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I’ve been trying to get a clean, consistent finish on my latest woodworking project, but I keep getting tiny bubbles trapped in the polyurethane no matter how carefully I apply it. I’ve tried thinning it and using a foam brush, but the result still isn’t as glass-smooth as I’d hoped. Has anyone else run into this and figured out what they were doing wrong?

Yeah I chased that problem too. The finish on mine kept showing pinholes and micro bubbles. I switched to a single, thin coat of polyurethane and used a natural bristle brush, and kept the room steady at about 70F and low humidity. I still saw tiny bubbles but they were fewer and easier to sand out.

Foam brushes felt fast but I swear they introduced air each pass, especially when the can was a bit old. I started using a clean brush and slow, long strokes and the bubbles dropped a bit.

Are you sure the issue isn't dust or oil on the surface after sanding? A speck can turn into a bubble once the finish wets it.

I learned to let coats cure inside for a day or two and sand with 400 grit, wipe with a tack cloth, and then apply the next. But I still had tiny bubbles in the early coats.

I once tried thinning too much and the film ran instead of leveling, which pressed air into the surface. It looked smooth at first but the bubble pattern showed up as it dried.

Humidity and temperature were killers for me. Finishing in a damp morning meant the surface stayed tacky longer and trapped air.

I even toyed with a quick heat pop during the brush stroke, but I worried about scorching the wood or ruin the grain. Not sure if that helped or made it worse.

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