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
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.
I can't speak to the question at heart as I don't use the poly stuff. Have
you considered other finishes that are a bit easier to repair? Kitchen
countertops will no doubt see a good number of "accidents" and you may want
to consider the possibility of having to re-finish/touch up areas down the
road. My understanding is Poly is a very tough finish but repairing it is
This is a commercial application and the counter will be subject to
occasional water/coffee spills and I needed something that would provide the
best protection from stains. The areas that will contact food will have
mineral oil on it.
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.
Makes thicker better, but of course, that promotes the "liquid" look.
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
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.
Reply to jclarke at ae tee tee global dot net
Regardless what you call it, if you have scratches in the surface, you won't
get a tight droplet, and particles like those in coffee will hide from a
swift wipe like troops in foxholes.
Now your experiment in using your surface as a hot plate is another matter.
"Microscopic bubbles" is a red flag. You might be evolving excess moisture
from beneath, and this will break your finish from the wood..
I'd bet on uncured vehicle, that's for sure. Week or more for full cure.
For repairs You'd have to do the entire, or see the edge. You might blend
it flat, but it'll show a shadow.
Maybe there is still some
No. The only reason to use more abrasive grits is to more quickly knock
down areas. If your application is smooth enough that you can achieve the
desired smoothness with only 2000 grit, then don't go any more abrasive -
you're just making more work by doing so and removing finish for no good
As long as you don't go through the finish - which is unlikely with 2000
grit, then you are not at any risk with what you see. You just don't have
the same surface tension as when the scratches weren't there. If it really
starts to bug you then go get a quart of automotive buffing compount (light
cut) and buff it up with that. It should take the fine scratches from the
2000 right out with a bit of elbow grease.
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
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.
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.
Reply to jclarke at ae tee tee global dot net
Yes, but generally not smooth flat. There will typically be lots of
inconsistencies in the surface. Everything from brush strokes if you use a
brush to differences from the lap if you spray it, or even orange peel.
Dust finds its way in sometimes and the less than perfect surface of the
wood will telegraph in the finish. All of this - or any of this adds up to
a less than flat surface. Depending upon how irregular it is, you will
select a grit to take it down and then progress upwards in grit to be rid of
the sanding marks. With sprayed finishes it's not uncommon to be able to
start no coarser than 1000 grit. Typically, you can go to 1200 or 1500 from
there and then to a fast rub with a rubbing compound for a mirror finish.
In essence, flat is what you want to define flat to be. For some, nothing
less than a mirror finish is flat. That absolutely calls for sanding.
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