I just figured out a technique that solved a major problem for me.

I had a large foamcore "masterboard" that had developed a distinct curve to it.

I flipped it over on its back on a flat, smooth surface (table), got a damp paper towel, rubbed the back of the foamcore sheet down with the damp towel, and placed a weight (large box full of stuff) on it.

Overnight, it dried and conformed to the proper, flat shape. It's fixed, and doing exactly what it's supposed to!

Sweet! Thanks Andorax... I needed this.

CCotD'

Hmmm, I seem to recall mentioning another similar method, once upon a time.

If the Masterboard warps when you glue the ground tiles to it you can often fix the problem by making it double sided, and weigting as mentioned above.

I don't use that technique much, my builds tend to be either permanent or modular, but it is the way I did the masterboards for the Mordheim campaign I used to run. It worked fairly well.

The Auld Grump