Epoxy adhesion

I want to glass the bottom of the board [carbon/kevlar] & then be able to still shape the foam on the deck before glassing that.

My concern is about the bond on the rails & the possibility that it will delaminate under flex.

Is there a good way to do this?..& is there any way to soften the epoxy to create a chemical bond.

Thanks in advance for your help.

from my experience with composite vacum molding in aircraft structures,

when there is a complex part that needs to be molded in several stages ( e.g - # of layers in sandwitch construction)

I use peel ply between each stage.

the peel ply is supposed to absorb excesive resin and also sucks any contamination in the fabric and

also leaves a rough surface alowing a real good mechanical bond between each layer/stage of work.

this is the method used in the aircraft industry and you probably know how strict the rules are in that kind of

aerial structures .

hope it helps,


Thanks for that info Lee.

I presume you would just leave it on until the deck needed glassing. Would it be best left on until the epoxy is fully cured…or is there some chemical bond with a partial cure?

Would you use 100mm wide strips in this situation & is it a problem to get it to lay flat & also to see trapped air etc?

Uhmmm- if you’re looking for a chemical bond to the foam, I’d actually travel a different path. See, something that’d chemically combine/bond to the foam would also probably be a solvent for said foam, such that it’d dissolve it.

A good example would be what happens when you attempt to laminate on styrene foam with polyester resin which in turn often contains styrene monomer as a thinner/modifier. The foam basicly turns to a gassy semi-liquid.

The other consideration is that while you can get a good and strong bond, laminate to foam, the mechanical strength of the underlying foam - well, it ain’t much, you know? When you look at a busted board, you see a thin layer of resin-impregnated foam adhering to the underside of the laminate with maybe a little un-impregnated foam un the underside of that: surface foam breaks away from the rest of the blank.

So, back to it- a good mechanical bond ( maybe vaccum-bagged ) is about as good as you’re gonna get.

Now, from what you’re describing, it sounds like you’re working on a flex kneeboard? I’d think the best way to play it to avoid delamination would be to work with the cross sectional shape of your foam, as finish shaped. Like this:

Keep the height ‘r’ as low as possible and minimise sharp transitions while maintaining enough volume to achieve the required floatation so that, basicly, the thing doesn’t sink . The relatively ‘tall’ sections will also inhibit flex considerably.

I will note that some very good flex boards have been built that completely ignore this, but they used relatively high strength/high shear strength stuff that wasn’t surfboard foam and the boards were made with a very different procedure: vac bag the bottom onto a mold, remove from mold and cut to outline shape, vac bag sheet foam on and shape foam as required, vac bag the remaining laminations.

Hope that’s of some use


For the best possibe bond of glass to glass at the lap on the rails you should do each side a soon as possible and withing 24 hours but, epoxy can take up to 3 weeks to fully cure are normal temprature, so if you rough up the weave with 60 grit and then wipe down with DNA you should still get a good bond.

My question would be why would you wont to glass one side and then finish shapping the deck? the may be a more straight forward solution that would allow you to glass as normal.

Are you making a spoon by any chance? how long will it take you to skoop the deck out, I would bet you could be done with the shapping and glass the deck within 48 hours of doing the bottom.

Thanks for your input Doc & Woody & thanks for the work & thought you put into the post Doc.

I’m working on three boards at the moment…one kneeboard and also a 7’ 3" & 7’ 6".

My requirement is to be able to shape down onto a solid bottom when shaping the deck…they are not spoons…but might have some distant spoon DNA in there!

I’m only really concerned about the rail lap strength [glass to glass] rather than glass to foam, so I guess that maybe the best bet is to go for the peel ply, then let it go enough to have the rigidity in the bottom to shape the deck and then glass the deck as quickly as possible to gain some chemical bond to the lap from the bottom…sounds like a bit of watching & waiting to get it right!

I’m suprised no one’s mentioned this -

Have you ever tried sanding carbon or kevlar cloth??? I’ve no direct experience with carbon but worked with kevlar during my years at a boat builder and the stuff doesn’t sand well at all. It kind of frays, turns to fuzz. IMHO it’s not a good idea to have to do any extensive work on cured kevlar.

Also, are you aware of the problems of working with two adjacent materials of very different densities?? The soft foam will cut fast and the cured cloth won’t. Unless you’re using a power planer . Anybody tried hitting carbon kevlar with a power planer? Sounds like trouble to me.

Finally I’ve heard that carbon fiber dust is 10x itchier than regular glass dust which , to me, is bad enough.

I’m with Woody, why not shape it and glass as normal?

What kind of foam are you using? I’ve shaped 1 pound stringerless EPS foam. You need a light touch but it’s not necessary to have one side glassed .

Hello llilibel03 & thanks for adding your thoughts…

I believe that the bottom lap to deck when using the peel ply [from what i’ve read!] should end up quite smooth…& the deck glassing lap will not be carbon kevlar…so sanding should not be an issue.

I am very aware of the dual density sanding/shaping problems…but I wont need to touch the foam near the rail.

In answer to -

"I’m with Woody, why not shape it and glass as normal?

What kind of foam are you using? I’ve shaped 1 pound stringerless EPS foam. You need a light touch but it’s not necessary to have one side glassed . s."

As I said in my previous post…I need the bottom to have a hard skin as I’m shaping down onto it… i.e. taking the foam right out.

best advice i could give would be to make a miniature version to test your method first, I know the cloth is expensive but if you have the materials to make a scaled down version, you could hopefully evaluate any delam problems. This would also allow you to work out some of the other kinks before you make the actual boards.

Okay, good, now that I know where you’re headed. Speaking as a kneelo, I highly approve. Non-spoon-form flex kneeboards are something that works quite well and should be examined much further.

Right, shaping down to solid glass, you have several advantages. With a little sanding to roughen it up, plus maybe a quick application of a little fairly pure alcohol or acetone, you might well get a chemical bond, laminate to laminate. Allow the acetone/alcohol to evaporate completely, of course.

Uhmm- on the 7’3 and 7’6", I’d be cautious about leaving the center of the deck too thick, unless you’re willing to accept minimal flex there, and take it down to the center quite gradually. The reason being that you’d have a good chance of the laminate buckling free of the foam with a large separation/different radii/significant thickness in the bending area. Also, if the deck laminate is strong enough to resist buckling ( or it’s of something like a wide “U” section, with steep angles) it’d tend to resist flexing, maybe enough to act as ‘channel iron’ .

Interesting project. I look forward to hearing more as you go