Why is my shellac drying so fast?

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ttalma

ttalma

Well-known member
I am putting down some Shellac and it is drying very fast. I'm Getting a good finish and it looks good but I really have to move to blend the brush strokes. It is taking about 15-20 seconds from apllication, to being very sticky, (by sticky I mean causes a mostly unloaded brush to drag) and about 45 seconds until dry to the touch.

I am using super blond dewaxed shellac flakes. I have used the flakes from this bag before (several times in fact) and usually get about 2-2.5 min until very sticky and about 15-20 min untill dry to the touch.

It has been about 80 degrees every day and humid here. I am using a 4 lb cut. Using a golden taklon 2" brush to apply.

I've been appling the same finish to my test piece, and the bond seems to be good and the end result looks like good. Am I having a problem or should I just expect this on hot humid days? I would have expected the humidity to slow things down.

If I mixed it wrong, could that change the drying time?
 
This is a cool problem. A 4 lb cut is pretty thick but there are other factors. You can use alcohol while you are brushing to alleviate drag. I keep a spray bottle on my finish cart and use it to load the rubber for french polishing. It makes it easier for me keep track off what's in the mix (a dash of shellac-three pumps from the bottle) but I also use it when brushing to load the brush with alcohol before I put shellac on it. This helps the brush to unload nice and evenly.
Ethyl alcohol (C-2 H-6 OH) and water are surprisingly similar. They mix together, obviously, but their boiling points are very close together, only about thirty degrees apart. The upshot of this is that as the temperature increases the molecules start to behave more and more like each other compared to the other end of the spectrum ( the melting point of water is 32 F, ethanol -174 F) so a hot humid day may have a catalyzing effect. For myself I will only try working with shellac when it's cool and dry or if I can get the shop down to around 65% humidity. Try more alcohol. This won't harm anything and it likely will solve the problem.
Fran
 
I've brushed yards of shellac. A 4 pound cut is much too thick. Even a 3 pound cut is hard to use except for maybe the initial coat. I brush a 2 pound cut, work quickly and it still dries fast. But thats OK, just work quickly avoid "fat edge", and after 15 minute or so just go over it again. I usually do 4 or 5 coats of a 2 pound cut one after the other, let it dry several hours, lightly sand to level it with 320 stearated paper and go at it again. Usually do this 4 or 5 times over a few days. I usually pad the last coat or two (completely prevents fat edge) and then use 0000 steel wool and wax.
There are probably as many opinions on how to apply shellac as there are woodworkers. This works for me.

Howard Steier
 
I think I may have the terminology wrong (usually do) when I say 4 pound cut I mean 4 parts alcohol to 1 part flakes. Is that a four pound cut? I would call a 2 pound cut 1 part flakes to 2 parts alcohol. Have I been mixing wrong all this time? with my 4:1 ratio I always end up with some undisolved sludge in the bottom of my jar.

My schedule is normally: 3 coats - dry overnight, 3 coats - dry overnight, lightly sand with 220 - 3 coats - dry overnight, lightly sand with 400 - 3 coats - dry overnight, I then evaluate the finish if it needs more lightly sand with 600 3 more coats. But usually I stop with the 12th coat.

This has always seemed to work for me gives a nice smooth finish without looking  thick. I've never done french polishing, so I haven't screwed that process up yet.

I agree Howard that there is no one right way to apply shellac. But I am always a student and am eager to learn from the experiance of others.
 
I always reread the mix on the package of flakes and always mix a 2 lb. cut. I am a french polisher so I am not really sure why I need a 2 lb. cut. I keep the shellac I am using in a small bottle with a hole punched in the screw cap. From this I put a few drops into the rubber and squirt a bunch of alcohol into it ( or visa versa). What do I have now? A 1/8 pound cut? At the beginning of this process the padding in the cloth is loaded with 2 lb. cut and very little alcohol is added. The process goes on with the addition of pumice (don't do this with cherry) and gradually larger amounts of alcohol until the grain is filled, a stage called 'bodying out'. This is about the equivalent of the first two or three brush applications and a good sanding.
The 2 lb. cut takes at least a day or two to dissolve completely and there is always something on the bottom. Garnet seems to be the least willing to become a solution and often requires rolling the jar around to facilitate dissolving completely. Waxed shellac, of course, always settles with the wax appearing as a heavily clouded shellac solution in the lower region of the jar.
 
"Cut" refers to the number of pounds of shellac per gallon of alcohol. So a three pound cut is 3 pounds of shellac per gallon. A simple way to remember mix ratios is to remember that a 1 pound cut is 1 oz. shellac for 8 oz of alcohol, 2 pound cut is 2 oz per 8 oz alcohol, etc.
Now when it comes to mixing by volume, the results are inexact but here is the approximation that I was tought by Eli Rios. If you fill a jar with shellac flakes and then cover the flakes with shellac, you have approx a 3 pound cut. So if you are mixing 4 parts alcohol to 1 part shellac this is probably around a 1 pound cut or less.
I usually mix dry flakes. But sometimes, for convenience, if I have a small project I'll buy premixed Zinnser's Bullseye shellac (Home Depot or Lowe's) This is a 3 pound cut and can then be diluted as needed. Dissolved shellac has a shelf life so check the date stamped on the can.

Howard Steier

 
Tim - 45 seconds until dry to the touch is the way shellac should behave.  If the dissolved shellac mixture is old, it will take longer and longer until it won't harden properly at all.

If the alcohol has a significant amount of water in it, this will also slow the drying and hardening of shellac, and will substantially reduce the dissolved shellac's shelf life.

Finally, shellac flakes that have been exposed to high heat and humidity will often not completely dissolve, and the coat that's been brushed on may not harden as well as it should.

If you've recently changed the container of denatured alcohol that you're using, what you may be seeing is that the fresh container doesn't have as much water dissolved in it.  DNA will absorb water from the air until it forms an azeotropic mixture.  For ethanol, that mixture is 95% alcohol, 5% water.
 
It's good to know that my shellac is behaving correctly. That explains why I am able to get a good finish with it. I store the flakes in a cabinet. So they get up to room temperature. I heat my shop to 60 in the winter and only run the AC when it's over 90 in there (which it hasn't been yet).

I usually throw out mixed shellac once the project is done, unless I know I will be using some soon. It's normally to long between projects for me to trust the shelf life and a few $ worth of shellac is not worth ruining a piece to me.

I think the key is the alchol, I had to buy a new can for this project. The last can was over a year old. I've dated this can, is there a shelf life or any way to check the water absorbsion? Does it matter other than the drying time?

Next time I mix some I'll measure the quantities. I usually eyball it. I'm curious to see how far off I am.
 
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