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wrote in message . ..
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.

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