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+-- Thread: Shellac not hardening enough (/showthread.php?tid=7329271)
Shellac not hardening enough - KingwoodFan1989 - 04-05-2017
Okay, so on a project I've been having a lot of finishing issues with, I've encountered yet another problem...the shellac, even after about 2 weeks, isn't even close to being fully hard. I can still dent it quite easily with my fingernail. I will say I did put A LOT of coats on, and I only waited probably 10-15 minutes between each coat, but you'd think it'd be fully hardened by now. This isn't old shellac, either. What's weird is it even seems to be a bit softer than it was a week ago. I tried sanding it a week ago, and I got a LITTLE bit of smearing in a couple of spots, but other than that I was getting a fine powder. Now I got a lot of smearing. The weather has gotten hotter in the past few days, so could that be it? What's going on?
Boy is finishing frustrating...
RE: Shellac not hardening enough - jteneyck - 04-05-2017
I'm not sure why it's getting softer, other than polymers usually soften as temp. increases, but you went way wrong by applying a lot of coats in a short period of time. Actually, a lot of coats over any period of time is a big mistake with shellac. Shellac will only give problems if you build it up to a thick layer. The thinnest layer that gives a continuous film is the amount to use; generally that's a couple of brushed on coats at 2 or 3# cut, or 3 to 5 wiped on coats. Think really thin. Shellac is not like varnish.
Either sand it flat and thin, or strip it off and start over. Think thin.
John
RE: Shellac not hardening enough - KingwoodFan1989 - 04-05-2017
Yeah, I put on WAY more than 3 to 5 coats. My reason for using shellac is that it doesn't form separate layers like varnish usually does. That way, any imperfections can be easily corrected and there's no risk of sanding through one layer and getting an ugly blotch. As for putting on the amount of coats I did (which I'm still hesitant to specify at the risk of getting laughed at, haha), the thing I'm finishing is a 20"x15" drum shell, so there's A LOT of surface area, and like usual with me there was a lot of inconsistency in applying the finish. I figured I would just be able to compensate for sloppy application by rubbing down the finish flat and polishing back up to a gloss without any issues. I've gotten the finish flat, but I need to wait until I get paid next week to buy some micro mesh paper that will work with my palm sander...my ROS is just too aggressive for this shell. It's a thin shell (at only about 5/32" thick), so I need something that will polish without vibrating the entire shell. I know I could do the polishing by hand, but with something this big that would take too long.
I guess my best bet would be to sand some more and then hopefully the finish will be thin enough to harden fully. There have been projects where I've done about 8 coats of shellac and they've hardened just fine. I've brought the shell inside and suspended it, so hopefully the more stable temperatures indoors will help it harden more.
RE: Shellac not hardening enough - fredhargis - 04-06-2017
Shellac can be frustrating to sand even when it's hard, if it's not hard it's almost impossible (paper clogs). You may have to move to stripping and start over. One word of caution (if that was premixed shellac): if the "fresh" shellac was bought at the local hardware, it may not be as fresh as you think. Around here some of the less popular stuff (shellac, plastic resin glue, a few other things) can sit on the local hardware shelf a very long time before being sold. The other thing, John hardly needs my endorsement, but the stuff about it being a finish that's best used in a thin layer is dead nuts. Even if it had hardened, you might have a wildly crazed finish over time. I think what happens with shellac is that folks sometimes apply to the same logic they would use with, say, varnish. It's a very different animal.
RE: Shellac not hardening enough - jcousins2 - 04-06-2017
rather than sanding - or at least before sanding - try using straight denatured alcohol on a rag and try to dissolve the layers - or at least melding them - maybe using a french polishing pad
jerry
RE: Shellac not hardening enough - Wildwood - 04-07-2017
I always thin can shellac and wait 30 minutes to an hour before apply second coat. Temperature & humidity effect drying times so may wait half a day between third or fourth coat. Normally only use 2 or 3 coats on closed grain wood on open grain do an additional coat. Normally only light sand after the first coat and not on additional coats unless needed.
Told by an experienced wood refinisher you have dry to the touch, dry enough for re-coating and fully cured times. Also too many coats of any film forming finish (lacquer, poly, shellac, varnish) equals very soft or brittle finish.
Even though each coat of Lacquer or shellac melt into the previous coats of finish more coats you add increases fully cured time! This is also true of your other film forming finishes. Used to work part time at that place and learned to finish the finish with mineral oil & pumice, didn't micromesh back then.
Like already posted already might try removing some of those coats with denature alcohol versus trying to sand..
RE: Shellac not hardening enough - Rob Young - 04-07-2017
Just to confirm the batch you are using hasn't gone bad (canned or mixed from flakes, it happens), put a dime to quarter sized puddle on a piece of glass or other slick surface and leave it overnight. It should cure and not be gummy. If it doesn't cure, the shellac may have absorbed too much water.
You say it isn't "old" but depending on how it was stored, what the condition of the flakes was (if mixed from flakes) or how much water had already absorbed into the alcohol used to mix it. It may take only a few weeks to go bad once mixed but should otherwise last 6+ months from flakes and DNA. 2+ years for the canned stuff. Store it in a place you would be comfortable sleeping. Not too hot, not too cold, not too humid.
Stripping with alcohol is going to be better than trying to sand off a gummy coating in my opinion.
RE: Shellac not hardening enough - Alan S - 04-07-2017
It will definitely take much longer to harden if you put on thick coats, and particularly if you don't wait long enough between them. There is a lot of alcohol that must find its way out for the film to harden, and a dry film is not very permeable. Nor is the very outside part of a soft film, so the alcohol gets trapped inside for a long time.
If you are in a hurry, use many thin coats, so the alcohol does not have very far to go to escape.
It is possible that your shellac is bad, but it's also possible that by using thick coats you simply increased the drying time from hours to weeks. If you have a warmer place to put it, that will help if the problem is trapped solvent.
RE: Shellac not hardening enough - KingwoodFan1989 - 04-07-2017
So I sanded down the finish some like John suggested earlier. My finer papers were heating up the finish too much rather than just mostly removing it, so I used some 180 grit and took it down quite a bit on a big part of the shell. I sanded through to the paint on one edge, so I put a few thin coats of shellac on that spot, and I doubt I'll do much heavy sanding on that spot anymore.
I got good results from the 180 grit, and although I'll have to go over it quite a bit with 220, 320, 400, and 600 before I get into the micro mesh papers, I have a surface that's fairly hard. It takes A LOT of effort for me to even put a slight, shallow dent in the finish with my nail, so I think I'll go over the rest of the shell with the 180 as well. Again, the amount of coats I put on in the first place is quite excessive, so I don't think there's much danger of sanding through to the paint on any other spots.
By the way, what it "crazing" with finish? I've heard the term. I just don't know what it describes. Thanks!
RE: Shellac not hardening enough - fredhargis - 04-08-2017
Sometimes referred to as "alligatoring" and maybe other names, it's basically just cracks in the finish that occur over time. Of the several possible causes, one of them is finish applied too thick.