I made a small box out of walnut, ash and cherry and used BLO followed by 3 coats of miniwax wipe-on urethane as a finish. When everything was dry I rubbed it out using mineral spirits and 600 grit black SC wet/dry paper. (On the back of the paper it says “Gatorgrit 600-b Waterproof Sandpaper.) After the mineral spirits dried, I was left with a very fine white powder that is deep inside the grain lines and I can’t get it out – tack cloths, vacuming, soap and water . . . ..all of this made a slight improvement, but the white powder is still visible.
Also, after rubbing out, the black sandpaper turns white and is presumably covered with the same white powder as in the wood grain.
I struggled with this before and thought it was because I had used a shellac washcoat, so did not use any shellac this time.
Any idea what’s causing this powder? Project looked great till the very last step . . . . .excuse the lousy photo; the white is much more visible than is showing in the photo.
BTW – THE WALNUT WAS RUBBED OUT FIRST TO AVOID GETTING ANY WHITE FROM THE ASH INTO THE WALNUT; I’VE SEEN THIS PROBLEM BEFORE ON WALNUT-ONLY PROJECTS.
Thanks
Mervyn
Replies
The white powder that has lodged only in the pores is likely just the "swarf" from the varnish . Usually mineral spirits or naphtha with a fine , not too stiff, brush should remove it.
The "easy" short cut for all walnut would be a dark tinted wax, though that wouldn't look so great on the ash unless you want to emphasize the pores. The wax would also increase the sheen, The 600 grit won't get you to a gloss finish, it should be a satin, a fairly matt satin I'd think. . But with only three wipe on coats of varnish you don't have much thickness to play with.
I don't "rub out" finishes,
I don't "rub out" finishes, but have a lot of experience with wipe on finishes. Along the lines of what Steve said, you may not have ANY finish on this, depending on the vigor with which you rubbed.
What is becoming lodged in the grain is the liqufied sanding dust caused by sanding the finish. The particles are very small due to the fine grit of the sandpaper. When the mineral spirits evaporates, the sanding dust hardens and dries in the depressions. It is almost impossible to remove them once the slurry hardens.
If you want to rub out a finish, you should be sure that the finish completely covers all the pores and depression. Normally, one would start with a grain filler to get a perfectly flat and completely filled surface. Then apply your clear coats followed by rubbing out.
Thanks to all. I did not realize the swarf would be so visible. Clearly its the walnut that's highlighting it - its the only wood that shows it up so badly and about the only dark wood I use.
I'll need to reevaluate my finishing, but at least now I know what's causing the problem!
Thanks
Mervyn
This forum post is now archived. Commenting has been disabled