"J. Clarke" wrote in message
...
George wrote:
OK, great. Now you've learned a bit about surface tension. Doesn't
mean
a thing as long as the film is continuous.
Points out something others are trying to say when they tell you not to
use
polyurethane. Any break in the surface is going to grow because
moisture
will use the same effect to slide between the finish and the wood, then
into the wood, promoting further separation of the two surfaces.
True for any finish, but the effect that he's seeing is called a "water
break free surface" and the main thing that it indicates is the the
surface
is free of oils, waxes, etc. Checking for water-break free is one of the
steps in adhesive bonding in many critical applications in aerospace.
Essentially he cleaned off any wax or oil that evolved during the curing
of
the finish.
That's interesting. I suppose that might also explain why the sanded part
feels smooth while the unsanded gloss poly feels sticky to the touch. Maybe
there are oils on the surface.
Poured some hot coffee on both surfaces today and wiped it up after about
1/2 hour. Both sides came clean although the sanded part looked like it
wasn't going to come clean at first. In no time it did come perfectly
clean. I couldn't find any hint of coffee. I also put a hot pot of coffee
on the poly for about 5 minutes. It looked fine. I did see what were
almost microscopic marks or bubbles when I removed the pot, but didn't have
time to see exactly what that was. I'm going to try that again tomorrow,
but things look good so far.
In a prior trial with Minwax, the coffee did penetrate to the wood but I'm
pretty sure that's because I didn't have enough of a build up of poly. I
suppose I'll have to live with the plastic wood look, but I think it is
better than leaving the wood to its own devices among the general public. I
figure I can always sand the poly off down the road if it starts to fall
apart for some reason.
dwhite
I can't see where that is any reason to use a less durable finish in a
situation that is going to be subject to a good deal of heavy use.
Makes thicker better, but of course, that promotes the "liquid" look.
"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
--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)
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