I have been finishing a table with Shellac. It is Oak and I filled the grain to get a flat smooth finish. After applying the first coats (HVLP) I realised that some of the pores on the edges didn’t get filled. I planned to lay down numerous coats, level with sand paper and buff to a hand rubbed finish; so I figured I would just have to add a couple of extra coats to fill in the pores. Well after 6 or so heavy coats followed by sanding I still couldn’t fill the pores. It seemed that the surface tension of the Shellac caused the finish to not flow into the pores. Next I tried using a brush. That did it. The brush would get the finish into the pores. I applied a couple or so heavy brushed coats.
All this took place in a two week period and after I started using the brush it seemed that Shellac wasn’t hardening like it should. I didn’t really worry too much about it since I knew I would sand most of it off anyway, and I have laid Shellac on very thick before and it always hardened properly. Well it has been three or four weeks now and it is still gummy. It clogs sand paper very fast even with liberal use of Mineral Spirits. I have been using scrapers to remove the gummy finish. The scraper is even prone to sticking to the surface causing deep marks. It is not sticky, really it is more soft than gummy. I have applied gallons of Shellac and never had a problem like this.
It has been very cold here in Dallas (for Dallas). It got down to freezing for about a week and then again for a few days. I started heating the finish room but that was after the first freeze. I never heard that Shellac is sensitive to temperature… but the problem seems to have started about then. Another clue is that the bottom of the table, which has fewer and thinner coats applied only with the gun, is fine. I think that all those coats were applied before the freeze.
Here are the answers to your most likely questions or possible causes:
It is Zinzer’s blonde Shellac the date code is Oct. ’06.
I was thinning it for the gun but brushed it straight from the can.
I used a lot mineral spirits when sanding. Some would penetrate into the wood so I waited 24 hours before laying another coat after sanding. I am sure it all evaporated. And it didn’t effect the sprayed coats on the bottom.
The first couple of brushed coats were very thick, and I brushed more over the not completely cured previous coats. I figured it would all harden eventually. Ive done this in the past with no issues but that was during the summer.
I am guessing that the cold may have caused the problem. Have any of you Northerners had that problem?
I will try putting a thin coat on a scrap piece of lumber tomorrow to see if the finish is bad.
Honestly I keep thinking that “today it will be hardened”, but no dice. Maybe tomorrow….
This problem has upset a customer because I have missed the deadline twice now.
Thanks for your help,
Mike
Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don’t have. You won’t regret it.
Replies
Shellac should "cure" within hours. And subsequent coats should amalgamate with previous coats to form "one" coat. In spite of the date on the can, it sounds like it is "old" and won't dry.
Shellac is easy enough to remove and start over fresh. Remove with denatured alcohol.
Why the thick coats?
I understand the nature of Shellac's drying process. That is why I avoided the word "cure" because technically it dosen't cure, but I think you know what I meant. I applied the thick coats to fill in the grain where the filler missed. Also by using the brush I was able to break the surface tension thereby allowing the finish to flow into the pores. I have done the same thing with my HVLP system with no problems. I might lay down two or three good coats within an hour and then let it dry overnight and the next day it is good to sand. But the HVLP (turbine powered) heats up the finish and dramiticly speeds dry times.
Sounds like you don't think the cold weather is to blame. I am going to check the Shellac today on some scrap material.
Thank you for your help.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
I see that you used a filler. Oil based filler is extremely slow curing. Even under good conditions (upper 60°s or higher and low RH) it takes days to cure -- I always allow a week before top coating. With temps below about 50° it's curing slows to a snail's base. The end grain on the edges may have soaked up a lot of filler that hasn't cured and that I am guessing that may have something to do with the problem.
I would follow Gretchen's advise to strip off all the shellac and start with fresh. Zinsser's says its shellac should remain fresh for several years after the date on the bottom of the can. But,... With shellac, if you can't sand it to powder after overnight something is wrong. That's the sign to stop, and not apply more coats.
I'm a bit confused about something else. You say you used blonde shellac. But Zinsser doesn't market any of its product as blonde. (SealCoat is nearly blonde in color, but I don't think Zinsser calls it that.) It does sell a light colored shellac called Clear (which used to be termed white shellac). Clear shellac has been chemically bleached, a process which tradtionally reduces its durability in use and the time it remains fresh. (That's why you see no bleached shellac flakes.) Blonde shellac is a light variety of orange shellac with the dye removed mechanically I believe, not bleached with chlorine. Your liquid shellac should still have been in date, but with bleached shellac there may be more complications with either temperature or with filler.
It is water based filler. The stuff made by elmers. I mix it with water based stain to achieve the perfect colour. I always test a new batch to make certain that it will harden like it should. It hardened in a few hours. It was more than 24 hours before the first coat of Shellac.
You are right about the Zinzer Shellac. I get their products confused because I use a lot of their pigmented Shellac as well so I just described the product, rather than give the wrong name.
Another posible culprit (linked to to the bleaching process damaging the shelf life) is that I transfered the finish from the can to a plastic half gallon mixing container because the can is too small to brush out of. I have kepted the lid on the container when not in use, but the finish is exposed to a lot more air inside the conatiner because it is only 1/3 full and a lot of surface area of the Shellac is exposed. Since it is Oxygen that causes shellac to go bad I wonder if putting it in this container caused a problem. But again this is something that I have done several times before with no problem.
Now I wished I had just used Nitro Lacquer. It has finally warmed up here so I am, once again, hoping that when I go to the shop everthing will be fine.
I noticed that you too didn't mention the cold weather as an issue for the Shellac. Maybe it is a bad batch.
Thnaks for the help.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
Well, the finish dried normally on the test piece.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
mudman,
Well I think you answered your own question.. shellac normally dries real fast. One of the great things about it.. Because I over thin shellac to get smooth brush free finish I've never had it cause any sort of problem. I would never, ever use directly from the can.. 15 minutes & you should be sanding I've never had weather affect it's rate of evaporation..
That's interesting. Since the same shellac dried OK on this other example,it must mean there was some kind of interaction between the filler and the shellac. (If I got it right, the only thing under the shellac was filler tinted to the desired color.) This is an acyrlic based filler. The Elmer's web site contains nothing at all in the way of application instructions, but your problem with the cold may derive from the filler.
I suspect the binder in the filler is something like a waterborne varnish. Acrylic varnishes usually won't work at all below about 55°, give or take, because the material won't coalesce properly--I've seen it bead up in lumps. Acyrlic varnish doesn't only dry by evaporation of the water. First the water evaporates letting the little "packets" or latexes of the varnish coalesce and begin to cure chemically. Cold interrupts this process so that waterborne varnish at least is quite temperature sensitive.
Does the label on the filler say anything about temperature?
Mudman: Shellac should be applied as a thin coat. See what pound cut the can is and it probably should be thinned with denatured alcohol. I am not an expert but I went to a workshop by Don Williams from the Smithsonian Inst. and he uses a 1 lb cut. I've also read in a Taunton Press book on finishing about using a 1 1/2 pound cut after a one pound initial application. The can wll tell you the cut and how do reduce it.
Gary
Shellac is generally easier to apply cut to between 1 lb. at the wash coat end, and 2 lb. cut. But it certainly can be applied at 3 lb. cut, and will dry just fine in usual circumstances. It's just hard to apply it well at the heavier cut. But cutting is for application, not because it needs to be cut to dry. The drying problem in this thread was almost certainly caused by something else.
Thanks for your input.
I too am lost. I can't imagine that such a minute amount of filler could cause a problem. But the only difference between the top and bottom (which is nice and hard) of the slab is that the top recieved a few heavy coats, and the use of a filler.
I tested the filler to make sure it would harden before I used it...no problems there. I don't think that it was very cold during that time either.
How about this...... I was using the minerial spirits liberaly to keep the sandpaper going. Perhaps the minerial spirits was absorbed by the filler causing it to go back into a paste like form then as it recures the offgassing causes the Shellac to go bad.
That still sounds like a stretch. At any rate I am going to scrape it all off and start over. The only real bad thing about this is my client is very dissapointed. I took this comission as a "something to get done when you can" type a thing. Well yall know how that works.Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
I would still remove with denatured alcohol rather than scrape. It is quick and with this, should be relatively clean. And probably very little sanding needed.Gretchen
I have brushed Zinsser shellac and zinsser seal coat just as they come out of the can. No problems. Part of what I did was covering large surfaces like floors and woodwork, requiring gallons of the stuff.HOWEVER, while the seal coat dries in 45 minutes, each subsequent coat takes longer. I am not sure why this is, but would speculate that the alcohol carrier softens up the lower layers and then takes longer to get back out. Whatever the case, I have had to wait for two or three days for the third full-strength coat to harden tot he point that it was not tacky under pressure. I learned this the hard way by putting sock prints in a floor.BTW, according to them, it is not fully "cured" for several weeks, and is therefore not as hard as it will become.Zinsser has a a shelflife guarantee of a year or so.
Couple of points. I have used a lot of shellac and the basic rule is that shellac should be applied as a thin finish and it should not be built up to much more than a 3-4 coat film thickness. Particularly if using a dewaxed shellac, a thick coat will have the outside begin to harden while the inside still contains it's solvent. Because of the gouter layer hardening, the evaporation is significantly slowed.Shellac has a very small amount of solids and does not work well in filling grain.I know you say you have applied thick coats in the past without a problem but my experiance is that thick applications can lead to problems.Howie.........
Well, it turns out that it was the most obvious cause. For what ever reason the 3 month old (according to the date code) is bad.
The test coat I applied to the scrap mostly absorbed into the wood making it hard to tell if it hardened, so I applied two more normal coats last night. Guess what?................. It is soft. I am so pissed over this. I spent all night stripping the many layers of the table top. I am glad that I didnt apply any on the bottom; it is curved and has a pattern of carved scallops that would make scraping impossible.
THank yall for the help I doubt that I would have double checked the finish by adding more coats if not for yalls input.
Mike
Pardon my spelling,
Mike
Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.
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