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I just stripped, sanded, stained & then applied fast-drying oil-based polyurethane to my hardwood table. All went well until I sanded the second coat of polyurethane with 220 grit sandpaper. The scratches did not cover with the third coat & streaks are visible.

Should I sand well now with 220 grit sandpaper & apply another couple coats of poly? I hope I don't have to strip it again!

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You shouldn't need to strip unless you scratched through to wood.

The problem with polyurethanes is that they are hard films that don't blend with the previous coat. Other finishes will 'melt into" the previous one (lacquer, shellac, tung oil)

Your sanding, @220, was too aggressive. Intercoat sands should be at 320 - 400.

You will have to sand back to a common level that eliminates the scratches and lines. If you leave part of one coat and part of another coat, there will be a "witness line" . You can wipe down the area after sanding with a soft-mineral spirits cloth and look for the lines.

Be sure you are allowing enough time between coats with the poly.

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I think too that it wasn't a long enough drying time as I sanded after 6 hours & it didn't feel quite dry. Are you saying I should sand it all away without disturbing the stain. What do you mean by "witness line"? I think I know what you mean but not sure. Thanks alot for your in-put! It is only when the light reflects off it that it's obvious but the streaks are not down through to the wood. –  Gloria May 16 '13 at 21:31
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I'm saying to sand out scratches and streaks, and try to leave the first coat. It may not be possible. Clear finishes are tough. Polyurethane is not a beginners finish.. You may want to try spraying the last coat or 2 with aerosol cans. –  HerrBag May 16 '13 at 22:28
    
Thanks again! Should I use the 320 or 400 grit by hand, sanding block or electric palm sander? –  Gloria May 17 '13 at 10:48
    
All finish sanding would be best with a block, keeping it in full contact. This will prevent breaking corners and localized sandthrough. I only use hand and electric sanders in the raw wood phase. –  HerrBag May 17 '13 at 12:06
    
Sanded with 320 & then 400 grit sandpaper on a block. Wiped it down with soft cloth dampened with varsol & did another coat of poly. Sanded the second time once dried for several days, wiped with varsol cloth again & recoated. Turned out great, no streaks. Thanks again HerrBag! –  Gloria May 27 '13 at 16:08
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