Shellac coming off

Seems strange to me, though I am hardly an expert. I only have two thoughts. First, if the shellac were bad, it would not dry very well. If it dries well, I assume it is ok. Second, when I use shellac or any other clear finish over wood, I never sand the wood to 400 grit. In fact, I don’t go beyond 150 or 180. I am pretty sure I got that from Paul. I do not know whether that would make a difference, but it might be that the shellac needs something to grab hold of. After Paul is finished with his plane, he often lightly scuffs the wood to give it (I think the word is) tooth before putting on shellac or other varnish. So maybe that is the problem. Oh, I often do use some 400 grit (very lightly) after my first coat of shellac or other varnish to smooth it out.

I agree with Sanford as far as sanding. Based on Paul’s instruction (and my own experience following his example) I don’t sand past 240/250, and even then just very lightly, and really I only sand to give the wood some “tooth” so the shellac has something to hold onto. I feel like sanding to 400 prior to shellac wouldn’t give that amount of tooth. I also wonder if you’re applying too thick? You said you apply 3 layers then wait overnight and apply 3 more layers, so are you not allowing it to dry between those layers? Shellac is not like polyurethane … the layers do not build upon each other, instead each coat will dissolve the previous coat and combine with it. If you are applying “3 layers” at once, it will be very thick and won’t be able to dry properly. The result should almost seem like part of the wood, rather than a coating over it.

I see, I misunderstood what you meant about the layers (I think “coat” is the word you’re looking for). I do think 6 coats is quite a lot, although I suppose it depends on the intended use, but I’m pretty sure I’ve never applied more than 4 coats, and usually I only apply 3 coats. I also use the Bullseye (Zinsser) shellac, straight out of the can, applying somewhat sparingly with a hake brush. The couple times that I’ve had a large surface to finish, I did cut it 1:3 with denatured alcohol (ethanol) — 1 part alcohol to 3 parts shellac — just because that made it easier to apply over the large area. If it’s an average-sized coffee table I’d probably cut it to prevent the brsuh from sticking as you go, but that’s not much of an issue for something smaller like an end table.

So my general procedure is:
– lightly sand with 240 grit
– apply the “sanding coat” of shellac (this first coat is absorbed rather quickly, so I’m not too concerned with how thick it is)
– let it dry maybe 30 minutes
– lightly sand with the same (now used) 240 grit
– apply another THIN coat of shellac and let it dry several hours
– then I make a judgement call whether to sand again or proceed directly to the 3rd coat. If my 2nd coat was blotchy/globby I’ll clean up the bad areas with a chisel and/or sand again with 240.
– apply the 3rd coat and let it dry overnight.
– at this point it’s another judgement call between smoothing globs with 240 and/or using 0000 steel wool
– once the surfaces are completely smooth, apply wax with 0000 steel wool
– let the wax set for about an hour, then buff with a cloth or shoe shine brush

I can’t say for sure why your finish is coming off, but my suspicion is that sanding to 400 did not allow the first coats of shellac to penetrate the wood, and therefore subsequent coats were not adhering completely, so those 5th and 6th coats are just hanging out waiting for a coffee cup to come along.