I expect we've all seen it ... a lovely terrain piece that is slightly spoiled by the base having warped after the texture, paint, grass, etc has been applied. I have a couple of such items in my collection. So I set about experimenting with ways to prevent it. This is what I've learned ... The base for the field (from my previous post ) ready to be pre-curved. Ideally I would not apply any texture first in case it fell off when the board is being curved, but in my enthusiasm to get it done, I forgot. Doh!? Approx size 26cm x 21cm, of 3mm MDF. Prop it carefully, upside-down , between two books. The edges just need to reach the books. I've found that for rectangular boards you should pre-curve along the longest dimension. Place a small, solid item in the middle of the board – it just helps to focus the force of the weight that goes on top. Now stack PLENTY of heavy books on top. MDF will take quite a bit of weight! This must have been in excess of 5Kg's. ...