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Old 14-03-2014, 22:05   #1
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Sealing Plywood before Applying Epoxy

I'm building an icebox made of plywood, which I'm intending to glass using epoxy resin. Someone told me Pettit Old Salem 2018 clear sealer would be okay to seal the ply? Any thoughts on that? Or should I be using a specific laminating resin?
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Old 14-03-2014, 22:20   #2
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Re: Sealing plywood before applying epoxy

I've built several epoxy / fiberglass covered plywood boats. I've never heard of applying sealer first.

If you're going to varnish the plywood, then use a sealer first. No sealer is needed before epoxy resin.
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Old 14-03-2014, 22:47   #3
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Re: Sealing plywood before applying epoxy

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.
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Old 14-03-2014, 23:30   #4
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Re: Sealing plywood before applying epoxy

Sealing with anything other than the resin you are laminating with will keep the resin from bonding with the wood. Follow minarets advice.
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Old 15-03-2014, 00:50   #5
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Re: Sealing plywood before applying epoxy

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Originally Posted by roverhi View Post
Follow minarets advice.
In general, that seems to be a good idea! One of our very best sources of actual professional skill and advice. Now if he was only nearby with one of his giant grinders...

Jim
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Old 15-03-2014, 01:41   #6
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Re: Sealing plywood before applying epoxy

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In general, that seems to be a good idea! One of our very best sources of actual professional skill and advice. Now if he was only nearby with one of his giant grinders...

Jim



What, you guys need a repair?
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Old 15-03-2014, 03:43   #7
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Re: Sealing plywood before applying epoxy

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What, you guys need a repair?
Naahhh, mate, she's in good nick, but it is always good to have a nearby friend with a big grinder!

Hope your escape plan is on track!

Jim
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Old 15-03-2014, 04:36   #8
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Re: Sealing plywood before applying epoxy

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Originally Posted by minaret View Post
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.
Minaret.....what is MEK?
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Old 15-03-2014, 05:01   #9
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Re: Sealing Plywood before Applying Epoxy

M E K

Methyl ethyl keytone

A thinner
Very aggressive
Carcinogen has been known to cause
Cancer.
Will melt paints rubber plastic + more.
Epoxy will soften even after curing
Some times used to thin epoxy , I suspect
that will reduce bonding strength
Good for cleaning tools & brushes after use
with epoxy.
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Old 15-03-2014, 05:28   #10
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Re: Sealing plywood before applying epoxy

Quote:
Originally Posted by Jim Cate View Post
Naahhh, mate, she's in good nick, but it is always good to have a nearby friend with a big grinder!

Hope your escape plan is on track!

Jim
Jim,

I've said the same thing in a few posts here and there!!!

Currently thinking it would be great for him to show up with his foam shaper to "encourage" the kids into doing their schoolwork...
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Old 15-03-2014, 06:18   #11
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Re: Sealing Plywood before Applying Epoxy

Quote:
Originally Posted by BriaF View Post
M E K

Methyl ethyl keytone

A thinner
Very aggressive
Carcinogen has been known to cause
Cancer.
Will melt paints rubber plastic + more.
Epoxy will soften even after curing
Some times used to thin epoxy , I suspect
that will reduce bonding strength
Good for cleaning tools & brushes after use
with epoxy.
Also being highly reactive, MEK is a component of the older non-citrus gel type paint strippers, paint stripping dip-tanks, and solvent welding of plastics such as it's use in model airplane cement and acrylic to acrylic bonding.
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Old 15-03-2014, 06:18   #12
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Re: Sealing Plywood before Applying Epoxy

There is no need to thin epoxy and it will reduce the adhesive strength. Epoxy works because of a chemical balance - change it by adding another chemical (thinner) and you change the bonding, curing, and strength characteristics of the product. This is the base coat of your project and you don't want to see the next layers fail.
I often do a "hot coat" by warming the epoxy lowering the viscosity and while still "green" finish up the glass work. Don't heat the epoxy, but warm it to 80 - 85 degrees as well as the plywood. Remember, this will shorten the pot life and working time.
Here's some info - typical with most epoxies.
Good luck

http://www.westsystem.com/ss/thinnin...-system-epoxy/
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Old 15-03-2014, 06:29   #13
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Re: Sealing plywood before applying epoxy

Quote:
Originally Posted by minaret View Post
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.
Minaret,

I am interested but not entirely surprised to hear you say this. I want to say I have read at least one epoxy resin manufacturer advise specifically against thinning their product with any kind of solvent. In your experience this is fine? Did you ever do adhesion tests to compare thinned vs full strength?

Cheers
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Old 15-03-2014, 06:34   #14
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Re: Sealing Plywood before Applying Epoxy

Chenega brings up a good point: heating up the ply before applying resin. I had problems with "haze" showing up on my floorboards after coating them. This was apparently due to moisture (water vapor) trapped in the wood by the resin coating. Warming the ply would help to drive out the moisture and reduce this problem. Haze might not be an issue on the inside of an icebox, but I had to re-do my teak & holly veneer floorboards.
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Old 15-03-2014, 06:45   #15
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Re: Sealing Plywood before Applying Epoxy

I was gunna say "oh boy" a few posts ago....

I'm late....
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