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 (http://www.sawmillcreek.org/showthread.php?17615-Shameless-Festool-Sander-Plug) 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/Articles/ArticleViewPage/tabid/75/ArticleId/17/Grain-Filling-with-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/Articles/ArticleViewPage/tabid/75/ArticleId/17/Grain-Filling-with-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? :eek: 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.

[Chris Fournier]

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.



A six inch spatula that you can keep hot enough to grade shellac on a 4' X 8' surface? Do you have a video reference of this technique by chance? I am not saying that it's not possible but I am a sceptic having burned in a bit of shellac in my day.

[Jim Becker]

Sheldon, I don't disagree with you and can honestly state that shellac wouldn't be my own choice or recommendation for filling grain. Nonetheless, some folks will choose to do so for their own personal reasons.

[guy shiloh]

Anyone use Abranet sanding discs?

[sheldon pettit]

A six inch spatula that you can keep hot enough to grade shellac on a 4' X 8' surface? Do you have a video reference of this technique by chance? I am not saying that it's not possible but I am a sceptic having burned in a bit of shellac in my day.

LOL. you use a propane torch, not an oven or hot melt knife. Remember your not removing alot of excess since its already applied pretty uniformly not in a clump of shellac stick. All your doing is warming the 4-6-8" blade enough to pull excess of while packing the pores with what builds up on the knife as you move along. No.... there are no show you guides to do so but it would only take spraying a 1' board or so and testing yourself before moving onto bigger surfaces. Just make sure its a non flexible blade [thick type] and you heat it enough to do the job without burning the wood, just as you would do if burning in on bare wood with a lac stick ok? Again, the wood must be as flat as the blade to work properly, a wavy wood surface won't work!! I only used this method on flat surfaces.

[sheldon pettit]

Used them alot up till 06, found they were great for removing old finishes, didn't care for them as much for actually sanding the wood though. I prefer wet or dry for that. Last longer and sands faster, especially the heavier grits.

[Prashun Patel]

I use Abranet both on turned and flat work. It's good, but there are IMHO just as good 'conventional' sandpapers.

The screens won't corn up as easily, but they shouldn't be used wet.

[David Weaver]

One other side comment, to go along with the shellac being dry when you sand it.

You'll get a lot less plugging if you use the paper / sanding block only in one direction and lift it and repeat. The important part is probably just that you lift it and don't mash the paper back and forth over semi-sticky dust. I can't remember if I brush off the paper by hand at the end of each stroke, but I can scuff a large panel before having to deal with much plugging it.

If I just keep a block on a finish going back and forth, it loads almost immediately.

[Stew Hagerty]

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.
I have had good success wet sanding shellac using paraffin oil with either (or both) wet/dry paper or steel wool. After you get it cut back to where you want it, just wipe off the excess oil, then remove the remainder of the oil with a mineral spirits soaked rag. Then just continue with the top-coat of your choice.

Paraffin oil wet sanding is also a great technique for non french polished items. After wiping dry, apply a couple coats of a good paste wax and you have a great looking deep "hand rubbed" finish.

[Alan Lightstone]

I gave up on using shellac as grain filler. Just wound up being too much work. I'm much happier using oil-based filler (although I have a can of water based that I'm waiting to try.) It's just quicker and easier to fill the pores with. JMHO. Has other technique issues, but it works and looks nice when finished.

Still dying to try the plaster-of-paris approach, though.

I'll leave the big boys to argue about sanding the shellac. Learned something with the scraper approach, though Scott.

[guy shiloh]

Had to look up IMHO !I thought it was a brand of sandpaper.ha ha I love abranet ,they last a long time and don't fill up.I do use regular discs for finishing.

[Alex Borshov]

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.

Is this a good approach for Zinsser SealCoat? I'm not sure if this is quite the same as shellac. I used SealCoat to prep some birch ply for paint and the sand paper quickly plugged up, leaving gunk (corn?) stuck to the plywood that was difficult to remove.

[Prashun Patel]

Sealcoat is 1.5# dewaxed shellac. You can wetsand it with MS. Reading back thru this thread, I see that I'm in the minority in wetsanding shellac - so please don't go just by me. When I sand shellac - as a sealer - I sand about as 'aggressively' as when I'm rubbing out; I'm sanding for smoothness to touch. To this end, it's pretty quick. Each area really only requires a quick pass or three.

[Scott Holmes]

Actually Seal coat is a 2# cut 100% de-waxed shellac. The other Zinsser shellacs are 3# cuts. I don't know the cut of the spray can shellac; it too is 100% de-waxed.