Lots of good and bad information here. I do this for a living, but as alwa
ys, your mileage may vary. Just some random thoughts:
Good post DadiOh. Dr. Marlow, don't confuse that high powered ultra hot sp
ecialized poly you shoot with the big box stuff going on a home project app
lied with a paint brush. With your experience and skill level in auto pain
ting (a highly technical field when done right) you might be thinking the o
ff the shelf products the average guy uses perform as well as your stuff.
For example, I sometimes shoot a pre catalysed polyurethane conversion lacq
uer that you can recoat in 20 minutes and get full adhesion, no sagging and
no witness lines! Try that with Minwax, Bartlett's, General Finishes, ML
So, here's my take. To anyone reading this, remember what you paid for it.
I don't sand between coat of poly unless it is to remove a nib or drip. NE
VER. If you recoat when you should, you don't need to. I have never had a
finish fail. Sand if you need to, but it isn't required. I have sanded be
tween coats and it has caused me more heartburn that it is worth. Practice
your application, learn your product carefully and you won't have to do it
Using soap to sand between applied coats of anything but more soap is folly
. Why would anyone use a surfactant product that is loaded with perfumes,
dyes, oils, silicone and other chemicals to sand? This is an enormously ea
sy way to foul your finishes. If you must sand, buy non-stearated paper to
use. Steel wool has oils in it, and even the ones that don't will tend to
break off the fibers (as designed) and leave them behind on your finish.
If you cannot find non-stearated paper, find the very finest Scotch Brite p
ad you can get (white?) and use that.
You don't need more than three coats of poly. Each coat should be applied
at a uniform 3 mil thickness, which will dry to a thickness of about 1 mil.
(This is based on a precat product with 25 to 30% solids). Three coats w
ill give you a final build of 3 mil, which is great for most tables, furnit
Wear resistance is not based on final product thickness. Additional coats c
an make the final product discolor more easily, and since it is not applied
as designed, in come cases make it unstable or brittle. Wear resistance i
s based on proper application as specified by the manufacturer that designe
d the product, and the quality of the resins used in its manufacture.
I have not put on a poly finish in years (remember Mike... not your stuff)
that doesn't require 21 days as the magic number for full cure. Yes, green
cure is in as little as 48 hours, but full strength isn't for much longer
The longer the finish has to cure, the harder it will be as all chemical an
d physical actions/reactions will have ended. The harder the finish is, th
e easier it is to "rub out".
Putting wax on polyurethane is silly unless it makes you feel better. A pol
yurethane is nothing more than a modified plastic polymer, so you are waxin
g plastic. Certainly the wax provides NO value to the protection of the wo
od. Waxing can lead to build up of wax residue, and improper application (
say at the wrong time) can foul your finish.
As a finish dries/cures, it shrinks. It will flatten on its own, without a
ny fuss. This is easy to see; how do you think your brush marks disappear?
Why do you think your lap marks reduce or disappear? The last Minwax app
lication I did for a table top I applied with a lamb's wool applicator and
every single ridge and valley disappeared. All of them. You can also see
this when you put poly on an unfilled wood like oak, or fill a rough spot i
n a board. You fill them when you apply, then come back later and the prod
uct that filled the holes in the oak and shrunk back, the tension is broken
and the holes in the oak are readily seen. Filling a board with planer ch
ip out around a knot will look good until the product dries, then you will
see the chip out very easily. This is why you pore fill, and fill divots.
The product shrinks and tightens up. It does not sag or relax to fill imp
As pointed out by Ed P, you can get an incredible finish that would make an
y furniture maker proud using poly if you are willing to put the work into
it. For years, Jeff Jewitt had a great picture on his web site of his bran
d of poly (Target)sitting on a table. He did as Ed described, and the refl
ection on the table that used his poly and that method made a mirror like f
inish that reflected the poly can perfectly. Really nice. It could easily
be confused with a rubbed lacquer finish.
There is a lot of great information out there that can be easily had. Here
is a great primer on polurethane:
Use articles from credible finishers as your guidelines and do what works f
or you after you try out their advice and tips. By the way, Bob Flexnor wr
ote the above referenced article; if he says it, you have a 99% chance of b
eing able to take it to the bank. My finishing got noticeably better after
I read absolutely everything I could find that he wrote. The man is a mast
er of PRACTICAL finishing techniques.
Mr. Marlow and I have talked about this aspect, too. It is soooo easy to c
all the manufacturer of a product and ask them any questions you have. Why
rely on a bunch of guys you don't know? You might be getting advice from
a guy that applies finish to a project every six months or longer, and uses
product that is a couple of years old. That won't yield anything good. E
very can has a tech support number these days and usually a tech guy on the
ready. I call whenever I have a question about anything to do with their
products and the manufacturers have always been glad that someone took the
time to call them before starting their application as opposed to calling a
fter they screw it up.
Good luck. Remember, practice on your scraps, not on your projects.