Is it a good idea to apply lacquer over shellac?

Question

I have an antique coffee table that I am planning to restore. It is elaborately carved, and appears to be made out of solid mahogany. The existing finish is in pretty good shape, except for the top of the table.

I believe that the finish is a colored shellac and someone must have spilled rubbing alcohol on the table and then tried to wipe it up which resulted in raised areas in the finish and a couple of spots where the finish has been completely removed.

My plan is to use denatured alcohol to refresh the surface, and level out the spots where the finish was smeared. I think I may be able to repair the areas where the finish has been removed.

Once the finish has been repaired, I plan to apply a few thin coats of spray lacquer to the top to protect the surface from future damage. Would a lacquer finish be the wrong approach?

Answer 1

Yes, shellac is a great barrier coat and wash coat, lacquer works well over it. The flake mixed with DNA is better than the hardware store canned. That being said, the area could be spot repaired with a fad via french polish and shellac without lacquer. I am assuming if it is has a shellac finish it is a vintage piece so keeping with the original finish is always a plus.

Answer 2

It certainly isn't a bad idea, depending on what you want.

You might want to consider refreshing rather than completely stripping and refinishing. Since shellac dissolves into previous coats you can often sand carefully (watch out for the risk of sanding thru a veneer!), restain if necessary and recoat.

(Actually, traditional lacquer is also often repairable, for the same reasons -- but that involves worse fumes and longer drying time than with shellac, so it actually isn't uncommon to use shellac to seal spot repairs made to lacquer finishes).

Answer 3

Would a lacquer finish be the wrong approach?

Your basic idea here is sound; on furniture such as a coffee table that will be in regular use shellac is not a good final protective coat because of its poor water-resistance and of course its solubility in alcohol.

However lacquer may not be the best bet here for a couple of reasons. The main one is that your lacquer's solvent may be 'hotter' than alcohol and if so the shellac will be soluble in it, which can lead to crazing after application. This is not a will happen, but some testing is advisable.

The other issue is brittleness. A quality polyurethane will add good water-resistance, improved resistance to scratching and slightly better resistance to knocks than lacquer because of its superior flexibility. So it is arguably a better choice for a day-to-day piece.

Also, in case it needs to be said: you should either mix your own shellac or buy a brand new can of premixed shellac. Shellac has a definite shelf life (despite manufacturer claims to the contrary!) once made up into liquid form; it is much better when used fresh, ideally within months of mixing.

Answer 4

On my can of Zinsser shellac "Not recommended for use as a sealer under polyurethane". It says nothing about lacquer. It sounds like some serious skill would be required to evenly match the original color.

I've been messing with using this stuff to finish the tweed covering on a reproduction Fender Tweed guitar amplifier cabinet. To add a little color I mixed about 3 parts clear shellac with one part amber shellac. The amber shellac alone was too dark and was difficult to get even coloring. I smoothed out a couple areas by wetting a paint brush with denatured alcohol, softening the finish and redistributing it.

You may be able to use aniline dyes to tint the shellac to match the original finish, but I'd be a bit afraid that the analine dye based finish may age differently than the original over time. .

Answer 5

I have found (dewaxed) shellac to be an amazing barrier coat. I haven't used it as a primary finish since I did decoupage as a kid, but I have sprayed dozens of gallons of dewaxed under both conversion varnish and poly as a barrier to who knows what kinds of muck is soaked into commercial (restaurant) bar tops. I prefer it over any of the sealers, vinyl or otherwise, that I have tried. Sprays nice with HVLP and dries at least as fast as lacquer.