Sealing Plywood before Applying Epoxy

[Weyalan]

Originally Posted by minaret

I always seal before glassing. Use the epoxy you will laminate with heavily reduced. I like 25% MEK or even more, but be sure you are using a slow hardener and catch the chemical bond window. Never seal with anything but the resin you will be laminating with.

We have done a lot of construction / refit with plywood and fibreglass.

We usually pre-treat the plywood (especially end grain) with Wattyl 2-pack timber preserver before applying fiberglass & epoxy resin (R180): Is this the wrong thing to do?

[minaret]

Originally Posted by Weyalan

We have done a lot of construction / refit with plywood and fibreglass.

We usually pre-treat the plywood (especially end grain) with Wattyl 2-pack timber preserver before applying fiberglass & epoxy resin (R180): Is this the wrong thing to do?

Couldn't tell you; never heard of Wattyl and don't know what sort of resin you are using.

[Weyalan]

Originally Posted by minaret

Couldn't tell you; never heard of Wattyl and don't know what sort of resin you are using.

Wattyl is an Australian paint manufacturer
The timber preserver is a two pack polyamide cured, epoxy clear sealer
http://www.wattylindustrial.com.au/d...0TP80%20v4.pdf

R180 is a commonly used (in Australia) 2-pack epoxy resin
http://www.amcsupplies.com.au/data_f...180%20MSDS.pdf

[minaret]

Originally Posted by Weyalan

Wattyl is an Australian paint manufacturer
The timber preserver is a two pack polyamide cured, epoxy clear sealer
http://www.wattylindustrial.com.au/d...0TP80%20v4.pdf

R180 is a commonly used (in Australia) 2-pack epoxy resin
http://www.amcsupplies.com.au/data_f...180%20MSDS.pdf

Well, it's a polyamide which means it's a true epoxy. Should be fine. I note they recommend thinning the first coat 50% and the second coat 25%. I note they recommend sealing to "eliminate ingress of moisture" and "reduces risk of warping and dry rot". But as I've said, never used it. So I don't really know.

[HappyMdRSailor]

Look out! I got my learnin' cap on! School's in session....

Originally Posted by minaret

Can you explain why Interlux 2000e, an epoxy which is also heavily solvent loaded, is a superior moisture barrier to neat WEST? How does that fact jibe with what you are saying?

Originally Posted by minaret

Article about stiffness and lack of elongation causing brittleness in WEST epoxy. Obviously a slightly more flexible epoxy is good for a sealer coat on wood, and G Flex and Six-Ten are both more flexible products than original WEST. Wonder why they did that?

http://ewmag.epoxyworks.com/ewmag/25...g_Flexible.pdf

Min.... Are you saying that 2000e is better for a barrier coat than unthinned epoxy??? Because of the flexibility of the coating???

Ok Professor... your turn!

[minaret]

Originally Posted by HappyMdRSailor

Look out! I got my learnin' cap on! School's in session....





Min.... Are you saying that 2000e is better for a barrier coat than unthinned epoxy??? Because of the flexibility of the coating???

Ok Professor... your turn!

No, it's a better barrier because of "micro plates". The filler in it is made up of extremely fine flakes of highly moisture resistant material in suspension. When applied, the micro plates all align in plane with many many layers of overlap, like shingles on a roof. Water has to get between the plates to get through. It's never as simple as they'd like to make it seem, there are many factors to consider in moisture resistance. Pin holing from solvent off gassing is just one fairly minor consideration.

[HappyMdRSailor]

Originally Posted by minaret

No, it's a better barrier because of "micro plates". The filler in it is made up of extremely fine flakes of highly moisture resistant material in suspension. When applied, the micro plates all align in plane with many many layers of overlap, like shingles on a roof. Water has to get between the plates to get through. It's never as simple as they'd like to make it seem, there are many factors to consider in moisture resistance. Pin holing from solvent off gassing is just one fairly minor consideration.

Dang that sneaky filler!!!

Make perfect sense... Sounds like well engineered product...
Thanks for the learnin' Teach!

[minaret]

Originally Posted by HappyMdRSailor

Dang that sneaky filler!!!

Make perfect sense... Sounds like well engineered product...
Thanks for the learnin' Teach!

Wouldn't use anything else on a bottom. Anytime!

[Delancey]

Originally Posted by minaret

extremely fine flakes of highly moisture resistant material in suspension

Very interesting. Just a wag but I'm guessing said flake-pigment is milled down from a partially cured epoxy solid material. One of the two parts of the paint system reacts with the partial-cure pigment so the whole mess cross-links into a single polymer and in so doing works works around the solvent-tunnel issue by creating a shingled roof barrier of non-solvent affected epoxy solids. Kinda sorta like a Pre-preg material. That's my theory anyway.

[s/v Jedi]

Originally Posted by Delancey

Very interesting. Just a wag but I'm guessing said flake-pigment is milled down from a partially cured epoxy solid material. One of the two parts of the paint system reacts with the partial-cure pigment so the whole mess cross-links into a single polymer and in so doing works works around the solvent-tunnel issue by creating a shingled roof barrier of non-solvent affected epoxy solids. Kinda sorta like a Pre-preg material. That's my theory anyway.

The micro plates are mica material

[Delancey]

Originally Posted by s/v Jedi

The micro plates are mica material

Makes sense, as far as making tiny flakes goes. Better than my dumb theory.

[HappyMdRSailor]

Originally Posted by s/v Jedi

The micro plates are mica material

micro mica = micra???

Originally Posted by Delancey

Makes sense, as far as making tiny flakes goes. Better than my dumb theory.

Hey now!

I personally liked your "not-dumb" theory!

[Lojanica]

I like Miaret's idea of sealing the unfinished ply with the same epoxy thinned by 25% with Xylol (tolulene).

Another trick I found surrendipiditously when I had wood that was infested but I needed to use it anyways was to mix boric acid in hot ethylene glycol. It was amazing the wood soaked it up like a sponge. It then needs to sit for a couple weeks to dry out. Then light sanding with a stiff grit then apply unthinned epoxy.

This will not rot. I wouldn't do it for a structural application but for a box or something you wanted to last but wasn't too worrried about strength like a deck box or inside cabinet or a big timber where the timber gives strength ---bowsprit but not for cold molding a hull for instance.

[Ketchgould]

I built an icebox a year ago. I didn't gave to glass the plywood only the foam that was inside the plywood shell.