Lacquer over dewaxed shellac

[Kyle Stiefel]

Hello,

Quick question which I think I know the answer but just want to verify.

There shouldn't be a problem placing lacquer over dewaxed shellac should there?

Thanks.

[Steve Schoene]

Remember that lacquer solvents will likely dissolve shellac. Brushing would not be a good idea, but it should be OK spraying, with some care to avoid a really wet first coat.

[Kyle Stiefel]

Remember that lacquer solvents will likely dissolve shellac. Brushing would not be a good idea, but it should be OK spraying, with some care to avoid a really wet first coat.

Steve,

You had commented on my other question about the purpleheart finishing. I was able to obtain some information and it looks like the way to maintain the color is to not apply any type of mineral spirits based finish.

Then the next problem was working the contrasting wood and not dispurse the purpleheart dust over the lighter wood. One solution is to seal the other wood (shellac, alcohol based). Then place lacquer over, however you wrote that brushing lacquer will probably dissolve the shellac, why?
Unfortunatley, I don't have a HVLP sprayer, it is on the wish list though.

The other method which would probably work would be to just use scrapers to create a far less dusty environment.

Heck, I am just thinking outside of my head here but further input on the lacquer dissolving the shellac would be great.

Thanks,
Kyle

[Steve Schoene]

Lacquer thinner sometimes includes methanol or other alcohols that can dissolve the shellac. Its a very varied product and not all lacquers are the same. I did a quick test and laquer thinner on shellac did soften it, but the thinner alone evaporated quickly enough that no real harm was done, but with the brushing lacquer it wouldn't evaporate so quickly. You could do your own test to see what happens--on scrap. Be sure to test a big enough surface so that the time factor spent brushing is similar to the project.

By the way, some lacquer thinners even include solvents such as toluene, xylene, and naptha, all components of mineral spirits, but all these solvents are not part of the finish once it has dried--they all evaporate away. Even in varnishes, the mineral spirits does not participate in the final finish, it merely thins the varnish to make it apply easily. The chemical reaction with the air that cures the varnish occurs after the mineral spirits have evaporated.

You can use the lacquer to seal the other wood before sanding the purpleheart just as well as using shellac. Just thin it to a workable consistence for that use.

But, I have seen so many different receipe's for keeping the color of purple heart that it is either easy to preserve the color--which I doubt, or impossible. For expamle, some swear that Armorall under lacquer is wonderful. After all, wood is a natural material and trying to preserve colors that nature intended to change is likely doomed to fail over time. In five years, I doubt any of the methods will have preserved the original color.