How thin do you go with shellac?

[Taylor Ham]

I understand that one of the chief virtues of a shellac finish is that it can be left very thin, and durability is inversely proportional to that.

I am currently level with the masking tape over the bridge footprint, a tiny smidge less than .002.

Any issues if I stop soon?

[charles Tauber]

I can't speak for anyone else, but I don't approach it that way. Instead, I put on enough shellac - with a pad - that I have a smooth film and, for open-pored woods, the pores are filled. That takes a while, lots of coats.

When I have achieved that, I'm done, but for any spiriting/buffing out. The result is a pretty thin finish, since it is difficult to get a lot of build/thickness unless one is at it for a long time.

I haven't measured the finished film thickness, but it isn't anywhere near the thickness of standard masking tape: I also use masking tape on bridge and fingerboard areas.

[Taylor Ham]

The pores are just about filled, and the surface is pretty smooth. So it sounds like I am good to stop.

I am padding on Royal Lac. The masking tape I'm using is way thinner than typical tape, intended for fragile surfaces. The adhesive is also weaker as a result, which should help avoid tearing out slivers of spruce.

Interesting side note, Taylor makes a point of the thin finish on their 600 series and up: 4-4.5 mils. At roughly a third of that I'd say french polish / padding is the way to go for thinness.

[nikpearson]

...but as you say a typical French polished shellac finish will be considerably thinner again. Much more fragile as well, particularly during the first few months when the shellac is still relatively soft.

Still my favourite finish and it’s easy to repair if you know how to.

[Quickstep192]

If you've had the same tape masking the bridge area since you began shellacing, be careful removing the tape so you don't pull up the shellac or wood fibers from the top. A careful score with a razor blade will help avoid pulling up the shellac. Warming the tape with a hair dryer (not heat gun) will help prevent the tape from pulling up wood fibers.

[Taylor Ham]

Originally Posted by Quickstep192

If you've had the same tape masking the bridge area since you began shellacing, be careful removing the tape so you don't pull up the shellac or wood fibers from the top. A careful score with a razor blade will help avoid pulling up the shellac. Warming the tape with a hair dryer (not heat gun) will help prevent the tape from pulling up wood fibers.

Thanks for the tips. I've been going back over the bridge mask with pure alc after every three coats, so there's no shellac on top. I used this as a guage for the finish thickness- when it's even it must be around 1.5 mils. should help with peeling too.

[Simon Fay]

I always ended up around 2mils or so with French Polish. You can go a bit thinner than that but I wouldn't advise it. FP is delicate and gets removed over time in certain locations -- so it helps to have just a little bit of a buffer against that happening right away.

[redir]

How do you even measure something so thin?

I stop polishing when it just seems like it's right. For me that's usually about 20 sessions after every thing is pore filled and sealed. After about ten sessions I will level with oil and sand paper. Then do another 7-10 sessions, level again then glaze the finish. I don't use abrasives on shellac to polish it out.

[Victory Pete]

There are meters made for measuring finish thickness, they are expensive. I used to French Polish but now spray shellac. I estimate how thick my finishes are by putting a small aluminum flashlight on the top and you can see a circular line in the finish that shows the apparent thickness.

[Simon Fay]

The meters apparently don't work well for wood - at least, not reliably so. There are two ways we measure finish thickness.

One is to use Frisket tape to tape off your bridge and fretboard. If your finish is level with the tape, then you have a pretty decent estimation as to the thickness of the finish.

The second is how I ultimately determine thickness and that is during the removal of finish from the fretboard and bridge areas. I score these areas with a single edge razor blade and use a chisel to remove the finish from the wood in preparation for the joining of the bridge and neck. I simply measure the film thickness from the shards of finish that are removed.

Aside from using either of those methods, you are pretty much just guessing. Additionally, those measurements don't guarantee that you applied the finish in an even manner.

[rccosta]

One of the big benefits of shellac is you can easily go back and re-apply if you ever go too thin. No harm in too thin, then, as long as you carefully monitor your guitar for thinning regions (typically around the arm-rest, plectrum-stroke region, and frequent case-contact areas).