Fixing warped masonite? Then painting it?

[DollyKim]

My dollhouse is mostly masonite which has warped, anyone have any tips for flattening them out again? So far I've seen suggestions of getting them wet and putting a weight on them. Any idea how long I would need to weight them down?

One side of the boards is painted with a wipeable surface "paint" but I'm hoping to repaint them if that's possible.