Painting over shellac

A friend of mine was asking me about a piece of furniture that she wants to paint. It was purchased unfinished and she had someone put on shellac many years ago. Now she wants to paint it. Not surprisingly, she didn't know if they used dewaxed shellac. So some questions:

--does the shellac have to be dewaxed to paint over it (she didn't say what kind of paint)?

--is there a way of determining if a shellac finish has wax in it?

--can you put dewaxed shellac over a wax-containing shellac finish, or will the dewaxed shellac that's applied dissolve the finish below and still create a waxed shellac finish, though perhaps with less wax?

--what will work here, short of stripping the shellac finish?

Rob

Cannot answer all of your questions BUT the good news about shellac underneath is: It can be removed easily in 15 minutes or less. (thats why its not reco'd as a bartop etc as its not alcohol resistant like poly or varnish) Simply moisten a rag w denatured alcohol and the shellac will quickly dissolve and therefore be removed so you can start from scratch. I would then finish off w laquer thinner before starting the new process. I believe its safe to paint over either waxed or dewaxd shellac but let the experts respond on that portion.

>> does the shellac have to be dewaxed to paint over it (she didn't say what kind of paint)?

No, if oil based paint is used. Yes, if waterborne paint is used.

>> is there a way of determining if a shellac finish has wax in it?

Not practically.

>> can you put dewaxed shellac over a wax-containing shellac finish,

Yes, that will work.

As said, stripping a shellac finish is relatively easy. It is readily dissolved by denatured alcohol.

Let me say that no matter what she does, she will have to clean the surface well. Mineral spirits will do this. Wipe it on and then wipe it off using lots of fresh paper towels and keeping a fresh face on the towels. I generally then scuff sand with 220, dust and then wipe again with mineral spirits.

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Originally Posted by Howard Acheson

Let me say that no matter what she does, she will have to clean the surface well. Mineral spirits will do this. Wipe it on and then wipe it off using lots of fresh paper towels and keeping a fresh face on the towels. I generally then scuff sand with 220, dust and then wipe again with mineral spirits.

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Thanks guys, very helpful. Howie, what is the function of the mineral spirits--is that something you do b/o of the shellac, or do you also do that when you prep plain wood for finishing.

>> what is the function of the mineral spirits

Mineral spirits is an excellent degreaser/dewaxer. It will remove accumulated wax, furniture polish and other gunk that can contaminate the surface preventing good adhesion of another finish.

Quote:

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Originally Posted by Howard Acheson

>> what is the function of the mineral spirits

The mineral spirits used for a laxitive is fairly thick. The mineral spirits thins it a little. For that matter you can used mineral spirits as your lubricant. Water with a drop of dishwashing liquid works well for all but shellac and waterborne.

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Howie,
I'm afraid you've totally lost me here in your reference to laxatives and lubricants. I thought you were talking about wiping the surface down and I was just wondering about why you need to use mineral spirits for that.
-Rob

Um, Howie..."Mineral Oil" (laxative/cutting board finish) is a little different than "Mineral Spirits" (solvent/paint thinner).... ;)

Rob, wiping the surface with mineral spirits is a nice way to clean a workpiece off before a finishing step or even between sanding grits. MS also dissolves wax. I also use it as a "wet sanding lubricant" when smoothing a clear finish between coats.

>> I'm afraid you've totally lost me here in your reference to laxatives and lubricants

Opps, guess I got into the martinis too early yesterday. I was thinking about a response I made on another forum just before.

I have editted my response to something that makes more sense although Jim covered up well for me. Thanks Jim.

So mineral spirits will not eat the shellac like alcohol will?

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Originally Posted by Ross Lowry

So mineral spirits will not eat the shellac like alcohol will?

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No, mineral spirits will not harm any of the standard finishes once they are fully dry. It's not a solvent to any cured finish.

Has anyone actually tried non-dewaxed (i.e. waxed, natural) shellac? I've read online in various places how some painters/finishers think it doesn't matter if the shellac has it's natural wax in it or not. It almost seems to me that such a rumor was started and now everyone repeats it because it sounds very reasonable and plausible. Perhaps it isn't really "wax" as we understand it that most feel is necessary to remove from shellac. I dunno...just some food for thought and wondering what others know about this. Was shellac dewaxed 50-100 years ago?

To that end, I have a front door finished with I-have-no-idea-what so I planned to shellac it (Zissner), paint it, and reshellac it.

The reason IMHO there is concern over wax vs dewax in shellac usually refers to applications of varnish (esp Poly) when coated over shellac. The poly varnish will adhere much better if shellac is dewaxed. It is usually not reco'd to apply a poly varnish over a standard (not dewaxed) shellac. If you are painting over it, not an issue..HTH. BTW I use dewaxed in all my furniture projects as insurance.

If it were me, I'd scuff-sand it with 150-grit or so (to clean it, and give "tooth" to the primer/paint), tack off the dust, then prime it with white-pigmented shellac (Zinsser's BIN or similar), then paint with whatever floats your boat.