Shellac disaster

[Ron Coleman]

Yesterday I finished truning a small spalted maple piece and decided to give it a quick sealer coat of shellac before the final finish of lacquer. I quickly brushed on several coats of very dilute shellac (maybe1/2 pound cut) and the wood soaked it up like a sponge. I set the piece on the bench to dry and about 10 minutes later I checked it. I picked the piece up and then noticed a GIANT CRACK (3/16" wide) running up one side, across the top, and down the other side. :eek: I also coated the lid for this piece with shellac and it curled up like a potato chip.

NUTZ, just spent about 4 hours on this thing and I get a big crack.:mad: After I calmed down, I got to thinking the alcohol in the shellac must be acting just like water causing the wood to expand.

After watching the crack for several hours I noticed it was starting to close. About 5 hours later it was completely closed and I soaked a little CA into it and did a little fine sanding. Today I gave it several coats of lacquer and the crack is gone. The lid is nice and flat too.

Anyone else ever have this problem with shellac?

Ron

[Ron Sardo]

It's not the shellac that caused the cracking.

But you are on to something about "acting like water". Your typical can of DNA, when freshly off the shelf, may contain somewhere from 10%-20% water.

Diluting the shellac to a 1/2 cut really "may" be the problem. Because it introduced allot of water into the wood.

As to the crack closing, that happen to me once about 3 years ago with some spalted apple. The crack is still closed today and I didn't use any CA. Weird Huh!

[Dennis Peacock]

Ron,

You might try a 50/50 mix of lacquer thinner and lacquer for the seal coat. Many coatings can be used for a "seal coat" when thinned 50/50 or more. It's very possible that the alcohol wet the wood, cause the deformation and then dried back out and closed up the crack and the lid flattened out. At least with the thinner/lacquer mix, you don't have to worry about added "wet" to the wood. Glad it all turned out ok for you though.

[George Tokarev]

Alcohol is 100% mixable (miscible) with water. Doesn't act on wood like water when the water's there, because the more polar compound does the hydrogen bonding to the cellulose, though the volume of free liquid is increased briefly. Your shellacing didn't have anything to do with what you saw. The superficial wicking into the lignin-deprived white areas was the most evident, but there was also a lot of air space to run into, and alcohol has a lower boiling point, so evaporates quickly, even when it tries to hide.

The piece was still adjusting stress and moisture content. From what you described, opening and closing, you have a piece that was taken from a fairly high relative humidity, or at least had high moisture content, and brought in to a dry place, probably had some heating from the turning process, and might even have been near a heat register in that ten minutes of neglect. The moisture couldn't get out of the interior fast enough to replace the loss from the surface, so the shrinkage opened a crack. As the moisture equalized inside the piece, the crack closed.

The crack's still there, you know. A lot of people don't realize that the wood they are turning contains cracks from the time it spent drying before they turned it. Why it's really a good idea to do a reveal with liquid after the initial trim. It'll wick into an old closed crack, revealing it for you to cut away or try to maintain with CA.

[Ron Coleman]

It's not the shellac that caused the cracking.

But you are on to something about "acting like water". Your typical can of DNA, when freshly off the shelf, may contain somewhere from 10%-20% water.

Diluting the shellac to a 1/2 cut really "may" be the problem. Because it introduced allot of water into the wood.

As to the crack closing, that happen to me once about 3 years ago with some spalted apple. The crack is still closed today and I didn't use any CA. Weird Huh!
Well I did a little test this morning just to see what was causing the problem. In the picture is an edge view of a piece of 1/4" walnut that was dead flat and has been for many months. I brushed one side of the walnut with several coats of alcohol only from the same can I used to mix my shellac. The picture was taken about 15 minutes later. On the right is the spalted piece that cracked and the cracked area is visible. To the left of the square in the background is another piece that warped too.

I'll keep an eye on this piece and see how long it takes to get back to flat.

Think I'll stick with my favorite lacquer technique.

Thanks for the info about the alcohol and water.

Ron
http://mrcol.freeyellow.com/turning-stuff/4361.jpg

[George Tokarev]

LOT of water in that. Does the shellac made with it even cure?

[Ron Coleman]

LOT of water in that. Does the shellac made with it even cure?

I haven't had any drying problems with the shellac. Think I'll head to the liquor store and get some real alcohol for the next batch. :D

[Charles McKinley]

Hi Ron,

At least you can still get Ever Clear in Ohio. The Communism of Pennsylvania has banned it! I gues there were too many batches of gabargae can punch being made.

[Ron Sardo]

I haven't had any drying problems with the shellac. Think I'll head to the liquor store and get some real alcohol for the next batch. :D

Do you anybody who makes moonshine? Same stuff with the Denatured stuff addeed.:rolleyes:

[Ron Coleman]

Do you anybody who makes moonshine? Same stuff with the Denatured stuff addeed.:rolleyes:

Think I might have to make a trip to southern Ohio and scout out a new source for shellac fixins.