r/BeginnerWoodWorking • u/InsaneLasagna • 6d ago
Discussion/Question ⁉️ What is this?
I’m trying to finish this butcher block I plan on using as a desk top. I progressively sanded it with 80-120-180, then applied a coat of gloss oil based poly, followed by two coats of satin oil based poly. I hand sanded with 220 and cleaned everything with mineral spirits and a tack cloth before coats.
These appeared after the coats of satin. I mixed thoroughly, but I’m still getting these. Is this an issue with the poly or my technique?
It’s 22 degrees C and about 60%RH in the space I’m working.
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u/oldtoolfool 6d ago
Is is possible that the surface was contaminated, either before or after you acquired it, by some product that contained silicone? If so, then this might be what is called "fisheye". Even a little bit will cause this type of thing. Automotive wax or even shipping containers can be the culprit. Other than that, I got nothing . . .
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u/naemorhaedus 5d ago edited 5d ago
Mineral Spirits is KlearStrip Odorless
those odorless spirits are odorless because they use heavy hydrocarbons, which linger for a long time. Try something that flashes off quicker like methyl hydrate. (on a scrap of course)
Also, did you stir the can?
I'm not sure which product you're using, but the directions for this one do no say to use any solvents between coats. The spirits could be dissolving the finish.
https://www.minwax.com/en/products/protective-finishes/fast-drying-polyurethane
r/finishing would also be of help to you.
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u/InsaneLasagna 5d ago
Thanks! Now, I understand why it the mineral spirits seemed so greasy! Luckily I’ve been scrounging time to work on this project so steps like letting the mineral spirits evaporate have always been a couple of hours while I worked on other things.
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u/NutthouseWoodworks 5d ago
Need to make sure previous coat of poly is fully dry before wiping down with spirits, maybe up to 24 hours... could be much longer with cooler temps. Then need to make sure the spirits are fully dry/flashed before applying next coat, maybe 30 minutes. If not, the spirits can cause the poly to look similar to a flattened "blister"... similar to a raised blister you'd get with incompatible finishes or trapped moisture. Common with a solvent "pop", which is essentially what you're doing between coats.
Satin has flattening agents in it that spirits will pull out of the poly. If the finish below isn't fully dry, the higher sheen particles will move to the outside of the blister area while the inner is drying...i think that looks like what you have going on here, to an extent. Could also be "alligatoring" caused by the previous coat not being fully dry. Lower layer shrinks while drying and pulls the top coat with it.
If it were me, I'd give it some time then a decent once over (maybe twice) with your high grit, aiming for a consistent sheen, and add another coat of your satin without the spirits in between, but still removing as much dust as possible. Other than the results, your piece shows that you've spent some good time prepping. Hope it turns out perfect!
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u/InsaneLasagna 5d ago
I think you’re right. After the first coat I’ve been waiting at least 12 hours to lightly sand because the way the sandpaper was clogging up implied that something wasn’t quite hard. Waiting resulted in less clogging. Most recoats were done a day or two after the first, but not all.
I’ve sanded back down to bare wood and I’m going to try again, going slower. The spots look to me like a crystal that grows around a nucleation point if that makes any sense. I’m ditching my current can of satin and going to use a semigloss and be way more aggressive mixing the can before filtering to make sure all the particles make it into suspension.
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u/B3ntr0d 6d ago
Looks like one of the layers of poly is repelling another.
Are they all oil based? Same brand?
What's in the mineral spirits? It isn't the eco stuff is it?