Charles Spitzer wrote:


"Norm Dresner" wrote in message
...
"Dan White" wrote in message
...
Hi. I've been experimenting with different polyurethanes for my butcher
block counter tops and it looks like I'm settling on a Sherwin Williams
clear poly. I want a pretty high shine, but not the tacky gloss feel
and
uneven "liquid" look. My understanding was that I should sand the final
coat with maybe a 400 or even as low as a 220 grit, and then go up to
600
and higher depending on what kind of finish I would like. Tonight I
decided
to try wet sanding with 2000 grit on the clear gloss poly right off the
bat
instead of going through the paces of higher and higher grits (this is
on
a
test piece). It looks to me like it does fine. I have a nice smooth
finish
that has a little less gloss but is smooth to the touch and I don't see
any
imperfections. Am I missing something on my final 2000 grit finish by
doing
things this way? Might it be a better finish by going something like
400/600/1500/2000?

I sanded with 2000 on one half and left the other half of the sample
with
the high gloss "tacky" feel. When I put a wet towel down to clean off
the
sanding dust I noticed that the water beaded up on the untouched poly
while
it layed down on the sanded part. I can understand why this might be, I
suppose, with the micro abrasions on the sanded side, but I wonder if it
has
any impact on the resistance the finish has to liquids. After all, I'm
doing all this in order to protect the wood from occasional spills.

Any comments or ideas are appreciated.

dwhite


Sanding first with the very fine abrasive gives you a very smooth but not
necessarily flat surface that you'd get by leveling with the heavier
grits first.

isn't the flatness of the surface affected not by the grit, but by the
flatness and inflexibility of whatever is behind the sandpaper? the paper
would only take off the high spots if the backing was hard and already
flat.

However most people don't have the patience to flatten a surface with 2000
grit sandpaper. Sure, if it has a flat backing it will eventually get the
surface flat, but you may die of old age before the job is done. The grit
doesn't control flatness, but it does control cutting rate. The idea is
that you start off with something that cuts fairly fast, get the surface
flat quickly with that, and then use increasingly finger grits to take off
the marks that the coarse grit made.

AIUI surface tension is affected by the roughness of the surface so it's
not
at all implausible that your sanded side exhibits a lower surface tension
than the rougher side.

As long as you haven't sanded through the finish, you have the same
material
on both sides, though not necessarily the same thickness. My gut
reaction is that your finishes provide equal protection on both halves.

Norm


--
--John
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