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TIP: Shellac for Holdout

bob coats finish finishing flexner lacquer shellac the finishing store varnish water-based woodfinishing woodworking

Shellac is often recommended as a sealer, with one of the justifications being that it provides “holdout” so fewer coats of finish then need to be applied to get the same overall thickness.

This is correct only if you are applying lacquer over the shellac, as shown in the first accompanying picture. I applied a coat of shellac to the right side of this panel and a coat of nitrocellulose lacquer to the left side. Then I applied a coat of lacquer to the entire panel.

There is a little better build on the right side with the shellac sealer coat.

But using shellac as a sealer coat doesn’t have the same effect with either water-based finish or varnish (including polyurethane varnish). In fact, the opposite is the case. For example, in the second picture, the right side with shellac applied under a coat of water-based finish shows less build than the left side with two coats of water-based finish.

The same is the case with varnish.

The explanation for the different results is that each coat of lacquer dissolves into previous coats of lacquer, which leaves the pores more open and the build appearing thinner. This doesn’t happen with water-based finish or with varnish. They don’t dissolve into themselves.

So applying any finish, including shellac, under lacquer, creates the appearance of greater build.

This is correct only if you are applying lacquer over the shellac, as shown in the first accompanying picture. I applied a coat of shellac to the right side of this panel and a coat of nitrocellulose lacquer to the left side. Then I applied a coat of lacquer to the entire panel.

There is a little better build on the right side with the shellac sealer coat.

But using shellac as a sealer coat doesn’t have the same effect with either water-based finish or varnish (including polyurethane varnish). In fact, the opposite is the case. For example, in the second picture, the right side with shellac applied under a coat of water-based finish shows less build than the left side with two coats of water-based finish.

The same is the case with varnish.

The explanation for the different results is that each coat of lacquer dissolves into previous coats of lacquer, which leaves the pores more open and the build appearing thinner. This doesn’t happen with water-based finish or with varnish. They don’t dissolve into themselves.

So applying any finish, including shellac, under lacquer, creates the appearance of greater build.



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