Blotchy Shellac Finish

[EETStudent]

Just finished my first full, complete tweed cabinet(5E3 dimensions). Woodworking was done by a very skilled friend, and it turned out flawless. For my first time doing the covering, it turned out excellent and I know now how to do it better next time.

One thing I struggled with was the shellac finish. Turned out pretty nice, but its not perfect. The finish is darker in some places, lighter in others. Nice smooth finish looks like its been worn for several years. I took the following steps:

- 2 coats clear lacquer to seal the tweed. No sanding in between
- 3 coats 40/60 shellac, applied with nylon brush. Light sanding in between, heavier sanding after final coat to level the gloss
- 2 coats clear lacquer. Very fine sanding

The texture and glossiness is where I want it, but again the color is slightly inconsistent to my eye. Applying the shellac itself gave me some difficulties. It was difficult to spread evenly in some places and clotted up quickly. First coat seemed to go on fine, but subsequent coats intensified the coloring issues. Maybe I went too heavy on the coats.

Anyhow, any tips on applying shellac this way? Or suggestions as to what I can do to improve my technique?

[Jazz P Bass]

Give this a read.
Clear coat was applied first.
Link: ampage > Music Electronics > Guitar Amps > Design & Construction > 5E3 Builders : 1 : Need Clear Lacquer or Shellac Tips, anyone successful??
And this one.: http://www.thegearpage.net/board/arc.../t-381496.html

[Chuck H]

Was this an "amber" shellac or clear? Shellac is much too fast to apply the amber tinted product by hand without lap marks where the color doubles up. I'm a painter and "I" can barely do it.

[Kazooman]

Yep, shellac is difficult to apply well. It is an evaporative finish that does not change chemically as it dries, the solvent simply evaporates leaving the solids behind. The solvent in subsequent coats redissolves some of the first coat and repeated brushing around can create thick and thin areas giving the mottled blotchy appearance. This can be corrected by brushing the dark spots with straight denatured alcohol to dissolve some of the shellac. Unfortunately, the lacquer you applied over the shellac will prevent this. Some types of lacquer are also evaporative finishes and they can be removed with solvent. Others are reactive finishes that change chemically as they cure and they may not be as easy to remove. Either way, I would bet that any attempt to strip the lacquer and then the shellac from your cabinet would result in a big mess.

[EETStudent]

Good tip Chuck H. It was indeed amber shellac. Would there be an advantage to purchasing good spray equipment? I feel that my spray skills are solid, and Im sure I could get a good even application this way?

[Chuck H]

Since I paint houses (interior/exterior, free estimates, etc...) I don't actually have a sprayer that's good for shellac. So I use a Preval sprayer. It's a little bottle with an aerosol can that screws to the top. You can buy them at any hardware store. Thinning instructions are included with the unit but do experiment on something other than the actual work and make adjustments. If you plan to do a bunch of cabinets then any sprayer that's good for lacquer will work. BUT, even spraying you need to keep a wet edge at all times with a semi opaque product or the color will double up on overlaps. I've use amber on lye treated pine cabinets for an aged look (honey colored like old smokey bar paneling with blackened knots). I did four custom cabinets for this customer. The second coat is a clear sanding sealer, followed by sanding and two coats of polyurethane. Only the shellac is applied by hand. I don't think I would try it on a tweed cabinet though. Too much time lost waiting for proper absorbtion and brushing down bubbles. Time is the enemy in this process. On tweed I would go straight to polyurethane. Minwax makes a product called Polyshades that is a tinted polyurethane, with much longer "open time" than shellac, that has been successfully hand applied on tweed cabinets by many builders. follow with a coat of clear poly in whatever sheen you want.

I'm sorry that I don't know a way to correct your current project. If you absolutely can't stand it you could try removing some finish and color with lacquer thinner. If that doesn't work or gums up in the poors you'll be stuck recovering the cabinet.

[EETStudent]

Actually my current project turned out really nice. It came out looking slightly aged. It wasnt my intention, but it passes and for my first one, I feel tremendously proud and confident moving forward

My next questions was regarding the Polyshades Honey Pine. I have a quart of it, and I tried applying to a test piece of bare tweed. It didnt seem to spread well, but I could have been applying it incorrectly. Is a typical lint-free rag/cloth acceptable, and do you apply a sealer coat underneath?

[Chuck H]

Since I've never finished tweed (only read about it, But my finishing experience is extensive on other surfaces) I think your idea of applying a sealer coat is spot on. If you could somehow fill the poors of the tweed you could then apply a semi transpearent finish with a lot more control and less effect from absorbtion. In the commercial finishing world we call this a "french glaze". Not that it matters. But the point is that you already have a sealed surface and you can now control, by hand, the spread of color on the surface. Test samples, done with the consideration of the difficulties in finishing an entire cabinet, are your friend here. Good call.