epoxy bite to wood
 

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

Ron

epoxy bite to wood
 

Now it is time to lay glass.

Haven't had a wood/glass bond let go yet.

I take it that glass directly on wood doesn't hold well? Why doesn't it
adhere as well without glass as with?

epoxy bite to wood
 

"JS" writes:

I take it that glass directly on wood doesn't hold well? Why doesn't it
adhere as well without glass as with?

I don't have a clue. I described what works for me.

YMMV



--
Lew

S/A: Challenge, The Bullet Proof Boat, (Under Construction in the Southland)
Visit: http://home.earthlink.net/~lewhodgett for Pictures

epoxy bite to wood
 

JS wrote:
Now it is time to lay glass.

Haven't had a wood/glass bond let go yet.


I take it that glass directly on wood doesn't hold well? Why doesn't
it adhere as well without glass as with?

It is better to put down a coat of epoxy first to fill pores so they
don't drag resin out of the glass. Epoxy adheres to most plywoods
extremely well but a light 2oz scrim of glass keeps the face veneers of
the plywood from checking and makes a more stable surface for paint.

AS to the original question, it depends on what you plan to do but the
grit for birch is not all that critical. For a clear varnish top coat I
would sand to the birch to #120 grit, apply the epoxy and scrim, fill
the scrim and sand to #180 grit. If using a marine paint I would go to
#80 and #120 respectively then apply the recommended high build primer
and sand to what ever the paint system recommends.

You would need to stay with a coarser grit for tougher to bond woods
like white oak and teak because you have to rely more on the mechanical
surface bond.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

epoxy bite to wood
 

Glenn Ashmore ) writes:

You would need to stay with a coarser grit for tougher to bond woods
like white oak and teak because you have to rely more on the mechanical
surface bond.

I've read that the reason epoxy bonds well to wood is that it bonds at the
molecular level, the mollecules of curing epoxy being the same size or
something as the molecules of wood. So long as the surface of the wood is
clean and dry it doesn't need to be sanded for adhesion, except as noted
above in the case of woods with incompatible resins. Otherwise you only
sand if you want a smoother surface for the finish.

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epoxy bite to wood
 

epoxy bite to wood
 

On 8 Jul 2003 14:37:46 GMT, (William R.
Watt) wrote:

Glenn Ashmore ) writes:

You would need to stay with a coarser grit for tougher to bond woods
like white oak and teak because you have to rely more on the mechanical
surface bond.

I've read that the reason epoxy bonds well to wood is that it bonds at the
molecular level, the mollecules of curing epoxy being the same size or
something as the molecules of wood. So long as the surface of the wood is
clean and dry it doesn't need to be sanded for adhesion, except as noted
above in the case of woods with incompatible resins. Otherwise you only
sand if you want a smoother surface for the finish.


I don't think that is quite right, as in molecules bonding?
The word attraction, or resistance to surface tension, may be the
better term. - So you looking at wetting agents, and surface tension.

As in bonding, - would mean the epoxy is disintegrating, or migrating,
as in solution - which is want you wouldn't want.
What you would want is an ability to penetrating through the cell
walls. - As in its saturation ability.
In other words the chains can slip through the holes, and fill up the
cavities, so you wouldn't want, oils and waxs in the timber, but it
can take in a bit of water, so a small amount of water in the timber
as a wetting agent can help its movement.

If you try to separate two layers, you will see as it tears out the
fibers, as to its penetration ability - and you could test on various
formula -( lack of fillers ) As the timber is seen as just another
fiber type filler.
As for sanding, its not that big a deal, - but that's relative to the
saturation point of your mix - and any fillers then added.- the more
filler the more sanding, the less saturation.

epoxy bite to wood
 

I have found that if you REALLY want something to stick and it's
important, it will not stick. However, all those little drips and gobs
that seem to end up where you don't want them tend to be there
forever...go figure!!

epoxy bite to wood
 

epoxy bite to wood