When to coat wood?

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Fuzz
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When to coat wood?

Post by Fuzz » Thu Nov 24, 2016 11:34 pm

Most of us are not able to do all of our glassing wet on wet so we sand and then move on. One of the best ways to clean up and remove any amine blush is to wash with water. If you still have bare wood then no washing. So is it better to apply the tape and just sand it or apply the tape and coat the bare wood so you can wash the whole hull?



Browndog
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Re: When to coat wood?

Post by Browndog » Fri Nov 25, 2016 7:59 am

One of the reasons to precoat plywood with epoxy is to reduce the opportunity for scratches or dings in the surface veneer to occur. Not a real problem if painting or fairing the surface later, but a real issue with anything going to be kept in a bright finish. I'm fighting that now on a project where the plywood was not coated and scratches and dings in the wood are showing up regardless of the care that was used to try and prevent them. If working with dimensional lumber, not as much of an issue, because you can sand or plane the surface to remove the dings before finishing. With Marine plywood, the surface veneers aren't that thick.

I kind of prefer doing a light saturation coat of epoxy on the plywood and letting it cure then sanding prior to fiberglassing with light weight cloth. It will make it less likely to have resin starved areas on the glass and the glass cloth will tend to be easier to handle without catching on the grain and introducing runs when working on large surfaces.

On the other hand, I much prefer laying fiberglass tape on wet fillets or wet unthickened epoxy as it helps the cloth to adhere to a vertical surface, smoothes out the fillet or seam, reduces air bubbles under the glass and makes for a much neater finish. Sanding uneven hardened unglassed fillets is a pain in the rear.

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Cracker Larry
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Re: When to coat wood?

Post by Cracker Larry » Fri Nov 25, 2016 12:22 pm

or apply the tape and coat the bare wood so you can wash the whole hull?
This is what I prefer. My shop is open and a water hose is the best way to handle all the dust. I coat it once as soon as possible.
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Fuzz
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Re: When to coat wood?

Post by Fuzz » Fri Nov 25, 2016 2:06 pm

Cracker Larry wrote:
or apply the tape and coat the bare wood so you can wash the whole hull?
This is what I prefer. My shop is open and a water hose is the best way to handle all the dust. I coat it once as soon as possible.
Thanks Brown dog and Larry.

The reason for my question is the whole secondary bonding issue. If you do not coat it you have to protect the wood but you can get a primary bond to it when the time comes. If you coat it then you have the secondary bonding issue. I guess it bonding is not a big deal with epoxy given that the wood will be washed and sanded before applying glass to it :doh:

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Re: When to coat wood?

Post by terrulian » Fri Nov 25, 2016 3:02 pm

I'm with the those above on this. The strength difference between primary and secondary bonding is more for engineers than us common folk. Properly prepared, you will never have a strength issue with a physical rather than chemical bond.
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