primary v secondary bonds

[hokeyhydro]

Okoume ply is rather soft skinned, and it is tempting to precoat parts, but then one must wash amine blush off and sand to epoxy them together. Now I have peel ply, and using that on a precoat, if peel ply works as advertised, eliminates those tasks. Peel it off, ready to recoat. But that would create a secondary bond. When i do the stitch & glue thing I coat raw wood with neat epoxy, proceed to apply fillet goo, radius it out, and soon as fillet goo is stiff enough, lay on glass tape and epoxy. That creates a primary bond.

So my question is: if I use peel ply over a precoat, then peel it off and proceed to do the S&G thing, is the secondary bond formed adequate or suspect?

Of course there are joints which are not heavily stressed which I would consider non-critical where a secondary bond is good enough. At least numerous secondary bond joints held up on my outboard race boats with no fails. But other joints, say the chines of an S&G hull are kind of critical, so if anyone has doubts about using a secondary bond there please shout out.

Yes, I will do test pieces which I will intentionally destroy, although my test "instruments" are not scientific quality.

Bill

P.S. precoating hull skins is not a good plan because after the epoxy kicks and cures the skins may be too stiff to assume the curves intended by the designer. I'm talking precoat of flat panels AKA bulkheads and the like.

[PAR]

You still have a window of opportunity to get a chemical (primary) bond with peel ply. Each brand is different, but you should be able to pull the peel ply as soon as it's possible without lifting the coating, but while the epoxy is still "green" For most epoxy formulations this is within 12 hours, but the sooner then better, so you'll have to experiment with you brand and the conditions you're working in. Pre-coating panels usually doesn't make them too stiff to conform to the usual radiuses employed in taped seam builds. Again, if you can bend the panel in place while the poxy is still green (dry to the touch, but dentable), the bend will be easier.

[Peter HK]

If done correctly a secondary bond is still stronger than the ply, so there really is no issue. I've tested plenty of them and the wood fails first.

Cheers

Peter HK

[hokeyhydro]

PAR - yes, I know working with green epoxy is good, but with my crazy variable shift schedule working Aircraft Rescue at our regional airport my boat building windows are scattered, so I usually don't have the opportunity to keep on rolling on a build.

Peter HK - As I mentioned my outboard race boats which traveled at high speed with plenty of twisting stress were loaded with secondary bonds and I never had a failure. I am including secondary bond in my test pieces when I experiment with various fillet combos, but I suspect they will pass, as in wood explodes before glue joint.

[John Burritt]

Maybe I'm missing something, but aren't you trying to make a complicated job out of a simple one? Okoume is not so soft that it can't be installed before coating.

[hokeyhydro]

Maybe I'm missing something, but aren't you trying to make a complicated job out of a simple one? Okoume is not so soft that it can't be installed before coating.

If one is careful, damage can be avoided. What I would like is precoat so there is less meandering around all the itty-bitty parts with brushes and/or rollers to coat the interior. A nice coat while parts are flat and loose strikes me as easier.

[Howard]

Seems to me you are not talking about the main body of the flat areas, but rather the edges of panels where the fillets and tape will be? Why not cover those edges with an appropriate width of plain masking tape.......my preference is the blue stuff......and once you have rolled on your 3 or 4 cover coats.....green on green......lift the edge tape off, leaving bare for your edge?

You could even pre-sand them before you install them.

[Charlie Jones]

My thoughts also. Or simply don't coat about 3 or 4 inches of the edge that will be taped.