eats" styrofoam very quickly.

I'd take your query to www.boatdesign.net

Lots of experts on full size boats hang out there.

Cheers,

Earl

Agree with all of the above.

Just a comment - I did a test during summer regarding the filling of holes in foam - both white (expanded) and pink/blue/gray (extruded). Took some of same foam and dissolved in acetone. Was able to get a pretty sticky/gooey blob and smeared in with metal putty knife. Overfilled and took about a week to harden. Then 80 grit disk sander to smooth off. Left some small potholes but small enough to use thickened WEST epoxy and then sand again. The "goo" is harder than the foam - but it is much less expensive to fill this way than with a lot of epoxy - unless holes/gouges are small.

White foam dissolved quicker and seemed to work better. Extruded stuff took more time/acetone to melt. You will have to "play" with acetone volumes to get the right consistency if you want to try this. This method causes fumes so should be done outside with mask and safety shield/goggles.

WEST works very well - but as noted can be expensive depending on the size to be repaired. Use WEST for applying fiberglass on deck/inside cockpit - but remove old (loose) fiberglass first.

Originally Posted by Dick L.

Took some of same foam and dissolved in acetone.

Also known as homemade napalm.

Originally Posted by Fokker Ace

Also known as homemade napalm.

Or styrene filler. Sometimes called plastic putty, can be bought in tubes at the LHS. I imagine that a styrofoam boat, exposed to a flame, would go up just as well.

Just getting ready for my planned "Viking Funeral" - and let the rest of the family worry about paying the water pollution fines from the burning boat.

What about using the expanding foam insulation to fill in the big spots, then sand flush and glass over? Or even the light weight spackle that some guys use for filling before glassing?

Dave

PS: Or just cruise around the neighborhood and look in back yards for a replacement Snark.