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I have no experience with water based poly so forgive my ignorance. I decided to try it on a project and really like the drying time and how quick it lays out on the surface. The problem came after 4 coats. I wanted to smooth out some spots so i went to lightly sand with 220 and immediately went right through the stain and all. It had sat for about 30 hours or so. So the only thing I can think of is that the coats are really thin or it didn't cure long enough. I brushed it on because i couldn't get an acceptable spray with my equipment.

Any thoughts?
My experience with water based poly is it takes 4 coats to equal 1 of other finishes so you probably just didn't have enough. When you do sand you have to be careful just how much you sand. It would have been better to just very lightly scuff over it with 320 grit paper after each coat then to put 4 coats on and then try more agressive sanding.

From where you are the easiest fix would be to chemically strip the entire area where you sanded through the finish. It's more work and takes much more skill to try to touch it up then to strip. When you are applying the finish it's more important to give it a good drying time between coats then to wait 30 hours before sanding. Just go by the label instructions and give it much more time if the weather is especially humid or in winter close to 50 degrees.

You should have been able to spray the finish. It sounds like the sprayer needs a thorough cleaning. From time to time you have to completely take them apart clean them. What kind of sprayer do you have?
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