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Epoxy theory....

Started by Smithkp, August 15, 2018, 01:46:39 PM

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Smithkp

I use a lot of epoxy to coat wood. I have this theory that if you encapsulate a board that has air dried, fully encapsulate it, will it crack, warp or rot? 

My brain says there will be no air exchange so moisture content will stay the same so no movement should be expected. But would it rot from the inside out? Doesn't rot require oxygen?

Very curious as to any answers one way or the other....
Anything worth doing is worth doing well.

Ianab

If wood is properly air dried it will have a moisture level well below 20%, which is what decay fungus or bacteria need to grow. So it won't rot unless water gets added.

But epoxy isn't 100% water resistant. It's still somewhat permeable to moisture, although it slows this down a Lot. So wood could still gradually dry out, and that could lead to warping or cracking.

So for that reason you want things properly dry before you apply any finish.
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low_48

Epoxy is also very sensitive to ultraviolet light. It breaks down after being exposed. Most boat people add a coat or two of spar varnish over epoxy to help out. So sooner or latter, it will crack, warp, and rot. No finish is forever.

Don P

Then, once a film forming finish is breached, if liquid water can get into the crack it will diffuse into the wood. That moisture has to leave as a vapor and most of the wood surface is covered by a good vapor barrier. Then the moisture content rises because more liquid water is coming in than can evaporate from the surface. MC rises into the mid 20% range and then you are in the rot zone.

I've seen something like this in log homes. If the wood is covered with a water repellant but breathable finish, a stain, it repels most bulk water but can also dry fairly readily. As long as the wetting events aren't too frequent that works.

Then there are those completely painted cement chinked 1920's log cabins that seem to survive. The ones that have I think have been kept very well painted. That encapsulation you are talking about has been maintained.

I had a client that applied stain to the heavily weathering south side of his logs annually. It refreshed the look but the buildup of stain became a film and in that full sun exposure the logs had working checks. The finish had many places to admit water and became a compost bag with the wet logs inside. I scooped out the inside of the logs in places by hand.

My feeling is that encapsulation is great until it inevitably isn't fully encapsulating, then its worse than nothing.

Smithkp

Quote from: low_48 on August 15, 2018, 09:31:10 PM
Epoxy is also very sensitive to ultraviolet light. It breaks down after being exposed. Most boat people add a coat or two of spar varnish over epoxy to help out. So sooner or latter, it will crack, warp, and rot. No finish is forever.
I use an epoxy with a UV inhibitor for anything going outside. I made a cedar picnic table 2 years ago and the epoxy has locked in the colors of the cedar and it hasn't turned grey and it still looks like the day I applied it.

 
Anything worth doing is worth doing well.

Weekend_Sawyer


 That is a very nice looking table.

Here is a tip, when you view your pictures in your gallery there is a crop and rotate button.

Jon
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samandothers

This discussion is help full. I am looking to put someing on a wood top vanity.  Have considered epoxy.  Some others have suggested shellac or Waterlox.  Two of these I believe would encapsulate.  I believe the Waterlox would penetrate.

Decisions decisions.

Don P

All three are film forming finishes. Waterlox is basically thinned varnish.

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