Warp factor

QI was thinking of using millboard for new door cards. What thickness should I get?

Graham Sturley, Kettering

AMillboard really isn’t ideal. It’s basically a dense card with one face painted. It’s easy to work with, but even if the painted face is turned to the inside of the door it’s still likely to absorb moisture and warp. We’d advise using 4mm MDF or PVC foamboard as a base material instead.