I am curious as to why and if this is a common occurrence. After applying several layers of dewaxed shellac on a piece of walnut once it dries it appears as if the pores in the wood are gassing and causing bumps fo shellac to appear over the pores of the wood. Am I doing something wrong or is this normal?
Thanks,
Bill
Replies
I use a fair amount of shellac; not a ton but, I do buy it in gallons. Zinsser Seal Coat dewaxed shellac gets hit 50/50 with DNA for my first coat. I'm sure you've read people say "thin, thin coats" when referring to shellac. I have gotten nibs from tiny particles in the air settling onto the surface. These literally wipe away with some 1200 or 1500 grit paper of pads.
I'm no finishing guru but, I have been padding, spraying and brushing shellac for nearly 20 years. What is the cut of your first coat and how are you applying it please?
Often outgassing is a result of the wood being warmed during or after the application of a sealant such as epoxy or polyurethane. Is there a possibility you are warming up your shop prior to applying the shellac and the wood is still warming up during or after application? A common mistake people make is to apply finish then warm the project to cure the finish either with a heater or a lamp.
I know that for epoxy the ultimate situation is to warm the shop area, and the wood, turn off the heat, coat the project, then cool the shop so the wood inhales the epoxy.
I don't know if your observation is the same as this one, but I too have noticed that in brushing shellac, the finish gets "bumpy". By this I mean that around the pore of the wood a ring of shellac forms that is higher than the rest. This is from the surface tension of the alcohol causing the finish to crater around the pore. It is the nature of the beast. The typical way to address this is to get enough material on to sand down later with wet 400 gt. paper and then pad on shellac. Padding usually dries so fast that the finish doesn't have a chance to move and crater. Or you could learn to French polish. I have not seen outgassing in shellac. I have seen shellac raise the grain. Again, sand it down and apply shellac.
Thanks for all the responses.
First I apply really thin coats many times, 5 or 6, so I think I am OK in this regard.
As to warmed wood? this is a possibility, but if it is the cause it might be afternoon sum hitting the piece. I'll see if this is happening?
Third, I too use 400 grit to sand between coats and apply very a thin coat.
It usually takes over night drying for the problem to show in a new coat and when I checked this morning, I seemed to have resolved the issue. It may show up later today. I will have to wait and see. I used air yesterday to thoroughly blow out any residual dust in the pores from sanding, applied a coat. then let the piece dry vertically instead of horizontally. So far so good. Thanks again for your helpful suggestions.
Bill
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