Sanded through shellac, now new coats won’t stay on bare spot
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I set out to build up about 5 coats of shellac on the ebony headstock on my banjo project. I wanted it dead flat (level) so I could polish it out to look perfect. The whole thing is only about 3″ wide by 5″ long. Using Zinsser 2lb sanding sealer, I put on a light coat and then sanded off any raised grain. I then proceeded with subsequent coats sanding only every two coats. I noticed that the finish was getting a bit uneven and in my effort to sand it level, I sanded through the finish in one spot, at the edge. Now, the next coats I’ve applied don’t seem to be building on that area. The effect looks much like witness lines when you oversand varnish. Any advice?
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Shellac sand through
In my experience, it is one of two things. Your sandpaper is high in sterates, (lower priced offshore stuff) or the ebony is too smooth to take shellac. All is not lost, here are some options.
Use a pad with alcohol only. This will clean out the bare area, and help to smooth things out. Sand with 400 wet/dry using a combination of mineral oil and mineral spirits as a lubricant, ratio is right when the mixture flows well. Wipe with naptha and check adhesion again. Check the date on the can, the shelf life of that product is only a couple years. Cut the shellac with half shellac thinner, use fresh alcohol, as it sits, the thinner absorbs moisture. This 1 pound cut "spit coat" will absorb better and help to bridge the surface for application of some 2lb for the finish. When in doubt, pad with alcohol only. Damp not wet.
This is a lot to digest and seems random, it is not unusal to have these problems with French polish on ebony. One or a combination of these fixes will get this back on track.
Does the shellac appear to be pulling away from these areas, as if you have fish eyes, or is it just that the shellac just appears to be soaking into these areas and not building on the surface?
"or is it just that the
"or is it just that the shellac just appears to be soaking into these areas " At first it appeared to be pulling away, but not the way a fisheye does. Now I wonder if it was just soaking in. I wiped it down with alcohol as renthal suggested and shot two additional coats. Things are looking much better. I think I'll build a few more coats before sanding again.
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