Author Topic: Does Shellac Crack?  (Read 3348 times)

agaboric

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Does Shellac Crack?
« on: September 15, 2011, 01:56:35 PM »
I was wondering can shellac crack over time? My father found this nice looking hutch but the finish is cracking on it. He ask me about and I said it could be shellac, but I am not sure, how can you tell what type of finish is on an old piece of furniture?

Jeff L Headley

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Re: Does Shellac Crack?
« Reply #1 on: September 15, 2011, 09:46:27 PM »
What do you mean by cracking. It is probably a 50 to 100 year old vanish finish which cracks and crazes within that time frame. This is why I don't like most older and many newer varnish finishes. Easy to apply but hard to repair without abrasives. Would the finish be a dry desert cracking (large patches with large cracks in between or an alligator skin cracking (lots of small crazing with many small cracks) or just a lizard skin( bumps and rough with fine lines)cracking each mean different things? Please remember alcohol dissolves shellac and not a varnish finish. Be careful applying alcohol  to your surface if it is shellac. Try a hidden area first alcohol will remove a shellac finish quickly.
Please lay out whatever rags you use to dry individually. IF YOU WOULD BALL THEM UP THEY WILL SPONTANIOSULY COMBUST!!!

pearle

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Re: Does Shellac Crack?
« Reply #2 on: September 16, 2011, 12:05:45 PM »
Jeff Wrote "Please lay out whatever rags you use to dry individually. IF YOU WOULD BALL THEM UP THEY WILL SPONTANIOSULY COMBUST!!! "
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Is this correct? I know that oil finishes dry through an exothermic reaction that  may release enough heat to ignite rags, but I don't believe this is a hazard with shellac. The hazard with shellac (and with lacquer as well) are that the vehicle in which the shellac is dissolved (ethanol) is quite flammable. I can't find (after a quick Google-search) anything about the flammability of the shellac resin. I know lacquer resins can be quite flammable so we need to take cautions when spraying lacquers, but I don't know whether the same cautions are required for shellac. I think brushing or padding either is pretty safe.

I don't know a lot about wood finishes, but from my chemical engineering education I understand a little about chemical hazards. I think it's important to take appropriate precautions, but I don't think we should worry about things that aren't a hazard (i.e. shellac rags).

CBWW

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Re: Does Shellac Crack?
« Reply #3 on: September 16, 2011, 02:33:26 PM »
Shellac will not spontaniuosly combust but I take the approach in my shop that all rags are potentially combustable for those rare times that I actually use straight oil. 

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