shellac under varnish

[David Love]

I've always used shellac under varnish and never had a problem.  I like it
for a variety of reasons not the least of which it provides a nice surface
for rub-on soundboard decals.  I use flake dewaxed blond shellac and mix it
myself.  The canned stuff on the shelf is often pretty old by the time you
buy it and it only has a life of 3 years.  The main reason I brought it up
was that every time I open a can of varnish I can't help but see on the
label where it says "Do not use over shellac".  Well I've ignored it for
this long, but I thought I'd ask just in case there was something there.  

David Love
davidlovepianos@earthlink.net


----- Original Message ----- 
From: 
To: pianotech@ptg.org
Sent: 8/28/2003 9:27:10 PM 
Subject: Re: shellac under varnish


In a message dated 8/28/2003 2:00:10 PM Pacific Daylight Time,
bases-loaded@juno.com writes:


Subj: Re: shellac under varnish 
Date: 8/28/2003 2:00:10 PM Pacific Daylight Time
From: bases-loaded@juno.com
Reply-to: pianotech@ptg.org
To: pianotech@ptg.org
Sent from the Internet 
  David
   I have typically used shellac for a sealer coat on new boards on the top
and bottom before the ribs and bridges get glued on. I like the sealing
properties and it keeps  dirt, glue & water from glue cleanup from
impregnating the panel during ribbing. I always sand and then coat with
nitro cell. products. No problems here as to adhesions. I use one good wet
coat of the bullseye in a can, ooooohh I can hear the cringing from hear. I
spray it on. I quit using varnish over shellac after I lost several finish
jobs to the crinkles& varnish is tooo slow to cure for my schedule. What
can I say I'm varnish impaired. Love the smell though.


              Dale



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