Sealing Plywood before Applying Epoxy

[Steve Bean]

My experience confirms the idea that pinholing is caused by air escaping from warm wood. I try to be sure the wood is cooling down when I apply epoxy. I am in agreement with thinning the seal coat.

[Terra Nova]

"Re: Sealing Plywood before Applying Epoxy"

On new construction my best tech is to vacuum or blow off the dust with compressed air or a bench brush or rag; then wash any teak surface using a paper towel wetted in acetone; then prime * everything using all the same WEST resin/hardener, wet on wet, over and over (especially plywood end-grain) until no surface will soak up any more; this might be only 1 coat, on some materials, but can be 1/2-dozen or more. Immediately the pre-cut/fitted (usually 24-oz bi-axial) material is carefully positioned, in place, right into the wet epoxy, quickly working it in with a squeegee. And then fully wetting out and saturating the mat, cloth, bi-axial..., and applying only enough resin as it requires for it to be fully (but just) wetted out.

*I avoid contaminating all surfaces and materials. This includes NEVER adding anything to thin or otherwise compromise the very best materials I can buy.

Sometimes additional layers can be applied immediately. Otherwise, if allowed to cure, a thorough sanding prep and acetone wipe is my choice.

Edit to add that, if any fairing is required, it is better to glass, first, then fair, for best adhesion.

[minaret]

Originally Posted by Terra Nova

Very bad tech.

From Gougeon brothers, themselves:
"Adding solvent is a quick, simple method of thinning epoxy, but unlike using heat to thin it, the strength and moisture resistance of the cured epoxy are drastically affected."

From:
Thinning West System Epoxy

You are just gonna keep quoting that article from 1999 we all read in the link back on page one, aren't you? Saying it over and over doesn't change what it says.

[HappyMdRSailor]

Originally Posted by minaret

Couldn't agree more with this practice, and you will note in the other thread about this which I linked to earlier, I was the only person who mentioned this concept. It makes a huge difference. And in fact, I have seen a half million dollar part sawn up and thrown in the dumpster because they refused to listen to me and did just the opposite.

Dang man... That is one helluva cockpit cooler....

Originally Posted by minaret

You are just gonna keep quoting that article from 1999 we all read in the link back on page one, aren't you? Saying it over and over doesn't change what it says.

I heard the best way to compute something was to feed some punched up cards into a slot.... walk around the other side of the building... and wait for your new set of punched up cards....

[Cheechako]

Having been Safety and Health Director at an aerospace firm I had to research MEK extensively as we were required to use it by specification for certain sealants related to the wing fuel compartments. If you do the research for how they test MEK for carcinogens, it takes a helluva lot of it to cause any issue at all. It's actually pretty gross; they inject rats directly with the stuff over a long period of time. They keep upping the dose in huge amounts until finally some of the rats succomb. The reality is you'd have to inject the stuff, and alot of it to ever show any increase in the cancer rate.

[Terra Nova]

Originally Posted by minaret

You are just gonna keep quoting that article from 1999...?...

The experts' opinion on this has not changed since 1999. My own boat building experience with WEST system epoxy began in 1976. My opinion has not changed since then, either.

Regarding the bubbles which form in the freshly applied coating, as the epoxy penetrates, air is displaced and expelled. This, regardless of temperature.

[minaret]

Originally Posted by Terra Nova

The experts' opinion on this has not changed since 1999. My own boat building experience with WEST system epoxy began in 1976. My opinion has not changed since then, either.

Regarding the bubbles which form in the freshly applied coating, as the epoxy penetrates, air is displaced and expelled. This, regardless of temperature.

In that case, can you give us a link to an example of one of these more recent "expert" opinions which states that their opinion is the same as yours? I doubt it, since even the one from '99 only appears to agree with you when you selectively quote from it.


If you heat the substrate first and coat it while its cooling, as stated above, there are no bubbles. Because the air in the interstices is contracting instead of expanding, which is what normally happens as the resin begins to exotherm, heating the air and causing expansion and hence bubbles instead.

[Terra Nova]

Min--if you know of a quotable source that contradicts my Gougeon brothers' quote, you are welcome to post it here. But I won't respond to further, unnecessary taunts.

[minaret]

Originally Posted by Terra Nova

Min--if you know of a quotable source that contradicts my Gougeon brothers' quote, you are welcome to post it here. But I won't respond to further, unnecessary taunts.

Nobody taunting you here. Just thought it strange that you would state that all expert opinion is the same as yours without a single link to back it up.

[minaret]

A few selective quotes of my own from the same article-




"Through knowledge gained from our comprehensive test programs and from 30 years of practical experience, we have learned that epoxy formulation is a balancing act. When one characteristic is altered-e.g. changing handling attributes by adding a volatile solvent-other characteristics like moisture resistance and strength are also changed. Our chemists formulate a well balanced, versatile epoxy that provides excellent structural strength and moisture resistance. If you elect to modify it, you become an epoxy formulator and need to understand the effects of your changes. Armed with the information in this article, you can decide if thinning epoxy is worth the tradeoff in performance."




"Does thinning epoxy make sense? In some situations, thinning is appropriate. In others, it is not. We feel that in most circumstances using heat to thin epoxy is preferred to using solvents. As long as the epoxy does not overheat during cure, the full physical characteristics of the cured epoxy remain. Adding solvent is a quick, simple method of thinning epoxy, but the strength and moisture resistance of the cured epoxy are signiflcantly reduced."

[minaret]

I suppose you also believe it's never appropriate to use products such as the aforementioned System Three sealer or Smith's/CPES either, as they are heavily solvent loaded epoxies?


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?

[minaret]

From Epoxyworks by WEST-


"Understand outgassing

Before coating bare wood, heat the wood and apply the epoxy while the wood is cool- ing. During cooling, the air in the wood con- tracts, drawing the epoxy in. The opposite happens if you coat wood as it’s warming (such as in the morning, in the sunlight, near a heater or anytime ambient temperature is rising). The air in the wood will expand and “outgas” while the wood’s temperature is ris- ing, resulting in bubbles in the curing coating."





http://ewmag.epoxyworks.com/ewmag/34...%20Coating.pdf

[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

[minaret]

Originally Posted by Terra Nova

Min--if you know of a quotable source that contradicts my Gougeon brothers' quote, you are welcome to post it here. But I won't respond to further, unnecessary taunts.

Still think I'm taunting you, or ready to come back with a response that doesn't include "I've been doing this longer so I must be right"? You still haven't addressed any of the actual points of my argument, other than to say that they are wrong.

[s/v Jedi]

What a manufacturer writes or which method they adopt as their "standard" one, is not to be taken as a religion, rather just a guideline that leads to a good result.

It doesn't mean that there aren't a hundred different ways to achieve that same good result.

When Minaret slaps on a sealer coat, that is just fine. Should have tested it but it's really hard to not get this right. I use the dry lay-up method which can probably lead to problems if not executed correctly, but I must say that I don't find it very hard at all and tests confirmed it's effective. Both methods get good results and which one to take is as much personal preference as one being more suitable than the other now and then.

Do the prep work: both methods require clean plywood and heating it improves results for both (any) methods