How do you sand shellac without the paper corning up in seconds?

[Dan Friedrichs]

I've been using multiple heavy coats of shellac as a neutral grain filler on several projects. I like it. My only problem is that when I go to sand it flat (in preparation for the top coat), my sandpaper develops "corns" within literally seconds of starting the sanding. I feel like I've tried everything to avoid this, but it never changes. Things I've tried:

1) Both premixed (SealCoat, fresh) and freshly made-from-flakes shellac, both dewaxed
2) Sanding with a ROS (Festool 125 with dust collection) and hand sanding
3) Turning the speed down on the ROS (which helps a little, but not much)
4) Different types of papers
5) Sanding shortly (~12hours) after the shellac, or waiting weeks before sanding
6) Letting the work sit in my low-humidity 70F house, or freeze in the garage

...nothing seems to make any difference. The corns obviously reduce the speed of sanding, but more problematically, they create high spots on the paper which then effectively act as single particles of much larger grits, gouging the surface.

It seems like other people do this successfully - for instance, in this thread, Per recommends using the Festool Brilliant 2 papers on a heavy layer of SealCoat. That's exactly what I'm doing - so what am I doing wrong?

[Prashun Patel]

Wetsand with mineral spirits.
On rare occasions I've been able to dry sand shellac without corning. But most of the time it requires wet sanding.

[Dan Friedrichs]

So you're doing it by hand, Prashun? I was hoping there was a method that involved my Festool toys

(I have tried this, but don't really like the mess and inability to easily check progress)

[Scott Holmes]

I use a scraper. Or you can wipe it with a cloth damp with denatured alcohol.

[John TenEyck]

Have you considered a transparent filler instead? Crystallac makes a WB one that has no color.

John

[Chris Fournier]

If you are using shellac as a grain filler, you just sand it back until it feels smooth and flat. I check progress with my fingers. Rubbing through is not an issue.

'Sanding' shellac requires only a pass or two with 220-400 grit sandpaper. You can sand a 4'x8' panel in about 3 minutes by hand. Hey, I have a Mirka Ceros and have an itchy ROS finger. But sanding shellac goes better/faster IMHO by hand.

This response has no reference to the OP's surface quality and is consequently not very helpful or accurate. 3 minutes to do anything meaningful to 32 square feet of finish is a bit fantastic by any measure.

As Scott suggests a card scraper can be very effective and efficient at taking down a hard finish be it dry schellac, varnish or cured lacquer.

[Prashun Patel]

Sorry. Forget i suggested it. Did not mean to offend or to be not helpful. I made a case piece last winter and hand sanded between shellac coats. All i meant to imply is that it isnt hard to hand sand. Again, sorry if i was out of line, chris. I wasnt lying when i said it went quickly.

[Chris Fournier]

Prashun,

I don't think that you are out of line nor offensive, you come across as a very reasonable person to say the least.

Shellac however rarely needs to be sanded because it is so easy to move around if you simply use more solvent - alcohol - to rework/apply it. This is the whole point of french polishing after all. Personally I'd use grain filler to fill pores unless I was after a french polished finish.

[sheldon pettit]

I disagree with ever sanding shellac except for repairs when really needed. Sanding/scraping/ or other removal is just a waste of the lac. Unless someone can explain to me "why" it has to be abraded or scraped, etc, then to me it will remain a waste.

[glenn bradley]

No power sanding. No heavy coats. Some good suggestions here. Also some comments that make me think I'm on one of those saber-rattling, chest-thumping, un-moderated forums where people are fairly adversarial as opposed to accepting and helpful. Many light coats with light sanding in between will work for using shellac as a filler. Certainly sanding any topcoat to remove nibs or other surface fouling aspect, if it occurs, is common practice in a home shop. Scraper, rag damp with alcohol, stearated sandpaper; all will work. Your build up on your paper is due to too much too fast. JMHO .

[Howard Acheson]

Here is a good write-up on the process of using shellac as a grain filler:

http://www.hardwoodlumberandmore.com...h-Shellac.aspx

Note that it works a lot better using a fresh shellac that you mix yourself. Old shellac does not sand well but using a scraper is better anyway.

[joe milana]

Here is a good write-up on the process of using shellac as a grain filler:

http://www.hardwoodlumberandmore.com...h-Shellac.aspx

Note that it works a lot better using a fresh shellac that you mix yourself. Old shellac does not sand well but using a scraper is better anyway.

12coats? I tried this method and it seems that when I sand back to bare wood, I just open up more grain. It's an awful lot of work.

I noticed it suggested to simply rub the finish with an alcohol soaked rag (as in french polish). Would this technique leave a smooth enough surface to accept a sprayed on top coat?

[Todd Burch]

When I try to hurry a shellac finish, I'll get corning, even with stearated paper. The more time you give it to cure, the less corning you will get. I think the freshness of the mixture makes a difference too.

Todd

[Jim Becker]

I disagree with ever sanding shellac except for repairs when really needed. Sanding/scraping/ or other removal is just a waste of the lac. Unless someone can explain to me "why" it has to be abraded or scraped, etc, then to me it will remain a waste.

The OP isn't using the shellac as a "finish", per se. He's using it as a grain filler and sanding back between coats until he has a perfectly smooth surface to continue whatever finishing regimen he intends to use for top-coating. And yes, that could be shellac...

[sheldon pettit]

The OP isn't using the shellac as a "finish", per se. He's using it as a grain filler and sanding back between coats until he has a perfectly smooth surface to continue whatever finishing regimen he intends to use for top-coating. And yes, that could be shellac...

Hi Jim, my intentions in what i stated and beleive and practice is the waste of shellac in doing such. If you want to use lac as a pore filler then you can just heat a spatula, as wide as needed or wanted, draw it across the wood surface and remove the excess while filling the pores. As long as the surface is flat, the operation goes as quickly as if filling a dent with lac sticks and removing the excess. Just be sure not to have the blade so hot it burns the wood, with a little practice, you an fill a 4'x8' sheet using a 6" spatula [stiff kind]in about 1/2 hour. after that, any thin film still present can be removed or taken care of by using a alcohol on a balled rag to make perfectly smooth ok?

If by chance you need the wood to be perfectly open, "then" you can use fine paper to take what little excess may remain off the surface with out wasting the bulk of your lac using other methods.

Another method i use is mixing 4-6F pumice with 3-4 lb fresh shellac and making up a filler and applying it and taking the excess off with a plastic card etc., with this method though you don't want to apply more than can be removed quickly say 1 sq. ft at a time at most. The Removed excess can then be put back in container, with a little alcohol, preferably anhydrous isopropyl, and used on the next job. Thus eliminating or drastically reducing the waste of lac being used and applied by other methods mentioned.