Foaming epoxy

surfdad 06-02-2009, 8:45 PM

Arguably, the heaviest part of a board is the resin. It's heavy and there is a bunch between lamination, hotcoat and glosscoat.

I was hotcoating a board tonight, normally I mix up about 2 oz more than I'll need. Tonight I pushed the excess epoxy back into the bucket.

When you push epoxy around it foams, but typically subsides.

The epoxy I used tonight cured all foamed up. It displaced at least 20 times the volume as the residual I normally have.

I'm not sure what to do with this information, but if I couls use 1/20 the norm, I could cut back on weight significantly.

Normal 2 oz residual:

Upload

Foamed 2 oz residual:

Upload

(brewkettle) · (brewkettle) **Join Date: Jan 2009** 06-03-2009, 8:03 AM

some sort of contamination or something , you need to try greenroom epoxy. how many oz's do you use for a cheater coat and a hot coat on your boards you build??

surfdad 06-03-2009, 8:12 AM

This is a super cheap epoxy, but has an incredibly stiff modulous. No contamination - I just pushed the epoxy around a BUNCH and that will cause the foaming. What was funny was that it expanded as it cured.

I typically mix up 4 to 5 oz and then use 2 oz or so on the board...I like to have extra in case I screw up :-)

(bac) · (bac) **Join Date: Feb 2008** 06-03-2009, 5:25 PM

Jeff, quick question, and please excuse my ignorance on hotcoating. Would the strength of the epoxy be compromised? I understand it wouldn't be as strong as with a normal coat of epoxy, but how much weaker would it be, or is it hard to say? Since it expanded while curing, how difficult would it be to get it to smooth out? The expanded stuff looks pretty porous.

I'm sure I'm thinking way too much into this

surfdad 06-03-2009, 7:45 PM

Yeah - I have all those same "concerns", I'm not quite sure what to do with this discovery. I would think it be useful in only certain circumstances...maybe in laminating a sandwich layer, where "flex" is ok and the porous nature of the cure is ok.

I think I figured out what is happening. The air bubbles in the epoxy get trapped and then expand with the heat from the exotherm while the epoxy is still soft. Then it cures with the bubbles pretty large - at the base, some of the bubbles broke or combined to leave a large void.

Epoxy, by itself, is a medium soft plastic - sort of brittle and at the thickness found in a board, not very stiff. It's the addition of the fabric in the matrix that gives the strength and stiffness.

I want to do some experimentation joining some parts like gluing up rails or the skins.