RE: Shellac Printing

>>Could this finish still be soft? 
>>Had it not cured enough? 
>>Will it ever cure? and how long will it take?
>>What would you do!?



Bill, 

This is another one that will probably get a bunch of answers.

Yes, the finish is probably still soft.  You got way too much on there, too 
fast.  Shellac goes on best in thin coats, and a wet coat (4 mil +/-) of 3 LB 
shellac should cure overnight at before recoating.  8 coats seems like way 
too much, too, which compounds the problem.

The bad news is, it will still take quite a while to cure out hard.

The good news is that you probably have plenty of material on there to sand 
out and re-polish.  I'd wait about 90 days, though.  The worst of the damage 
is already done.

Michael R
KC

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Russ Ramirez responds:


> they got some "plate marks" where the plates had been. 
> They said they used doilies as placemats.


White circles/ovals from sweating or rings?


> Could this finish still be soft?


Yes. Too many coats too quickly in my opinion.


> Had it not cured enough?


Basically yes. But it depends on the answer to my question because white
moisture blemishes could have occurred on a 30 yr old shellac finish
depending upon the exact circumstances. Earthenware for example seems 
to be rather prone to steaming finishes...

> Will it ever cure? and how long will it take?

Sure. Shellac retains solvent quite well however. Films as thin as 0.1 mm
have showed a 15% retention of alcohol after two days. As layers are piled
one upon the other, the retention of the lowest layers is going to be
enhanced by the presence of the upper layers - hence my comment about 
the number of coats in the given time-frame.

> What would you do!?

Strip the shellac and use a post-cat lacquer. Well...you asked :-) I love
shellac, but each finishing material has it's great applications and those
that probably should be avoided.


Russ Ramirez


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Jim McNamara writes:

Cured only skin deep.

You do have a problem. You have to extend recoat intervals as you spray 
more coats of shellac, most especially for deep build, high solids applications.
The shellac was nowhere near fully cured when you shipped the piece.

I also wonder about 8 coats? - that's probably close to 18-20 dry mils of
film - pretty thick.  Assuming you spray 5-6 wet mils each time.  Probably
looks great, but you discovered the price of really deep build with shellac.

When you spray a high solids coat of an evaporative finish (like shellac) ,
say 4 wet mils, the first coat dries to about 95% in an hour or so,
depending on the solvents.  But, as the finish builds the drying time
between coats has to extend because you are now getting solvent diffusing
deep into the old film layer with each new coat (burning in), so it takes
progressively longer for the solvent to get out.

With 8 coats of 3# shellac, you need 4-6 weeks of final cure time with the
schedule you gave us- if it really ever would cure.  In fact, as you added
coats, you should have extended the recoat interval significantly for each
new coat.  For the last 2-3 coats the interval should have been 3-4 days
between coats.  Then a final cure of  about 2 weeks.

I think if you had tried rubbing the finish you would have found it was
nowhere near cured when you shipped it.  Would have corned like mad.

If you want to have deep builds like that, consider spraying less solids per
coat, and extending the recoat interval for each succeeding coat.  Start at
abhout 1-2 hours, extend the interval by about an hour after the first 2-3
coats, then move up to overnight and longer as the film builds.  It really
is not an economically sensible schedule.  I'd charge a heck of a lot more
to do it than for lesser build.

Jim McNamara


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Too much shellac. Shellac cannot be built up like nc lacquer. 

Assuming you only single passed and didn't double pass, you probably have 
at least a 4 mil dry coat. Shellac retains alcohol for a time and thick coats 
really exacerbate this. In fact, had you done this with dewaxed, it probably 
would have crazed as well. It will eventually cure like any finish, but two days 
is pushing it for any finish except maybe Duravar.

Jeff

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Hey Bill....don't ya just hate that??...I think that the existing old finish and 
patina was probably broken down enough and grimy enough not to be a 
good under caoting for fresh shellac....and I think that 8 coats is probably 
just too much material...did it really need that much shellac?? especially 
considering that you left the original finish pretty intact and the grain was 
presumably closed .........? Sounds like a time when you could've just 
fp'd...and brought it up with that......I think it will eventually cure.....
but it may get too printed before that time....

GregS


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