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14-03-2014, 21:05
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#1
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Registered User
Join Date: Jun 2012
Location: Toronto ON
Boat: Morgan 33 O/I
Posts: 51
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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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14-03-2014, 21:20
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#2
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Registered User
Join Date: May 2011
Location: Miami Florida
Boat: Ellis Flybridge 28
Posts: 4,057
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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.
__________________
Retired from Hopkins-Carter Marine Supplies
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14-03-2014, 21:47
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#3
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Resin Head
Join Date: Aug 2007
Location: Seattle WA
Boat: Nauticat
Posts: 7,205
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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.
__________________
O you who turn the wheel and look to windward,
Consider Phlebas, who was once handsome and tall as you.
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14-03-2014, 22:30
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#4
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Moderator Emeritus
Join Date: Aug 2005
Location: Carlsbad, CA
Boat: 1976 Sabre 28-2
Posts: 7,505
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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.
__________________
Peter O.
'Ae'a, Pearson 35
'Ms American Pie', Sabre 28 Mark II
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14-03-2014, 23:50
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#5
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,151
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Re: Sealing plywood before applying epoxy
Quote:
Originally Posted by roverhi
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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
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Jim and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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15-03-2014, 00:41
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#6
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Resin Head
Join Date: Aug 2007
Location: Seattle WA
Boat: Nauticat
Posts: 7,205
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Re: Sealing plywood before applying epoxy
Quote:
Originally Posted by Jim Cate
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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What, you guys need a repair?
__________________
O you who turn the wheel and look to windward,
Consider Phlebas, who was once handsome and tall as you.
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15-03-2014, 02:43
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#7
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Moderator
Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 21,151
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Re: Sealing plywood before applying epoxy
Quote:
Originally Posted by minaret
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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 and Ann s/v Insatiable II, lying Port Cygnet Tasmania once again.
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15-03-2014, 03:36
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#8
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Registered User
Join Date: Nov 2008
Location: Hobart Australia
Boat: Catalina Morgan 45
Posts: 350
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Re: Sealing plywood before applying epoxy
Quote:
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.
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Minaret.....what is MEK?
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15-03-2014, 04:01
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#9
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Registered User
Join Date: Mar 2012
Location: Aus
Boat: Owner Builder
Posts: 115
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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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15-03-2014, 04:28
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#10
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Moderator Emeritus
Join Date: May 2008
Location: Fort Lauderdale, FL
Boat: 48 Wauquiez Pilot Saloon
Posts: 5,975
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Re: Sealing plywood before applying epoxy
Quote:
Originally Posted by Jim Cate
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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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...
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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15-03-2014, 05:18
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#11
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Registered User
Join Date: Oct 2011
Posts: 3,604
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Re: Sealing Plywood before Applying Epoxy
Quote:
Originally Posted by BriaF
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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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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15-03-2014, 05:18
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#12
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Registered User
Join Date: May 2012
Location: CT
Boat: Corbin 39 / 41.5 LOA
Posts: 262
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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/
__________________
Live the dream, life is good
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15-03-2014, 05:29
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#13
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Registered User
Join Date: Oct 2011
Posts: 3,604
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Re: Sealing plywood before applying epoxy
Quote:
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.
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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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15-03-2014, 05:34
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#14
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Registered User
Join Date: Mar 2011
Location: Southport CT
Boat: Sabre 402
Posts: 2,712
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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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15-03-2014, 05:45
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#15
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Moderator Emeritus
Join Date: May 2008
Location: Fort Lauderdale, FL
Boat: 48 Wauquiez Pilot Saloon
Posts: 5,975
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Re: Sealing Plywood before Applying Epoxy
I was gunna say "oh boy" a few posts ago....
I'm late....
__________________
In the harsh marine environment, something is always in need of repair...
Mai Tai's fix everything...
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