Dear Peter,
I recently finished a dining table made of solid african mahogany. I planed and sanded the top to p220 grit, filled the grain, and finished with multiple coats of gloss varnish. I used a mixture of 4f pumice and linseed oil to fill the grain, rubbing the slurry vigorously over the surface and then wiped it off across the grain with dry rags. The final finish was rubbed out to satin sheen.
The table sat in my living room in Boulder, CO, for a month before being shipped to Albany, NY. No problems so far. After a month in Albany in an air conditioned house, white spots appeared. They were typically about 1/2 inch to an inch in size and were under the varnish finish. They appear to be primarily around the perimeter of the table, and the leaf showed no spots.
I have concluded that the spots are due to the grain filler, probably not completely removed after application. Do you agree? If so, what is the mechanism for forming the white spots? Is this process a good choice for grain filling in general?
Thanks for any help you can provide. Tom.
Replies
Tom,
There is nothing like having a long distance problem like this, I know.
First off, I would recommend using a good paste filler instead of the oil and pumice mixture. One I use is Sherwin Williams because unlike most others it contains silex which is ground quartz. It fills very well.
If I were to use pumice I would add some dry pigment like burnt or raw umber to it. This can be obtained from Woodworkers supply under the name Fresco powders. However I would only do this if I was using shellac as it dries quickly.
You said it sat in your house for a month before you shipped it. My question would be how long did you let the surface sit after filling the pores? I feel you put the finish on too soon.
Linseed oil does not dry by evaporation, it cures by oxidation. As you know this takes quite a while. Letting it sit for a minimum of a week in optimum weather and lots of sunlight would be a good choice.
I feel the oil is curing off and the uncolored solids(pumice) is now becoming evident.
If this is the case, and without having my eyes and hands on it for confirmation it's my best assessment, the only way to cure it is to refinish it.
Keep me posted on what happens.
Peter Gedrys
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