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shellac surprise

Kevin Jenness

Kevin Jenness

Joined
Nov 15, 2020
Messages
814
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Location
Huntington, VT
Putting a sealer coat on a couple of open mouth vessels I thought I would speed things up by pouring some shellac into the interior and rolling it around. Big mistake. The shellac swelled and bubbled the endgrain bottoms, particularly around a knot, to the extent that the pieces were raised up off their bases. It was as if the shellac were water. The swelling dissipated overnight, though not completely. From now on I will pad on shellac, use my hard oil topcoat or leave the insides unfinished.
 
I’ve had cracks show up doing it. Most of my finishing uses wipe on poly, and I use it vs shellac. The poly has never caused the same issue.
 
Did you mix the shellac yourself using DNA? I know that DNA, at least the Kleanstrip stuff sold around here, has water in it. I've always been wary as a result. I sometimes get a bit of grain raising with some woods when sealing with shellac.
 
Jon Rista said:
Did you mix the shellac yourself using DNA? I know that DNA, at least the Kleanstrip stuff sold around here, has water in it. I've always been wary as a result. I sometimes get a bit of grain raising with some woods when sealing with shellac.
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I used 99% isopropyl alcohol, mixed recently. I know that alcohol, being hydrophilic, is used to speed drying in green woodturning blanks by replacing cellular bound water and then evaporating more rapidly than the water. I didn't consider that alcohol would be absorbed into dry wood with great rapidity and swell the material as water does. Perhaps a chemist here can elucidate.
 
Jon Rista said:
Did you mix the shellac yourself using DNA? I know that DNA, at least the Kleanstrip stuff sold around here, has water in it. I've always been wary as a result. I sometimes get a bit of grain raising with some woods when sealing with shellac.
Click to expand...
Alcohol will raise the grain. Not because of the water in it. Just because it will. I often do this with 99% isopropyl before my final sanding grit.
 
Brian Nowak-Thompson said:
I’m a chemist and the simplest way to explain the issue is that alcohols have an -OH group just like water. Therefore they interact with wood similarly to water. Just not quite as much due to the other atoms present in the molecule.
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Thanks for that. I've been using 99% isopropyl to wipe off sanding dust prior to finishing. I haven't noticed grain raising, but haven't looked for it, either.

I used to use MS, but that seems to leave a "residue". But since my finishing products generally contain MS, maybe that doesn't matter, and MS is the best choice?

I'm not fond of using acetone as it penetrates nitrile gloves.
 
last week I had the same thing happen. Had a few punky spots, so I saturated with shellac sanding sealer. Crack opened up to 1/2” wide. Closed up to this after it dried. IMG_0461.jpeg
 
Mark Jundanian said:
Thanks for that. I've been using 99% isopropyl to wipe off sanding dust prior to finishing. I haven't noticed grain raising, but haven't looked for it, either.

I used to use MS, but that seems to leave a "residue". But since my finishing products generally contain MS, maybe that doesn't matter, and MS is the best choice?

I'm not fond of using acetone as it penetrates nitrile gloves.
Click to expand...
Alcohols come in a variety of structures (and flavors!). Methanol is the simplest with one CH3- group, ethanol is next with a CH3CH2- group, etc. The more carbons in the group, the less like water it is. You would find that the alcohol after isopropanol (butanol) would be only partially soluble in water. So I would expect isopropanol to raise the grain less than ethanol. But most alcohols we have available are mixed with other things (like water).
 
I use shellac quite a bit as a finish and sealer. Mix it myself from flakes and yes, I've had it "swell" the bottom end grain of a piece to the point where it no longer sits flat the next day or so. Also prompted me to put just a bit more concave curve in the bottom of my pieces since it might happen in a high humidity environment some day as well. I don't saturate with it but I may brush it on the inside of a hollow form to seal and enhance the color but still, brushing it on but not soaking it.
 
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