What is a proper grit to prepare "A" faced ply (birch if it makes a
difference) for epoxy coating prior to painting.

You could sand the surface with something im the 180 - 220 range, maybe even
coarser, but if the surface of the wood is natural, clean and smooth, I believe
you will get a good bond between the wood and the epoxy even if you don't sand.

Almost all my experience is with the Gougeon brothers WEST System epoxy
(http://www.westsystem.com/). However, I believe several of the other epoxy
systems are similar. WEST was developed initially for coating wood surfaces..
the WEST stands for something like Wood Epoxy Saturation Technique.

On plywood or wood, I have put two or three coats of WEST epoxy on. You can
either put on the second and third coats once the previous coat is hard enough
not to run, or you can wait until it cures and sand it. This sanding is both
to get a good bond between the epoxy coats and to smooth the surface for the
next coat. I believe the WEST system literature says that if you recoat within
24 hours you do not need to sand the previous coating.

I believe that if you are coating the surface while it is horizontal, you may
be able to get a thicker coat on without it running, and get away with only one
or two coats.

The instructions that come with the paint you are using should tell you how to
prepare the epoxy surface for painting. Normally I would let the epoxy cure,
and perhaps leave it a few days to be certain I have a complete cure, then sand
with something in the 220-400 range to get a nice smooth surface but with some
texture for the paint to stick to.

Some epoxies, under some circumstances, get a coating called amine blush as
they harden. You are supposed to wash and or sand this off before putting any
more epoxy or any paint on the surface.

Good luck,

Alexander Meller

So many ways to do the same thing reinforces my experience that epoxy is
hard to screw up.

Thanks for all he replies.

Regards, Ron

PS to Scotty, I'm only going to epoxy coat the outside and just paint
the inside. I think that will overcome our mutual concern about
encapsulation.

(Backyard Renegade) wrote:

I guess I was more trying to make a point with my simple terms. That
point being, I always take an extra minute to rough the surfaces up
too, especially in structural areas. For areas that will be hidden in
a joint or filled later I use two tools for roughing. One is a heavy
grit offset grinder and when I can't get that in there or for more
precice work I take an old jigsaw blade, add a little bend and draw
the blade over the surface in a cross hatch pattern. And just to take
it one step further, I always mix up a small batch and throughly wet
each surface then add filler to the rest of the batch and paint or
spread it on the wetted surfaces then fasten or clamp.

I have always reccomended using as little filler as necessary to hold
the goo in place. A lot of my construction calls for epoxy to act as
as adhesive (glue?, simple terms again) as opposed to just filler for
glass... I have always explained it as "let the epoxy do what epoxy
does"... anyway simple terms again, but now I have a better
understanding as to how it works.
Thanks, Scotty

I read all these sort of things years ago when I started using epoxy
and so I did some tests. I made a series of lap joints where the lap
was four times the thickness of the wood. I used mahogany, red oak,
and fir. I made pieces planed smooth, fine sanded, rough sanded, and
rough sawn. Finally, I tried tight clamping, and loose clamping. I
did coat the pieces with unthickened epoxy and allowed them to soak up
for 10 minutes before adding thickened epoxy and clamping. I was
surprised and pleased to find that in all cases the joints were
stronger than the wood.

After having accidently left a block of wood next to a puddle of
penetrating epoxy (Syatem Three Clear Coat) one day, I found the next
day that it was bonded to my work bench. So I experimented and found
that I could even make a good joint by clamping pieces of smooth and
flat wood together dry and dribbling Clear Coat on the edge of the
joint, letting it suck in by surface tension.

So, using clean wood and good epoxy, well mixed, I don't worry about
how smooth the surface is as long as I have full contact in the joint.
With glass over pre cured epoxy, it generally has to be washed to
insure you don't have an amine blush which will interfere with
bonding. Sanding won't remove the blush, only spread it around unless
you remove the whole surface. The same care should be taken with any
epoxy joint over pre cured epoxy.

Al

How's the boat coming, Al?
Darn, I like that design.

Jim

Al Gunther wrote:
snip

"Alexander A. Meller" wrote:

What is a proper grit to prepare "A" faced ply (birch if it makes a
difference) for epoxy coating prior to painting.


-----

I have often wondered if plywood surfaces aren't contaminated with the glues etc
used to manufacture the plywood. If so, I would assume a solvent wash and or
sanding would remove? Anyone have an idea on this?

Also, how about adding say 10% solvent the the first coat of epoxy (either with or
without the cloth) to aid in penetration of the epoxy into the wood.

Paul Oman
www.epoxyproducts.com/marine.html

"Paul Oman" wrote in message
...
I have often wondered if plywood surfaces aren't contaminated with the
glues etc
used to manufacture the plywood. If so, I would assume a solvent wash and
or
sanding would remove? Anyone have an idea on this?

When building a 10ft lapstrake dinghy, I mostly wiped the surfaces with a
solvent. But many times I didn't, but never experienced any problems.

Also, how about adding say 10% solvent the the first coat of epoxy (either
with or
without the cloth) to aid in penetration of the epoxy into the wood.

Don't. You thin the epoxy, thinner evaporates and leaved thinned porous
epoxy behind. Normally, epoxy penetrates the wood sufficiently, especially
at higher environmental temperatures. If you really want good penetration,
heat the wood first and then, while cooling down, apply the epoxy. It gets
warm and thin and get sucked because the trapped air in the wood contracts.
Do not heat the wood when the epoxy is applied. You'll get a lot of air
bubbles.

Meindert

Ron Thornton wrote:
: What is a proper grit to prepare "A" faced ply (birch if it makes a
: difference) for epoxy coating prior to painting.

: Ron


Be careful regarding your choice of paints; I did the above
with epoxy then interlux bright-side (brite-side ??) IT DID NOT DRY.

Call to interlux tech support said that the epoxy posioned the
interlux drying catalyst. The guy's rec was to scrape it all off;
I didn't and it is now 4 months later dry enough to be useable.
(after all, you don't
need a catalyst for a chme reaction if you are willing to wait!)

Note: I did clean off the amine using h2o, detergent and de-waxer.


--

almus kenter
`` Pluralitas est ponenda sine neccesitate''