Abranet for Sanding Varnish and Shellac?

[Paul Carson]

Hello,

Is Mirka Abranet suitable for sanding between coats of varnish?

And separately, when Bob Flexner and others talk about brushing several coats of shellac and sanding them back instead of filling with pumice, is the sanding dust worked into the pores somehow afterwards with the tampon and more shellac, or is the action of sanding itself pushing abraded shellac into the pores?

Do you sweep the surface before applying the next coat?

In this instance would a regular sandpaper work better, as the Abranet excels at moving the abraded particles away from the surface?

Thanks, Paul

[Prashun Patel]

Dry sanding is not intended to fill the pores. It's intended to level the surface. the dust will be loose and will rub out or around when you put on the next coat. It is therefore best if you vaccuum the dry powder from the surface in most cases.

To fill the grain, you really need to wetsand the finish with varnish (instead of dry sanding). This will create a slurry that will stick better into the pores. When it dries, you can lightly level the surface by dry sanding, clean the dry dust off, then apply a new coat of varnish.

This works fine for mildly porous woods like walnut maybe even mahogany.

But for deep pored woods like oak a pore filler works quicker. After years of messing around with wet sanding, I finally learned how to apply waterbased pore fillers. Both Crystalac and Aquacoat work well. Wetsanding requires a lot of elbow grease. The pore filler does not. The only downside is that you need to let it dry (best about a day) and then sand it flat. Unlike the wetsanding, any residue on the top will show under a fine finish.

For leveling, abranet is very good. When used with a vaccuum, it will resist corning more than regular paper (in my experience). You will need 220 or 320 to level the above 2 pore fillers properly. However, I would also get some in 600 and 1000. These are wonderful for your leveling before your final varnish coat.

If you really want a flat surface, expect that any filler will shrink back into the pores over a period of a couple weeks after application. So, you may wish to delay your final couple coats for a week or two if you truly want a mirror finish. In this case, do your leveling just before applying the final coats.

Last, you should also look at AbraLON. These are padded abrasive polishing pads between 500 and 4000 grit. I have few in 2000,3000,4000. These are wonderful for 'rubbing' out the surface after your varnish has cured for a month (ymmv).

[Paul F Franklin]

I think when Flexner is talking about multiple coats of shellac, specifically, what is happening is that the successive coats of shellac eventually fill in small pores. The sanding between coats simply knocks down or mostly removes the shellac on the bulk surface, but not the pores, allowing subsequent coats to build up the pores until they are level with the bulk surface, giving a smooth result. In essence the shellac is acting as a pore filler, albeit a slow, and rather expensive one. If you do this with shellac it is probably not as critical to remove all the sanding dust since the next coat will redissolve any minor dust left behind. But with other varnishes, the sanding dust should be removed. I've used this technique with shellac on shallow pored woods and it works fine, but the other methods described so well by Prashun are more effective, faster, and less wasteful of finish.

[Andrew Seemann]

I tried the fill the-pores-with-shellac thing on the top of a white oak end table, probably after reading about it in Flexner's book as well. It took forever and a lot of shellac. Shellac was also the top coat. It looks very nice, wonderful clarity, but I haven't done it since. Too wasteful of time and shellac.

It seems to me I used a scraper for leveling rather than sandpaper, probably after reading about that technique in one of Frid's book. I also haven't done that since. It works, but sandpaper is simpler and more forgiving, especially with dyed or stained wood.

[roger wiegand]

In answer to the first question, I use Abranet all the time on both shellac and varnish between coats. It seems to work just fine. You do need to wait until the finish hardens to the point where it will powder when sanded; I expect that's the same for any sandpaper.

[Paul Carson]

Thanks very much for all of the replies. Really helpful.

Prashun, can you explain a little more about how you wet sand the finish? (Ignoring pore fillers for the moment) Do you do this with both shellac and varnish?

What do wet the surface with ? Can Abranet be used? Thanks

[Prashun Patel]

I don't wet sand shellac.

For varnish, it has to be thinned to a 'wiping' consistency as are ArmRSeal or Waterlox Original Sealer Finish or even Watco Danish Oil. If using poly, it would be the consistency of Minwax's Wipe On Poly.

I pour some in a shallow dish: Dip a shop towel in and wipe it on generously. Then use 320 or 400 grit sand paper to sand as best you can with the grain. When the varnish turns an opaque (ish) brown and gets a little thick, you know it has some sanding dust mixed in. You won't have gallons on the surface; you'll have teaspoons . You're looking for a little ribbons of paste. You can use a credit card to move that slurry across the grain like at 45 degrees - or even in little circles with the wrung out shop towel. You're trying to push that slurry into the grain. Wait a few hours until it dries. Then lightly sand with the same grit to make the surface smooth. I run my finger nail across the grain to try to feel if it's filled.

You may have to repeat this a couple times. If and when I did this, I would move up in grits each time: 400, 600, 1000, maybe even higher. I wasn't persnickety about packing the grain. I would just give the surface a quick once over after wet sanding to remove excess slurry from the surface. I wasn't aiming to fill the grain completely. If you like a satin surface, in-the-wood finish, this is fine (maybe even overkill).

If you want a mirror finish, then you can be more diligent about packing the grain. For your final few coats, you then wipe on the finish without sanding.

[Paul Carson]

Thanks for that Prashun.