Life has gotten busy and my bookcase project has slowed to a crawl.
But I managed to get three coats of wiping poly on two face frames
this weekend. I used satin poly cut roughly in half with mineral
spirits. I like the look. Does that mean I'm done? Oh I'll probably
rub them down in a few days, but what I'm asking is if there's any
reason to add more coats (for protection?) at this point if the "look"
is already what I want.
Wiping varnish is thin naturally and three even more thinned coats doesn't
afford much protection; however, a bookcase doesn't *need* much protection
so stop when you like it.
FWIW, I figure four coats of unthinned oil poly for floors, three for
anything else that gets some wear. With brushing lacquer I usually use
three, sand heavily and then two more. For outside stuff with alkyd
Yeahbut.... thin is thin. Does it make any difference whether you
thinned it or MinWax did? Granted, you may not have thinned it as much
(or maybe you thinned it more), but when all's said and done, you've
wiped on a thinner coating than you'd have laid on with a brush or spray.
As Lew says, go with your gut. Frinstance... I finished an 8/4 solid
oak surround for a bar top (think frame with the field being ceramic
tile) ~ 27 yrs ago with a gel satin poly varnish. I gave it, IIRC, 3
coats with light steel wool and tack cloth in between coats 2 & 3. This
was followed up by a re-coat, with MinWax wiping poly a year or so ago
simply because I was touching up another piece in close proximity.
Didn't need it but the whole shebang looks as it did when I first
So many variables come into play with your project (and all projects,
really). Is it going to be exposed to direct sunlight? Are you using
it or are the kids? etc.
In any event, if you think you're done with the face frame and sides,
you're probably not quite done with the top of the shelves (think wear
IOW, go with your gut and common sense<g>
On Sunday, March 17, 2013 9:41:13 PM UTC-7, Greg Guarino wrote:
After the second coat you have a finish that will last a lifetime unless it
is a bowling ally or highly used table top or other high traffic surface.
Poly is so damed tough once that first coat soaks in. the second starts bui
lding. That's why when I do wipe, I flood the first coat with a brush, then
Splash some water on it, you will answer your own question. It is now plast
"Thinning", which he admitted to doing by approximately 50%, simply
means the layers of poly he applied were 50% thinner, meaning more
layers/coats are need to be applied to reach the same level of
protection as the unthinned product.
When contracting for a polyurethane hardwood floor finish I spec four
coats when "thinning" up to a maximum of 25%.
In his situation about the only benefit of thinning the poly is faster
Important to remember here is the method of application. I read this
over and over here and this is what I get from it. "I flooded the
surface and wiped off all the finish I could until it looked smooth."
Using jersey cloth you can <<easily>> get the finish left behind to 1
mil. of thickness. Using the average MSDS data, when the carriers and
solvents leave the unthinned product, the coating will shrink in
thickness about 66%.
So if one has thinned it further on their own, they will get 1/2 (from
thinning at the shop) the amount of 2/3rds thickness less (remaining
thickness after normal drying of unthinned product), or 1/6th the
amount of thickness recommended by the manufacturer.
You now have what is known as a "dust coat". Further application of
thinned product in the same manner will increase the thickness only
marginally, so one may now have as much as 1/3 the amount of finish
recommended by a manufacturer. But really, do you?
Probably not. The initial coating of finish will get more "traction"
and will more readily adhere to the surface. However, the second coat
will face a smoother, almost sealed surface and your application
method of applying thin coats with a rag can leave as little as .5 mil
coating behind. Figure in the shrinkage of the thickness after the
solvents and carriers are gone...
I would submit to you that it is not an apples to apple comparison.
In your situation, in my opinion, yours is exactly what is needed.
Their are two huge differences. First, your flooring guy doesn't put
down a few gallons of finish, then attempt to wipe off most of it.
Flooring urethanes are formulated different, and without thinning they
are almost impossible to get the correct layout of the product. They
are made to be thinned, probably to the 20% range. (NO ONE could
detect a 5% differential... probably not even a lab.)
Second, in an exactly controlled application as you speak, if you thin
all coats 25%, but put on 4 coats the manufacturers application
thickness requirement, you are exactly where you need to be when
Absolutely true. Thin coats of product do not provide adequate UV
protection (think down lights, tables by windows, etc.) nor do they
provide more than the smallest amount of abrasion resistance. These
are finishes for extremely light use such as in the homes of older
adults with no kids (and no drinking or eating buddies) and for pieces
to be admired. Easy to put on, nice to look at, but little utility
I have read that "wiping poly" is a popular and relatively foolproof
method of finishing. "Fool-proof" has an attractive sound to it for a
project with a lot of surface area to cover and me (yes, the "fool") in
charge of the application. I'm at least theoretically willing to
experiment with more sophisticated approaches, but not when I'm
finishing the better part of four sheets of plywood (plus the face frames).
My sense of it is (or at least *was*) that the thinned product, coupled
with the "wiping" application method, helps give a smooth even finish
without the need for much expertise. No brush marks, no puddles, no
bubbles. And in fact, I am quite pleased with the finish I got on the
bookcase boxes. It's smooth, even and doesn't look at all "plastic-y" or
thick. Could I really have gotten similar results with half as many
coats of the full-strength poly? I have done that in the past and have
not gotten as nice-looking a finish as I'm seeing now.
My take, too...it's not a for-sale piece where he's got to worry about a
customer down the road.
And, time will tell if there's a problem of insufficient thickness and
it'll be soon enough then to touch it up...
What could be more true?
If you are happy and the finish hits all your requirements, then you
are in the perfect spot. I have seen folks finish wood projects with
non boiled linseed oil mixed with some kind of solvent or more resins
and be thrilled. Looked great, and for the use of the piece, it was a
No doubt you can match the finish to the project without help. I hope
you didn't think I was lecturing; not my intent.
BUT.... (had to be one, right?) if you have a test piece of the same
wood with the same finish and amount of coats on it, then you can
easily test for final coat durability and appearance. You can add
another coat as needed, or if it fits the bill the way it is, you are
finished. (No pun intended...)
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