This was posted on another site and may be helpful.
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If you've read the "Masonightmare" thread you understand my basing problems. If you haven't, the short of it was, "base is warped." This little trick can straighten a base that can't be fixed by pressing, usually because it has a building or something else glued to it.
1. Find something that won't warp that you can clamp your base to. Preferably portable, like a thick cutting board or an anvil.
2. Brush the bottom of the base until it's wet with plain water. Not horrendously soaked, but enough that it's clearly darker and if you left it to dry normally your base would be warped beyond repair.
3. If the object you are clamping your base to is porous (like wood), make sure that the area is covered with plastic or some other non-porous substance (glass, neutronium). This will make the moisture soak into the base, not the object you're clamping it to.
4. Clamp your warped, moistened piece onto the flat object. Make sure you clamp it flat; it will dry in this position.
5. Take the whole works and put it somewhere warm for at least 8 hours, but preferably over 24 hours. I used the top of the hot water heater. Don't loosen the clamps to peek. Once it's dry, the masonite will be completely flat. In my case, it was even flatter than it was when I bought it.
You can do a similar thing with masonite with nothing on it, of course, but it's usually easier just to moisten and leave it under a heavy object for a few days.
Read more:
http://gruntz15.proboards.com/thread/130#ixzz4MoPNGkZu
