Epoxy coating plywood question?

The hull stringers are 3/4"x2" or 3" (forget which) Doug Fir about 8" to 10" apart.

Would you recommend cutting the Kevlar to fit between the stringers or run it up & over them?

If I run it up & over them, I'll make small filet at the ply and stringer junction and radise the inward facing edges of the stringers so aren't any sharp corners for the Kevlar to try and conform to.

If there isn't a problem with wrapping the stringers, I may as well do so. I guess it would tie everything together. It would mean a little less cutting and fitting and won't really add much weight at all.

Also unless it would be a problem or you recommend against it, I'll cover the 5oz Kevlar fabric with Kevlar tissue/vail fabric to smooth the weave and will also use peel ply over most all fabric layups.

I'm surprised more people don't use peel ply fabric. Especially when using Xynole, with it's little fuzzies after wet out coat. The reduction in excess resin and less sanding is worth the little extra cost.
For composite homebuilt aircraft building it's SOP.

Cheers, Allen

 

Peel ply is great. Used it on both hulls and all cross beams.

 

What brand did you use & who did you purchase it from?

Cheers, Allen

 

you have wrong info on solvent thinned epoxy. Used to be most epoxies were solvent thinned. A number still are. After almost 30 years in the epoxy business I am becoming a bigger fan of solvent thinned epoxy every decade!

paul
progressive epoxy polymers inc

 

Perhaps, I'm out in left field with this, but what if the Kevlar was applied under the stringers? Applied to the ply panels before being attached to the framework. I'm not sure of your construction method.

 

LP, good idea, I wonder if there would be any problem with applying the Kevlar to the plywood first?

She has 4 bulkheads with 5 - ¾"x3" stringers. Butt blocks of plywood go on inside of vertical seams between stringers.

Could tape vertical seams with Kevlar before bonding butt blocks.

Anyone, would this work?

Probably need to pre bend the end pieces before putting Kevlar on them. Might not bend well after Kevlar is put onto plywood.

Cheers, Allen

 

This is a good idea, if you can bend the panels in place with the Kevlar bonded on, maybe while the goo it still green.

 

Actually that's a good idea PAR.
I'll dry fit the panels and mark where stringers are so can apply epoxy in correct place on panels.

Will have locating screw holes for alignment. I guess no reason to let the Kevlar/epoxy go past green cure, so will still be able to flex a little to conform to hull stringers curve. Plus with a bit of curve in the panel before laying the Kevlar. It's not compound bend.

Probably predrill ply panels for screws that hold ply skin down till epoxy sets. Be easy to keep spacing even & not splinter the ply face in joint.

This should work then as long as screws don't twist Kevlar as they go through. But the should push between the fibers of the Kevlar cloth I would think. They don't need to cut the strands to penetrate the cloth.

I guess I'll test it first to make sure! Lol

I'm guessing not but thought I'd ask just in case..
There's no problem having a laminate of plywood, Kevlar & Douglas Fir as far as bonding strength is there?

Cheers, Allen

 

Nope . . .

 

The system 3 clear coat from what I understand is just epoxy thinned with xylene?

 

Tungsten, I don't think so. ThieSystem Three web site says no volatile organic compounds in Clear Coat Resin. Xylene is a VOC.

But that's the extent of my info so far! Lol

Cheers, Allen

 

System Three Clear Coat resin system hasn't any Xylene in it. It uses non-reactive viscosity modifiers to lessen it's thickness and though still an amine hardener, these modifiers reduce blushing dramatically.

 

As an aside, there is some very noxious thinner th system three silvertip. Great stuff for hand lamination... quite thin, wets out quickly.

But that sweet smelling thinner can really get to you in confined spaces.

Anyone know what that is? Not one of the normal solvents.

 

Well its good to know,the clear coat here in Canada is 3 times the price of the Silver tip which is twice the price of some of the lesser known brands.

 

epoxy questions? email me at info@epoxyproducts.com


paul oman
progressive epoxy polymers inc.