cured shellac questions

Hi -
I applied about three coats of shellac to a tea chest almost four weeks ago. I imagine the shellac has cured (the box has been at 60-70 degrees F the entire time). I had planned to rub out the finish but I need a few more coats before I can do that. So I'm wondering, if the shellac already on it has cured and if so, what happens when I apply fresh shellac over it (or should I)? Will it fuse to the cured shellac or is shellac that's cured no longer able to meld into another coat? Should I strip off what shellac I can and start the coats over until it's built up to where I want it?
Mike
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wrote:

the next coat will melt into it- forever.
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Crawled out of the shop and said. . .:

shellac is great in this regards because it never really cures when DNA, or fresh shellac is applied to it... one of the reasons its an almost foolproof finish...mar it up, rub it out with fresh alcohol and shellac...
so in essence, shellac has 100% burn in at any time.
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Wipe it down with mineral spirits to get any interim nastiness off, and coat away. As others indicate, it'll chemically bond.

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Shellac never "cures" like varnish does. It is always dissolvable by it's solvent (alcohol) or the next coat. Just clean it off & apply more coats til you get the thickness you want. It will be fine.
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Larry Wasserman Baltimore, Maryland
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As others have noted, shellac is a "hot" finish - each new layer dissolves the surface of the previous layer, as opposed to poly where each new coat merely sits on top of the previous layer. Sanding between layers of poly provides a mechanical connection between the layers.
On my current project I'm shellacing parts prior to assembly, being careful to avoid areas that will be glued or sanding those areas to bare wood later.
Got carried away on a pull out shelf - probably applied 15+ brushed on coats of one pound cut shellac in 30 -45 minute increments. The garnet shellac made the cherry ply shelf appear golden without obscuring the grain. Liked that look so did the same on the sides and top of a pull out box that will hold Scary Sharp plates. The finish looked glorious!
Let the box sit for a couple of days in a 60-75 degree shop while doing other parts and dry fitting things. When all the parts were ready and the whole thing had been dry fit just to make sure I hadn't miscut something, I set up the clamps, glued things together and clamped them snug but not tight.
Four hours later I removed the clamps - mainly Bessy K-bodies. Everywhere the clamp faces contacted the finish I got jaw imprints - not deep but noticable on the nearly glass smooth finish.
So the question is - To get a nice hard shellac finish - how long between coats with a 1 lb cut? - how long after final coat before the finish is hard enough to clamp without imprinting the clamp jaws into the finish (assuming 60-75 degree shop with 75-80% RH?
I really like the range of looks you can get with shellac Thin coats are quick and easy to apply, it loses its tack quickly so dust is less of a problem and the finish builds fairly quickly. . I also like prefinishing parts so the finish can be applied with the parts laying down flat.
But if I want a thick, deep prefinish and have to wait a week or so before clamping ...
charlie b
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I think you need to rely upon cauls, blocks or clamp pads of some kind to prevent the marks, not the finish.
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Lawrence Wasserman wrote:

I did use rounded edged redwood "pads" on four of the clamps and they left imprints. I also used the twin cam/one movable "jaw" clamps for the face frame - no way to pad them. They're rubber jawed. Still left imprints in the finish.
charlie b
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charlie b wrote:

Well, Charlie, I'm a shellac newbie. The only stuff I've used is the Bullseye stuff with all the shelf life extenders in it.
I have no idea how hard it's supposed to get, or how hard real shellac gets, but this stuff in this can I have (had, actually) never cures hard at all. I've got a piece I finished in November, maybe 10 coats with a 1# cut, and if I rest an arm on it, the fabric of my shirt leaves an impression that won't buff out.
I think in my case I very likely got some bad shellac, but still, based on what experience I do have, I sure wouldn't characterize this as a hard finish.
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On Wed Jan 21, Silvan disturbed my nap when he said:

Shellac gets good and hard. If it didn't you'd never be able to rub it out. Maybe you should consider using flakes. Far more economical and flakes have many, many years of shelf life (unlike canned). You only mix up what you need, when you need it and put them back in the fridge...
Mike
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Silvan wrote:

With "Bulls Eye" shellac I find the finish will remain soft unless the wax is removed before application. Did you decant the wax from the shellac before using it?
I mix it 50/50 with denatured alcohol, let it sit for 2-3 weeks and then pour off the clear liquid for use and discard the rest. It yields an approx. 1.5 pound cut.
Another option would be to buy the "SealCoat" which is already dewaxed.
-- Jack Novak Buffalo, NY - USA (Remove "SPAM" from email address to reply)
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I've been using the "Bulls Eye" shellac on my latest project and haven't had any problems at all with hardening. In fact I have been able to sand without it balling up or doing serious clogging after only a couple of hours of curing. I found it worked better if I let it set overnight on heavy coats however.
I have read that shellac won't harden properly if it is too old. I assume the "old" counter starts once you open the lid.
Just out of curiosity, how hard is it to make the shellac from flakes? It looked like more trouble than it was worth compared to a $4 can from Menards.
Jim
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Jim wrote:

I suggest you try decanting the wax out of the Bulls Eye. The wax inclusion softens the finish, degrades the moisture/heat resistance and may cause adhesion problems when shellac is used as a base coat for other finishes.

The esterification process begins as soon as the flakes are mixed with alcohol.

Mixing shellac is not hard at all. For me the hard part is obtaining the flakes as I either have to order them or drive forty miles or more to get them.
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Yes but actually the "old" counter starts as soon as the solids contact alcohol.
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FF

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Nova wrote:

No, I didn't. I didn't read about that trick until it was all said and done.
I think for my next batch, I'll go ahead and get some flakes though.
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I think iT might be bad too. Tony D. "> I have no idea how hard it's supposed to get, or how hard real shellac gets,

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Yep, Shellac is pretty soft. I like it though. "Think I'll go plane a piece of scrap wood, cant build nothing right now. " Tony D.

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