Grain fillers and their application

      A woodworker requests advice on applying grain filler to walnut. July 18, 2000

I have some new walnut I would like to finish so as to obtain a smooth, mirror-like surface.

I purchased a quart of J.E. Moser's Grain Filler from Woodworkers Supply hoping I could fill the open wood pores and apply a clear finish. I have repeatly applied this filler on a test sample of wood and fail to see any filling of the pores.

What might I be doing wrong? What might I do differently to fill the pores prior to applying finish?

O.K., I'm gonna assume that this is not a water-based filler, and provide advice based on using an oil-based filler. Are you going after a natural-finish walnut or are you staining it? Also, is this filler a thick paste? I would like to know these things, but I'll give you some advice anyway.

First, apply a washcoat of one part sealer to one part lacquer thinner. Spray one wet coat, let it dry, then sand with 220-grit sandpaper.

Now, be sure your filler is properly mixed. Take one part filler to one part naptha. Mix thoroughly, apply it wet (but not too wet) to the surface, in a circular motion. Spend a little time working it into the wood, but not too much; just until it gets somewhat pasty.

Next, start to remove the excess filler with a clean rag, using the same, circular application method. When the surface is almost clean, make a final pass, with the grain, to finish the clean-up of the filler.

Walnut has very deep pores. Let the panel dry a half a day or overnight, repeat the process, and let it dry just as long again. Then apply two to three wet coats sanding sealer to the panel, and let the coats flash off for about 10 to 15 minutes between coats. Let the sealer dry maybe half a day or overnight; again, you want it to be completely cured.

Now sand the surface level with either 220 or 280-grit stearated sandpaper; sand not just for smoothness, but take all the shine out of it. Then apply two to three wet coats of lacquer the same way you did the sealer, repeat the sanding process, then apply two to three more wet coats of lacquer. Let the finish cure two or three days, then wet-sand with 800 grit wet/dry paper, then 1000 grit wet/dry, then 1200 grit wet/dry. Buff with a good buffing compound, something not too aggressive, then finish it off with a final hand-rubbing compound or glaze.

You should then have that mirror finish you're looking for.

Now, if you are going after a clear natural finish, you may see some white or ashy-looking pores. This is from the filler and you may not like the look. It takes a lot of time and work to fill grain and get a mirror finish; I hope this is of some help.

That was a good, detailed reply. I would like to hear your comments on scraping the sealer rather than sanding it. I would scrape it, but many folks are not comfortable scraping a finish.

Yeah, I'm one of those guys not comfortable scraping it either! You stand a good chance causing nicks, and of dragging the finish off of the substrate, causing poor adhesion or finish failure.

I believe certain rules must be followed for a properly applied finish. Sanding is a must for any fine finish, and it starts with your white-wood sanding. Sand in progression. All too often, people will say, "I sand to a 150-grit finish before applying the finish." I ask, "How do you do that?" and they say, "Well, I start at 80 grit then go to 150 grit." That's wrong. You must start at 80, then go to 100, then 120, then 150. Any missed grits in between results in a poor sanding job.

From the original questioner:
I greatly appreciate your very comprehensive reply to my walnut wood-filling dilemma.

I am sorry, but I didn't explain my project very well. I am making racks for Mah Jong tiles. The walnut racks are about 2-3/8 by 1-1/16 by 18 inches, have a ledge on their front side for the tiles to lay horizontally and another ledge on the back that holds the tiles 26 degrees from vertical.

I would very much like to maintain as natural a finish as possible, as the walnut is very uniform in color. I mentioned the J.E. Moser's Grain Filler simply because that's what I have (I am open to using any other method of grain filling that you may suggest).

The J.E. Moser's Grain Filler is a transparent, water-based filler. They say it is made with extreamly fine silica, dispersed in a tough elastomer/acrylic/polymer resin. They say to apply it with a putty knife or squeegee, allow it to dry, and to sand with a non-stearated sandpaper.

The filler appears similar to wallpaper paste. I have repeated the application of this product as best I could, five times, following their instructions, and am unable to tell the difference between the area I treated and the area I left untreated.

I have experimented with water-based grain fillers. You've got to apply the water-based filler wet, and if it is fairly thick, cut it with a little water; just enough to allow it to flow down into the pores.

Roll it on with a paint roller then use the squeegee against the grain to remove excess material, which you should be able to reclaim.

You should be at a 150-grit finish, with a washcoat, before you apply the filler, like I mentioned above. One application should be all it takes, but you may need to repeat the process. Then finish to the schedule I mentioned above.

If this is overkill on what you are trying to do, cut out a coat or two on the schedule; i.e., instead of two or three coats do one or two wet coats. If the filler is good, this should work.

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