shellac under varnish

[gordon stelter]

I have read that shellac under varnish is the prime
culprit in "alligatoring", as shellac dries by
evaporation, while varnish dries both by evaporation
and oxidation. So shellac continues to shrink until it
is very brittle. And varnish expands.
     Thump

--- bases-loaded@juno.com wrote:
> Hi David -
> 
> Shellac is actually an excellent choice for a sealer
> coat under
> "traditional" varnishes, but under the more modern
> Polyurethane
> varnishes, which seem to comprise the majority of
> the product lines these
> days, only dewaxed shellac will allow for proper
> adhesion between the
> shellac and poly.  Polyurethane is very persnickety
> about what it adheres
> to, to the point where it really doesn't even adhere
> to itself that well
> unless proper techniques are employed.  And
> certainly, the natural wax
> content found in conventional shellac products would
> prevent the poly
> from achieving good adhesion.  That's my take on it,
> anyway....  With
> dewaxed shellac, you are safe with any finish I can
> think of.
> 
> Mark Potter
> bases-loaded@juno.com
> 
> On Thu, 28 Aug 2003 08:36:38 -0700 "David Love"
> <davidlovepianos@earthlink.net> writes:
> > Why is it that many varnish manufacturers advise
> not to use their 
> > products
> > over shellac.  It is my understanding that shellac
> was traditionally 
> > used
> > as primer coat for varnishes?
> > 
> > 
> > David Love
> > davidlovepianos@earthlink.net
> > 
> > 
> > 
> > _______________________________________________
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> > 
> > 
> _______________________________________________
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