I’ve made a box with inlaid lettering on the side – combination of maple, walnut and jatoba. I brushed on a 1lb cut of shellac and waited about 6 hours. I then tried wet sanding it using 400 grit silicone carbide paper with mineral spirits as the wetting agent. This created an awful white powder that got into all the pores of the walnut. A quick rub down with lots of alcohol saved it, but . . . what caused this?
I’ve looked at a couple of references and all that I can find is a reference to “corns” forming on the sandpaper that will mar the surface. I did not see corns, just that the black sandpaper was covered with a white powder.
I mixed up the shellac from flakes about 1 month ago – so I doubt that the shellac is the problem.
Any help would be appreciated!
Thanks
Mervyn
Replies
It's just the fine sanding dust from the shellac. A quick wipe with alcohol will take care of it.
Mike Hennessy
Pittsburgh, PA
Thanks for the help.
Would this still happen if I had let it cure longer, or does this always happen with shellac? (This is the first time I'm using shellac, mainly b/c I'm trying to avoid oil that will yellow the maple.)
Thanks
you are going to get shellac "dust" from sanding. But if you sand it dry and brush off the dust (you can use a new paint brush) there is no mess.
Mervyn,Shellac sanded with a medium (water, etc.) turns the dust white. You can just brush it off and put on another coat, the dust will remelt and blend in. However, after five years of trying to apply shellac by the book, and usually being frustrated or confused, I finally took the time to experiment a bit and now I feel much more in control. The experiment only took a couple of hours...french polish. The key thing I learned was if I don't like it, I can flush with alcohol wipe it down and start all over.I'm going to try to attach a french polish protocol that someone was kind enough to post here on knots. It may sound very strict and invloved, it's really not. The first mistake i made was taking it too seriously. The second go around everything cam out really beautiful. Most importantly, shellac may become your favorite finish.
Thanks for the post!
My grandfather was a cabinet maker, and "french polishing" always had this aura of mystique and craftsmanship about it. I've been woodworking for a year now, and tried a french polish using one of Jewitt's finishing books a month ago, and it did not work out at all. Tthere were so many areas that it could have gone wrong that I did not know where to turn.
Your attachment looks like it has much more detail - thanks. I look forward to trying it out soon.
Mervyn
Mervyn,
Don't worry too much about the white powder. It's the high spots coming off the coat of shellac.
I would recommend a 2 lb cut, 3 - 5 coats, then rub"LIGHTLY", (and I do mean LIGHTLY), with the 400. Apply another coat or two and start to rub with 800. Remember, each coat of shellac dissolves the previous coat, so leveling is pretty easy if you don't slop it on.
I'm no expert, but if you use a 1 lb cut and rub it with 400 paper there's probably little shellac left.
I've never had any luck rubbing a shellac finish with alcohol. The English call that "spiriting off", but it hasn't worked well for me.
Practice on some scrap, keep trying and don't give up. Applying a nice shellac finish is a learned skill, just like everything else we do in the shop. Good luck, have fun and post some pictures of your success.
Fred
As the others have said, the white powder is the "sanding dust" from the shellac. It's a good thing--it tells you that the shellac has dried and is fresh enough to sand to powder.
But, as Fred pointed out, a coat of 1 lb. cut shellac has built an almost negligible film. Shellac has very low solids, and 1 lb. cut is very thin shellac. A little higher cut--1 1/2 to 2 lb. cut is still easy to apply but builds at a little better rate.
You do not need to sand between coats of shellac--they adhere perfectly well with no sanding at all. The only reason for sanding is to remove defects. So, as Fred says, apply several coats--they will all meld together, and then lightly sand, using a sanding block, to remove any defects, taking care not to sand through to the wood. I recommend 320 grit, though 400 grit is OK, and I recommend using it dry. Yes, paper may clog (corn) a bit, and so you will go through a lot more paper, but the dry sanding allows you to see much more precisely what is happening. It will take a number of coats before there is enough film to allow a real rubbing out process. You don't want shellac to end up with a thick film, but you may need quite a few coats to get to the point where you can level the surface and rub it out to a smooth finish. Much depends on the look you are aiming to achieve.
It will depend quite a bit on what kind of wood is being finished. The open pored woods such walnut will take quite a few coats to fill to level, while the maple will start to build after a few coats.
Heck, I usually leave the powder in the pores to act as a grain filler. The white(or amber color as I use amber shellac) color will dissappear once the next coat is applied. I've never heard of using mineral spirts as a wetting agent for wet sanding shellac. That doesn't sound like a good idea to me and all I ever use dry sanding until the final coat then i'll use wax and steel wool.
Mervyn - As others have said, a single coat of shellac isn't nearly enough to sand smooth. Moreover, 400 grit is pretty aggressive for sanding a finish - while the white dust you observed is probably mostly shellac, it may well have had a good bit of wood dust in it as well.
I do this a lot on small boxes, small stands for bonsai trees, etc..., and I will typically brush on 5 coats of a 1.5 lb. cut of shellac before any sanding. I use an artist's brush for this, as it leaves considerably smaller brush marks than a "paintbrush". You can pick up a 1/2" artist's brush made of taklon bristles for about $20. It's worth it, and with shellac, there's no danger of ruining the brush from dried finish - just soak the brush in denatured alcohol, and any shellac buildup will re-dissolve.
You may also want to "dry-sand" - you can do this by getting some stearated aluminum oxide sand paper. The zinc stearate in the sandpaper lubricates the sanding action without having to use a liquid lubricant. By the way - probably the best liquid lubricant for sanding shellac is water with a -little- bit of hand dishwashing detergent added.
Finally, you'd be surprised how quickly shellac will deteriorate in solution. In my opinion, one month is really pushing it, and shellac's too cheap to try to save a little money by using an older solution. Mixed fresh from blonde shellac flakes, it should be dry to the touch after about a minute or so. You can reapply another coat after 5 minutes, and it's sandable after about 30 minutes.
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