Advice on bonding to urethane foam

[BobMan]

I'm new to this site, but I'm looking for some advice from the august members of this forum. I've excavated, partially, the hull of a Boston Whaler. I've reinforced the bottom with fiberglass and epoxy. I'm definitely replacing the foam with the same stuff that was there; 2lb density urethane pour foam. My question is:

Foam over cured epoxy, with amine blush washed away, foam over wetted out epoxy (this option is fading, in my opinion) or finally, amine blush washed away over epoxy, and a layer of ISO laminating polyester resin applied and foam applied over the wetted out resin. I'm leaning toward option 1.

I was originally planning on applying the foam to the "wetted out" epoxy. I built a little test fixture with a number of 1" square "test blocks" I applied epoxy to all of them and allowed two to fully cure and two remained "wetted out". I then poured urethane foam on them and allowed the whole thing to cure. The result? not really much different. When the blocks were pulled away from the foam, the foam broke below the bond as opposed to breaking cleanly from the test blocks.

I'm pretty much convinced that the urethane foam is tenacious enough to adhere adequately to the fully cured epoxy, but I'm wondering if there is any chemistry between urethane foam and a "wetted out" option I'm not aware of.

[apex1]

Option 1
There is enough adhesion between the PU and the epoxy.
Do´nt bring polyesther into the mix!

Regards
Richard

[rasorinc]

Epoxy eats some types of foam but not stryofoam. Be sure to check with the maker of the foam and get it in writing as if it is not compatable it will be an expensive mistake.

[apex1]

Stan, he wrote "urethane" foam! PU
Regards
Richard

[BobMan]

Thanks!

[lymanwhite]

you might want to use peel ply (100% nylon) on the epoxy coat. It will lift the blush / waxes, and give you a better (dimpled) surface to pour your foam on.
I looked into both Gouegon and Evercoat technical advice, and found that a urethane foam will adhere well to epoxy.

[Commuter Boats]

Originally Posted by BobMan

I'm new to this site, but I'm looking for some advice from the august members of this forum. I've excavated, partially, the hull of a Boston Whaler. I've reinforced the bottom with fiberglass and epoxy. I'm definitely replacing the foam with the same stuff that was there; 2lb density urethane pour foam. My question is:

Foam over cured epoxy, with amine blush washed away, foam over wetted out epoxy (this option is fading, in my opinion) or finally, amine blush washed away over epoxy, and a layer of ISO laminating polyester resin applied and foam applied over the wetted out resin. I'm leaning toward option 1.

I was originally planning on applying the foam to the "wetted out" epoxy. I built a little test fixture with a number of 1" square "test blocks" I applied epoxy to all of them and allowed two to fully cure and two remained "wetted out". I then poured urethane foam on them and allowed the whole thing to cure. The result? not really much different. When the blocks were pulled away from the foam, the foam broke below the bond as opposed to breaking cleanly from the test blocks.

I'm pretty much convinced that the urethane foam is tenacious enough to adhere adequately to the fully cured epoxy, but I'm wondering if there is any chemistry between urethane foam and a "wetted out" option I'm not aware of.

The job of foam in a Boston whaler is not to just fill in space but is a core. The original foam was closer to a 6 pound density and the probability of success is relatively low if very much 2 pound foam is utilized in a repair.
I know your question was about bonding and not foam quality but if you're interested in discussion that will improve the longevity of your repair, I'm open to continue this conversation.
Gerald