sanding shellac

Re: sanding shellac

Denis Ch�nard, Orl�ans, Ont.

>Two hours should be enough, I think your shellac is beyond its "best before" date...

There might be a date at the bottom of the can, check it out...

DC

Re: sanding shellac

Bruce, a MN Galoot

>As Denis said, check out the "best used before" date, but also I don't sand when I'm going to apply a top coat. Take a very sharp scraper and lightly run it across the surface of your new shellace. It makes very quick work of taking out the nibs and even high spots.

Bruce

an experiment

Bill Tindall, E.TN

>Now that a day has passed sand again. If it doesn't load your question is answered.

I see absolutely no need

James Watriss

>I never sand between coats.

Shellac has this wonderful property... laquer, does, too, though the solvent is different...

The alcohol the shellac is dissolved in will partially dissolve the surface of the previous coat. When it dries, the resulting finish will be one fully integrated coating. It also means that refinishing is a snap, once you remove waxes and whatnot, because the new coat of shellac will dissolve the edges of any scratches or damage to the finish, and help smooth things out without having to strip everything off.

With poly, or some other varnishes, it helps to sand between coats, because a fully cured first coat will have a smooth, even surface that will not be affected in any way by the second coat, and they won't necessarily bond as well as they should. Scuffing up the first coat allows a good mechanical bond between coatings, and, form what I understand, will blur the line between one coat and the last. Wet sanding (Sanding, while lubricating with more of the finish) works well, too, because the coat you're laying on will simply wash over the previous coat, and help lubricate the abrasive in a way that will really smooth things out. Try a wet sanding job with shellac, and you're likely to strip the finish down to the wood.

The only reason I might sand is if you have an area that is physically wavy, bumpy, or funky in some other way, and you need to mechanically level it out using an abrasive medium. That said, I think if it was funky enough to require sandpaper to knock it down, a razor blade might also do a good job of scraping it down enough. It would only have to be smooth enough, because the alcohol will dissolve or soften any small scratches and such.

Generally, the best thing to do to help the second coat of shellac bond to the first coat is... nothing at all.

Depends

Frank D. in Montreal

>Depends how you applied it. If you wiped it on, 2 hours should be OK, especially diluted (I assume you're using Seal Coat). If you brushed it on, however, it can take up to a day not to load sandpaper. I also assume you're using stearated (no-load) paper.

Re: an experiment

Warren in Lancaster, PA

>Thank you, Bill. My first reaction was that the coats were just very heavy.

Bob, I am not sure what you mean when you say "diluted by 1/3". There is a big difference between adding 1/3 cup of alcohol to a cup of shellac as opposed to adding 1/3 cup of shellac to 2/3 of alcohol. I would recommend the latter, especially for a beginner.

MS and Wet 'n' Dry Paper

Mike Fitterling

>I agree that you do not have to sand between coats of shellac. That said, I often wet sand using mineral spirits as a lubricant right before the last "coat" to remove dust nibs and any other imperfections that might have surfaced. If you use MS and wet 'n' dry sandpaper you will not have the loading. Wet sand and wipe dry. I have done this with shellac and between an application of shellac followed by lacquer (I do the next to last coat of laquer the same way, too) and have never had any adhesion problems or excessive paper loading.

Cheers and good luck,

Mike

What about dry sanding?

GolfSteve in Calgary

>What about when dry sanding? I always have lots of loading when dry sanding shellac, even using Norton 3X or similar high quality paper.

This weekend I sanded some shellac coated panels that had been sprayed three weeks ago. The 320 and 400 grit paper loaded up pretty quickly.

My impression, with limited shellac experience, is that shellac loads up sandpaper very quickly. Using light pressure and blowing off the swarf seems to help, but it still forms little kernals very quickly.

I'm asking this question because someone suggested that the shellac might be bad, causing loading. My first experience with shellac produced a very soft finish, which someone suggested was due to bad shellac. I've bought new flakes for the current project, but the shellac still seems soft to me (ie. if I leave something sitting on the panel, it will leave an impression in the shellac).

my experience

Bill Tindall, E.TN

>My experience with shellac is not great but everything I have finished dry sanded just fine, in fact better than any other finish. I only hand sand. I can see that with machine sanding the shellac could get hot and hence soft. I use stearated paper, in range of 320 to 400 grit.

Re: What about dry sanding?

Dan Donaldson

>I would say that if you can sit something on the shellac and it leaves and impression after the shellac has had time to dry, there is something wrong. Try putting a drop of the shellac on a piece of glass, let it dry, then scrape it off. If it is good, it should flake off. If it stays soft, then something is wrong with it.

Re: sanding shellac

R.J.Whelan - Sierras, California

>Bob .... one thing that will help with "loading" is to use "stearate" paper. Basically this paper has some form of soap as part of it's manufacturing process; the soap acts as a lubricant. I buy my paper from Klingspor and have been very pleased with it's performance - you will get some loading but not nearly what you'd get with non-stearated paper.

I usually give shellac an "overnight" cure before sanding or rubbing out.

I will generally apply two initial coats of shellac (without sanding between 1 & 2) and then rub out all subsequent coats. The exception to this rule is if the first coat causes grain raising; in those cases I will knock down the raised grain before applying the 2nd coat.

If you use prepared shellac you can test it's usefulness by putting a drop on the lid of the can (or a piece of glass): let it cure for 24 hours: if you can make a mark in the cured drop with your thumbnail I'd recommend against using it.

Good luck ......... rj