I am reading info on rubbing finish. There is one thing that I don't
quite understand. The instruction indicates that we should thin the
finish, let it hardened, and then rub the finish. This instruction may
be good for other finishes; but I am wondering whether this is
practical for poly. According to the instruction, the poly finish must
be thick; otherwise, when I rub the finish, I may run the risk of
rubbing through the top coat of the poly and revealing the line between
the top coat and the second last coat. But if I thin the poly for the
top coat, I will get a thin coat and I will have a high risk of rubbing
through the top coat. Something is missing here, right?

Is the idea of "thinning the last coat" more appropriate for other
finishes that one coat can melt with the next coat, and multiple coats
can become one thick layer?

Thanks for any info in advance.

Jay Chan

wrote in message
ps.com...
I am reading info on rubbing finish. There is one thing that I don't
quite understand. The instruction indicates that we should thin the
finish, let it hardened, and then rub the finish. This instruction may
be good for other finishes; but I am wondering whether this is
practical for poly. According to the instruction, the poly finish must
be thick; otherwise, when I rub the finish, I may run the risk of
rubbing through the top coat of the poly and revealing the line between
the top coat and the second last coat. But if I thin the poly for the
top coat, I will get a thin coat and I will have a high risk of rubbing
through the top coat. Something is missing here, right?

Is the idea of "thinning the last coat" more appropriate for other
finishes that one coat can melt with the next coat, and multiple coats
can become one thick layer?

Thinning the last coat is different that building up multiple layers for
rubbing out. thinning the last coat (or every coat for that matter) helps
the finish to smooth out and reduces the size of brush marks, thus making
the entire polishing procedure go faster and easier.

Manufacturers are making finishes thicker to comply with VOC regulations as
there is less oil or carrier to flash off to the atmosphere. By adding a
little thinner back in, you can get a better finish, even though more coats
may be needed.

Let that poly cure for two weeks before rubbing it out.

Polyurethane was never meant to be a fine furniture finish, subject to
the finishing techniques and applications that shellacs, lacquers and
other build finishes require.

As you know, poly is a film finish, and will stack onto itself, coat
upon coat. It will certainly adhere to the previous coat but it will
never become one monolithic layer.

The obvious advantage to a build finish is that you never burn through
a layer of finish, so you can "rub" or polish to your heart's content.
That is why it is used today and has been used for a few hundred years
as such.

But some here report great success with rubbing out the final coat of
their poly finishes. I have only hit a poly finish once with rouge (a
desk top) but never tried the full treatment of cutting down the
surface to a mirror reflection. Never had the confidence it would
work.

I would be interested to see what you try.

Robert

Edwin Pawlowski wrote:

Thinning the last coat is different that building up multiple layers for
rubbing out. thinning the last coat (or every coat for that matter) helps
the finish to smooth out and reduces the size of brush marks, thus making
the entire polishing procedure go faster and easier.

Manufacturers are making finishes thicker to comply with VOC regulations as
there is less oil or carrier to flash off to the atmosphere. By adding a
little thinner back in, you can get a better finish, even though more coats
may be needed.

Hi, Ed. I am just thinking out loud here... just speculating. I thin
my poly about 10% when I spray, and about 20% or so when I pad or foam
brush it on (depending on temp, etc.). I do that with every coat. I
learned the hard way that putting coat after coat on an uneven surface
will cause a lot of heartburn. Thinning does all the good stuff you
mentioned. But your post got me thinking...

Since the "rubbing out" of the last coat is the finish coat and you
need enough material to cut down the highspots (brush or lap marks),
wouldn't it make since to put on several thin coats all carefully
applied to maxiumum smoothness, and one last layer of pretty heavy to
that you would have plenty of film thickness to work with to level out
and polish? I have no experience in rubbing out poly, so as I said,
this is just wondering aloud. I would like to hear your thoughts,
though.

Let that poly cure for two weeks before rubbing it out.

AMEN! I was using Defthane for a while and their industrial coatings
rep told me that it was "green cured" at 13 days, and fully cured in
about 25 - 35, depending on the conditions of application. When I use
poly I don't even sand for final finish coat for at least 10 days or
so.

Robert

With the exception of one product that I know of, most poly is not meant to
be rubbed out. According to Jeff Jewitt, rubbing poly often produces a none
uniform sheen.
And yes, applying a thin coat of a layered product like poly before rubbing
out the finish does not make sense.

Cheers, JG
..
wrote in message
s.com...

Polyurethane was never meant to be a fine furniture finish, subject to
the finishing techniques and applications that shellacs, lacquers and
other build finishes require.

As you know, poly is a film finish, and will stack onto itself, coat
upon coat. It will certainly adhere to the previous coat but it will
never become one monolithic layer.

The obvious advantage to a build finish is that you never burn through
a layer of finish, so you can "rub" or polish to your heart's content.
That is why it is used today and has been used for a few hundred years
as such.

But some here report great success with rubbing out the final coat of
their poly finishes. I have only hit a poly finish once with rouge (a
desk top) but never tried the full treatment of cutting down the
surface to a mirror reflection. Never had the confidence it would
work.

I would be interested to see what you try.

Robert

wrote:

I am reading info on rubbing finish. There is one thing that I don't
quite understand. The instruction indicates that we should thin the
finish, let it hardened, and then rub the finish. This instruction may
be good for other finishes; but I am wondering whether this is
practical for poly.

Possibly yes, but with very particular meanings of "rub" and "thin".

In general, don't rub out polys. If you want to rub out a finish, use
one (like shellac) that merges well between layers, not one that leaves
distinct individual films.

If you do rub out poly, use pumice or rottenstone and nothing more. If
you rub out enough to penetrate through a film it will never look
right. Some people favour the plastic mesh abrasives instead, although
I've not used them myself. All I ever do is to use rottenstone (not
even 6/0 pumice) to slightly dull a poly finish and avoid the "plastic
kit" look. I do this with gel poly when I want the hard-wearing and
spillproof quality of a poly, but would rather it looked as if it were
oiled.

If I want something to look like french polish, then I french polish it.

wrote:
I am reading info on rubbing finish. There is one thing that I don't
quite understand. The instruction indicates that we should thin the
finish, let it hardened, and then rub the finish. This instruction may
be good for other finishes; but I am wondering whether this is
practical for poly. According to the instruction, the poly finish must
be thick; otherwise, when I rub the finish, I may run the risk of
rubbing through the top coat of the poly and revealing the line between
the top coat and the second last coat. But if I thin the poly for the
top coat, I will get a thin coat and I will have a high risk of rubbing
through the top coat. Something is missing here, right?

Is the idea of "thinning the last coat" more appropriate for other
finishes that one coat can melt with the next coat, and multiple coats
can become one thick layer?

Thanks for any info in advance.

Jay Chan

Thanks for all the helpful info that people have offerred here.

Seem like trying to rub-in poly is asking for troubles. Next time I
will use other finish that is more suitable for rubbing-in.

Jay Chan

wrote in message

Since the "rubbing out" of the last coat is the finish coat and you
need enough material to cut down the highspots (brush or lap marks),
wouldn't it make since to put on several thin coats all carefully
applied to maxiumum smoothness, and one last layer of pretty heavy to
that you would have plenty of film thickness to work with to level out
and polish? I have no experience in rubbing out poly, so as I said,
this is just wondering aloud. I would like to hear your thoughts,
though.

I have limited experience rubbing out poly, but you can get a truly
excellent finish if you take the time. I did one a few months ago and was
astounded by the results. Not plastic looking like poly usually is.

I think you are right, but we should clarify something.

Thick = large dimension
Thick = high viscosity

Thin = small dimension
Thin = watery

There is a difference between putting down a heavy coat versus putting down
a coat of thick (high viscosity?) material. The last coat should be flowed
on, not dragged out thin, for good results. Your 10% sounds about right.
So, a thick coat of thin poly sounds about right so it will smooth out for
easier sanding.

Make sense?
--
Ed
http://pages.cthome.net/edhome/

Edwin Pawlowski wrote:

SNIP

There is a difference between putting down a heavy coat versus putting down
a coat of thick (high viscosity?) material. The last coat should be flowed
on, not dragged out thin, for good results. Your 10% sounds about right.
So, a thick coat of thin poly sounds about right so it will smooth out for
easier sanding.

Make sense?
--
Ed
http://pages.cthome.net/edhome/

Yes, it does. I had to read it a couple of times, but I see what you
are saying and it makes sense. The flow out of the finsih on the piece
would be the key.

Although this thread is about poly, I think lacquer (although not as
sturdy a finish) would be much easier. For lacquer I build a coat as
recommended by my supplier to about 9 mil (I know... I thought he was
kidding the first time) and then plan on cutting it back to abou 6 mil
when finished. I sounds like a lot, but the three mil I take off is
only equal to the thickness of a dollar bill. It requires smooth
application on all coats to get to 9 mil.

Do you know how much material (thickness) you are cutting off when
polish out the poly? Do you remember what brand you used and how many
coats you applied before rubbing out? One last one, what did you use
to rub out the finish - hand powered or machine powered, and what
grit/polish did you use?

I appreciate the response. I would love to set up an experiment to try
this and have a left over quart of poly to try it with. This is how I
learn. It would kill my associates/competitors to find out I had
rubbed out a poly finish, even if it didn't look french polished.

Thanks -

Robert