DIYbanter - Dimples in poly finish - Why? "poly 01 neg post.jpg" (1/1) yEnc 182284 Bytes

Greetings to the group.

I'm having a problem with 'dimples' appearing in my finish, and wondered what may be causing it.

I did two identical pieces at the same time. The problem only happened on one of the two pieces.

Conditions: Severe clear, 75 degrees outside, finished inside.
I'm brushing fresh oil-based poly over oil-based stain (major manufacturer for both). The first coat went on beautifully. I gave them a light sanding with 220 grit 24 hours later and removed the dust.

The second coat went on fine on the first piece, but on the second, the poly would draw back in some places - imagine a bubble in reverse, about 1/16 to 1/8 inch in diameter. I brushed it back smooth a couple of times, and each time it would draw away again at the same places. Parts of the piece look fine - the 'dimples' are only in some places, and often in clusters.

Sanded again, and the 'craters' remained very obvious in the dust. Note that there were no rims around the edges of the craters, before or after sanding. There are no dents in the wood.

I took a chance that I could get them to fill in using a 50/50 cut of poly. Better, but still there, and no dimples appeared in any other places.

The attached pictures show them fairly well, some better than others, and the negative versions give another idea of them. The forced flash at an angle is intentional, and some pictures had contrast and color adjusted. I got them as small as I could - the originals had better detail, but were 1 to 3 MB. Taken at about 1 foot with Sony Mavica 500

I've sanded back down to where the dimples are gone but a little of the first coat still shows, and will try another coat tomorrow.

I'm curious as to what problem may have been.

Ideas?