I had two end-grain cutting boards that cupped about 1/16 inch after gluing. So one side is concave and the other side is convex.
If I let it sit, it stays the same.
If I plane it flat, then it cups again to 1/16 inch and stays there. But now is thinner.
I tried putting a wet towel on the 'in' side and then it flattens itself out in one day. But then it went back to cupped 1/16 inch again two days later. Any way to fix this?
(Editing to add images)
After two weeks the cupping did continue to get worst. The cup grew in size to nearly 1/8" and then stopped growing. I have waited for 2 months and the board has not cupped any more since then. Now I will flatten the board once again. I will report back in 1 to 2 weeks after this new flattening.