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I am finishing an oak table. I lightly sanded the polyurethane after the first coat, as per the instructions. After the second coat of polyurethane dried, I see sanding/brush marks. If I don't sand again, will the third coat of polyurethane cover these sanding/brush marks?

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I would sand this coat with a much finer grit of sandpaper than you used on the last coat. Then wipe it down with some alcohol before applying the next coat. This will help remove the deeper marks and the sanding dust. Also, use a foam roller or foam brush instead of a bristled one.

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  • Will it still show if I put another coat of polyurethane over it as it is now? I am afraid to sand too much and ruin the stain underneath! – user98358 Mar 10 at 20:23
  • Using a finer grit will only knock the top off the grooves and allow for a smoother next coat. There is no way you will get down to the stain unless you use an electric sander. Use a 220 grit sandpaper. – Jerry_Contrary Mar 10 at 20:43
  • Thank you! I used 220. I think I will get something finer. – user98358 Mar 10 at 22:14
  • So that means it would show through if I just polyurethane without this sanding? – user98358 Mar 10 at 22:47
  • If you just go over it with a coat of Poly, it will most likely still show up. You can switch to a 320-400 grit sandpaper for an extra fine finish. The marks left behind are merely tiny ripples. You want to sand them to try to smooth out the finish. You aren't harming the finish at all. You are strengthening the next coat by allowing it to adhere better. Using that poly brush will help a great deal as well. – Jerry_Contrary Mar 11 at 11:26

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