# polyurethane AND stain both sides or just poly?



## skogie1 (Sep 1, 2014)

Newbie question: I'm finishing a douglas fir table top and I'm wondering if I need to use both stain on poly on both sides to prevent cupping or can I skip the stain on the underside and just poly? Thanks in advance!


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## skogie1 (Sep 1, 2014)

that should have read "stain and poly on both sides" not "stain on poly…"


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## BLarge (Aug 29, 2011)

Oil based stain will not change the way, or rate the wood takes on or releases moisture… So oil based colorant on one side does not matter, I fact, why waste product!

As far as poly, oil based poly should not make your top cup. Oil will not be absorbed by the fibers in the wood, so theoretically you should get no expansion of one side over another. Now if you used a water based dye, or water based poly, you will most certainly see it cup, in fact, I am often shocked by how much it does… But, let that water completely dry on the side you applied, and that cup will resolve natural as the wood finds it's equilibrium.

IMHO, you don't need to finish both sides of a table top no matter what you use… However, there are some people who feel feel finishing both side with a finish that give you consistent water moisture absorption/ release will keep that top flat… If your worried, apply finish to both sides.

Good for you to tackle a project, the fun has just begun. Remember, no matter what you do to this project, it important you have fun and learn…


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## skogie1 (Sep 1, 2014)

Thanks! Speaking of learning… I lightly sanded the first coat of poly with 220 and it left scratches. What did I do wrong? I sanded the next coat with 320 but I still can see some of the scratches left by the 220. Thoughts?


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## BLarge (Aug 29, 2011)

Nothing, poly is a finish that melts into the last, scratches will be filled in by the next coat of wet poly. You should not be able to see the 220 scratches unless the are very deep…. Meaning the leave a depression in the next coat.

In fact, when rubbing out a table top I often start with 220 to hit the highest spots, the moving to 320 to completely flatten the top. Then, steel wool and lube to a satin sheen.

I would try 400 between poly coats, make sure it is really dry, remember, you are sanding only for a mechanical bond… In fact, I don't sand in between if it is less than 24 hours before each coat. Most manufacturers say sand if the surface has cured longer that a day, or if you have a bunch of air bubbles… Dust nibs, I just use a brown paper bad on the surface.


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## skogie1 (Sep 1, 2014)

Great advice. Thanks a lot.


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