I use a fair amount of wiping poly finish and have used pre-mixed and my own 50/50 (poly/spirits) brew.
I have a small project in the garage and decided to use the remainder of a can of Minwax Wipe-on satin. First two coats are on but I am probably going to run short. Does anyone see a problem with putting home brew (above) on top of the factory mixed? I have a can of Minwax Satin and spirits. My main concern is making sure the dulling agent in the canned finish works on top of the premixed finish.
Just trying to keep from making a 40 mile round trip to buy another can of wipe on (we are rural).
Adding thinner won't change the sheen. The dulling agent works because it
makes tiny little bumps that reflect the light differently...same effect as
sanding with very fine sand paper.
As long as the Minwax is an oil base finish, the only thing that your home
mix will do is thin it. Even that isn't likely as that is what wiping
varnish is...thinned down regular.
Well, the end effect is similar but that isn't the mechanism by which
flatting additives work--they do cause light reflection to be different
but not by causing surface roughness by by having refractive surfaces on
the particles themselves...
Here's one article; I can't seem to find my link to Chris Minck's tome
offhand that's "everything a professional finishes chemist knows about
finish chemistry for the woodworker"...
If thin _too_ much it undoubtedly will have some effect on the sheen
altho probably won't be much noticeable since apparently has already got
at least a couple coats of the original product on that will still serve
their duty underneath even if the top coat or two aren't as flat as
would otherwise be owing to dilution of the amount of agent...
The biggest effect will be simply that the final finish after the
thinner has evaporated will be however much thinner than otherwise would
have been based on the amount ratios of thinner:product used.
Which would mean they are exposed. Which means they roughen the surface.
The flatting powders with which I am familiar are talc and fumed silica.
The roughness created depends on how much of which. I used to make my own
mix for flatting lacquer using talc; I wanted a surface rough enough that it
would pick up pencil marks (I was retouching photographic prints). Add
enough talc and you get a *very* rough surface...maybe around #360 silicon
carbide or coarser. It isn't a hard surface, of course, and will scratch
Also, I know that most flatting agents are sold in a paste form. Doesn't
change the fact that they are generally talc and/or fumed silica
("Cab-o-Sil") that have been mixed with whatever to make a paste. Used to
be one could go to a paint store and buy flatting powder by the ounce or
pound. No idea why that is no longer true but would guess that they can
sell it for much more as a paste. Obfuscation, IOW.
No, they're not exposed; they refract light and don't reflect directly
As the reference points out, the point of adding the flatting agent is
to provide the equivalent sheen _w/o_ having to rubout/roughen the surface.
You are a rascal and a daredevil, Ron. Asking total strangers about
the end result of finishing your woodworking project, is well....
First, your home brew and their wipe on are two different materials.
Yup, both solvent/resin based, but the wipe on from the store has a
slightly different resin (according to my Sherwin Williams industrial
rep) than their regular canned brush/spray applied product. More
importantly, the wipe on has a plasticizing agent in it to improve the
end result of wiping. It extends your open time on the surface as
well as improves the ability of the applicator to rub it down to a
The two products in question aren't that dissimilar, but poly finishes
can be very unforgiving. The last thing I would want to see is
witness lines, tiny bubbles, or anything else that could be caused by
dissimilar solvents (thinner, mineral spirits, etc.) outgassing at a
different rate than another finish.
Since I do this for a living and have to guarantee my work, I wouldn't
think once about getting in the truck with a mug of coffee and getting
more of the exact finish needed. Done it many times, cursing the
whole way, but I never apply dissimilar finishes.
Weigh the downside. Surely your project is worth another 40 minutes
of your time (that isn't even across town for me... rural or not) to
make sure your work is going to wind up well. How long would it take
to strip an refinish your project if it goes wrong? Wouldn't you want
the confidence to know you did it right? If you didn't have your
doubts, you wouldn't have asked...
On Saturday, February 2, 2013 10:01:06 AM UTC-6, RonB wrote:
Thanks guys - As it turned out I was pessimistic. I got four coats on the medicine cabinet project and had finish to spare.
BTW - Speaking of home brew, we are heading into year two on a blend I brewed for some redwood Adirondack chairs. Equal parts BLO/Spar Varnish/Mineral Spirits. It is probably too early to declare victory but the color and surface is holding well. There is some dulling in the top of the right arm where my coffee cup or beer glass goes but overall they look great.
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