Recently finished a table top. Today moved it from my basement shop (43 % humidity and 70 F) to my home’s foyer (49 % / 74) and within 5 hours discovered several hundred pinhole sized bubbles had appeared. The bubbles were NOT present while the top was in my shop and finished for the last week or so. Bubbles are so small I didn’t see them at first but could feel them. Water-based finish, which was applied probably 4 weeks ago with no sign until today of these bubbles, so I have to think it was the change in temp and humidity.
Questions:
*is this very unusual? Has anyone experienced this phenomenon?
* what do I do now? Wait a couple days for more bubbles to appear, hopefully the last, then rub out the finish again? I need to deliver to an impatient client. I’m afraid I’m going to get a call a week after delivery because of new bubbles.
Thx for any ideas.
Replies
Detailed information on how you finished the table would be useful if you want a good answer. Also what was the wood species, oak or ash perhaps?
John W.
John,
Wood species is curly maple.
Aniline dyes first, water soluble. Then BLO. Then wash coats of shellac. Then multiple coats of Minwax Polycrylic. Rubbed out with Abralon pads and a festool ROS, then automotive polishing compound and finally swirl remover.
dan
What was the timeframe for all of this? Did you use dewaxed shellac? Are the bubbles at the surface, or deep within the finish? Do the bubbles really look like bubbles (roughly spherical), or more like flat, circular spots, as if you had some pinpoint delaminations?
-Steve
Steve,
yes, dewaxed shellac flakes (Behlen's). Pinpoint sized hemispherical bubbles, appear to be only at the very surface, though I'll find a loupe or mag glass to check further.
Dan
Well, I can only think of two possibilities: Either some solvent from the initial layers migrated to the surface, or else the bubbles were already there in some nascent state, but did not become apparent until later, either as a result of the change in venue (which doesn't really seem likely), or because the poly coats continued to shrink as they cured.
The boiled linseed oil shouldn't have contained any solvents, and unless you gave the shellac no time to dry at all, it seems implausible that there would be any significant amount of alcohol left in it. So that leaves the preexisting bubbles hypothesis. If that's the case, then another session of rubbing out should fix the problem.
You didn't say over what period of time you did all of the finishing. It's conceivable that you didn't wait long enough before your final rubbing out.
-Steve
I agree that it may be that there is too much finish of various types on the project. BLO takes 4-5 days to really cure to the point where it stops off-gasing. I've also had problems with waterborne acrylic finishes when too many coats are applied. Three coats is enough. And, while waterborne finish feels dry quickly, it still takes a couple of weeks to fully complete the coalescing and curing process. Rubbing out should wait for 3-4 weeks particularly if a power buffer is being used.Howie.........
I've never been a fan of waterbased products over a piece that at any time recently had oil based stuff. BLO, for instance, can take weeks or longer to fully cure.
Not that that's what's caused the problem. But it "could" be related to that.
One last comment. If anywhere in the vicinity, anyone had used a silicone spray like wd40 or something, those particles can stay in the air for hours, and if they land on a place where finishes are to be put, they can wreak havoc.
Good luck in your mystery.
That was my first reaction. Fisheye! I would think you would have seen fisheye very quickly. The incompatability of sovents seems to be the best suggestion. I have never been a fan of mixing oils and water but it seems like there was enough time to dry. You never know.
The curing of oils like BLO and tung can be confounding. I've had projects I let sit for a month and went to do a rubbout and discovered they weren't quite ready. Others, 7 or 10 days. Same shop and same conditions, within reason. Makes one wonder if the tiniest of change of conditions can make a big difference, or is it possible to get a batch of oil that for some reason acts differently???
Denny
Denny,
I know what John WW was getting at about the open grain species. I use precat lacquer on all my furniture, but I have had little pinholes on open grain woods (walnut, oak, elm) when I stained them or when it was very dry in my finishing room. Like you said, the oils in the stain must be uncured for what ever reason and migrate to the surface during the curing process. I always try to let stains dry overnight, but maybe on some occasions, that is not long enough. I use Mohawk wiping stains and they say they can be lacquered in 30 minutes, but I still try to wait overnight.
Well, I know how disheartening it is when this stuff happens. For me, I've tried two approaches to this outcome. One, get out the coarse sandpaper (or toluene), go to work, then restart the finishing process. Salvage may be possible. Or two, hang it from the rafters in the shop as a reminder of what NOT to do.
Good luck with it.
I like approach # 2.
I'm not bullsheeting either! I have a project (a thing I now make repeatedly) I screwed up royally on. What I did was take magic marker, and write all over the project with arrows and comments, the things I did wrong. I keep it in the shop. And everytime I go back to do another one of them, I look at it to remind myself.
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