Sanding sealer is a compound that contains metallic soaps (sterates) that
keep sand paper from clogging. These can also cause adhesion problems with
finishes. They aren't something you want to use.
What should have been recommended is a pore/wood filler. These are used on
open pored woods such as oak and walnut to fill the open pores to a point
were they are level to the surrounding wood surface. Not using one on an
open pored wood when finishing with a surface finish (shellac, lacquer, or,
varnish) will give the finish cratered surface. Pore fillers can be
commercial fillers, the finish you are using applied and sanded back till
the pores are filled, or shellac applied and sanded back till the pores are
Yes. polyurethane is a varnish. A varnish is a mixture of a thinner (usually
mineral spirits), a carrier (tung oil or some other kind of reconstituted
vegetable oil) and resins (used to be things like rosin and amber, now
mostly man made).
Three basic type of varnishes you will find at you neighborhood supply store
will be Spar/marine varnish, varnish, and polyurethane (also in a spar
Spar varnish is a long oil varnish (a higher ration of oil to resins)
formulated to be more flexible then standard varnish to accommodate the more
radical movment of wood exposed to the whims of the weather. Just plain
varnish has a smaller oil to resin ratio and is more brittle then spar
varnish. Polyurethane is the same recipe as just plain varnish but the
resins used are more chemical and scratch resistant (which is why people who
rub out finishes tend to avoid it) resins then that found in just plain
Application of all three is exactly the same process. If you have to rub out
a varnish finish just plain varnish is the one to choose since it's cured
properties lend itself better to the process.
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