Three days ago I stained an oak tabletop with a water based stain. I did not have time to apply the polycrylic till today. The tabletop has been lying flat in my garage. Today I go to finish the top with the polycrylic and the top is warped. Is there anyway I can get it flat without destroying the water base finish?  Humidity had been high in Upstate NY for 2 days then dropped significantly the last day or so. Top side of tabletop is concave so I’m guessing moisture difference between top and bottom is culprit. Any ideas how to unwarp a stained but not finished top?