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shellac surprise

Kevin Jenness

Kevin Jenness

Joined
Nov 15, 2020
Messages
818
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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.
 
I just started mixing my own shellac using 99* isopropyl alcohol and find that that mix raises the grain much less than the Zinzer product I had been using.
 
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.
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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.
 
For endgrain saturation...are you guys continuing to put shellac on until it stops getting soaked in?

I learned a while ago, that if I do that, I often don't stop for a long, long time. I found that putting a couple of coats on engrain that keeps soaking, then letting it dry for a while, then coating again, usually greatly reduces the amount of total shellac that gets absorbed by the endgrain... At least, with many woods, not sure if this is true for more open-grained woods.
 
I've always used denatured alcohol for cutting shellac, for over 45 years now.
I've used it for french polishing furniture, to seal pine knots, as a sanding sealer on turning and as a final finish.
Save the rubbing alcohol for your sore muscles and get so good DA.
 
Omer Klee said:
I've always used denatured alcohol for cutting shellac, for over 45 years now.
I've used it for french polishing furniture, to seal pine knots, as a sanding sealer on turning and as a final finish.
Save the rubbing alcohol for your sore muscles and get so good DA.
Click to expand...
If only it was that easy. It's hard to find up here in canada for some reason. I can find some alcohol stove fuel which is basically denatured ethanol which I use and have no real issues. Denatured alcohol seems to be considered too dangerous here, Ironically I can buy pure methyl hydrate, far more dangerous, at any big box store....go figure.
 
Jon, if I'm just using it as a regular sealer I brush a good bit on, let it cure for about 30 minutes then maybe go back with another. I'll be turning a bit more perhaps or sanding so not worried about what it might do re any wood movement. Just want it on as a sealer but I don't keep at it until it stops going in. Experience is it will just keep soaking it in. I want the first application to soak in a bit then harden. On all my hollow forms I use it on the bottom as a sealer after I sign them but you're correct. It will seem to just keep soaking it up as long as you keep putting it on. I rub or lightly brush on, let it cure a bit, then maybe another coat where it needs it but not too much. Just looking to provide a bit of protection to the bottom and seal in where I signed it. Experience is a heavy soaking on the end grain of a hollow form will cause some distortion that might be enough to cause the piece to wobble on the table.
 
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