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That "experts" tip about sanding between coats of polyurethane cost me a weekend
A guy on YouTube said to sand with 320 grit between every coat of polyurethane for a smooth finish. I followed his advice on a maple desk I was building and ended up sanding through the first coat in spots after three coats. After the fourth coat I still had patchy, uneven areas and had to strip the whole thing down to bare wood. Next time I'll just apply a second coat without sanding if the first one's still fresh, like I've done for years. Has anyone else found that sanding between coats is overrated for water-based poly?
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the_oscar21d ago
Wait wait, are you using a sanding block or just the paper in your hand? Cause that makes a huge difference with water based poly. I learned that lesson the hard way too. You gotta use a soft block and barely let it touch the surface, like you're just petting the wood not trying to massage it. And yeah, if you're pushing at all you'll eat through that thin first coat in no time. I started using a foam sanding pad instead of paper and never had that burn through problem again.
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wesley_thompson21d ago
Oh I gotta push back on this one hard. You say you sanded through the first coat after three coats, but that tells me you were either pressing too hard or your 320 grit paper was actually more like 220. I've been using water based poly for years and sanding between coats is the only way to get that glass smooth finish without orange peel texture. Maple is a closed grain wood so you really gotta scuff it up or the next coat just sits on top instead of bonding. The trick is to barely touch the surface with the paper, just enough to knock off any dust nibs, and wipe with a tack cloth after. If you're sanding hard enough to burn through after three coats you're basically using the poly as a sanding sealer at that point. I've done entire kitchen tables where I did six thin coats with 320 grit between each and never had a single issue.
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Whoa, six coats? How long does that whole process take you start to finish?
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