Not sure where this problem is coming from... I have two 1/2" layers of MDF (1200x1200mm) that I have screwed together and leveled. I shellac the leveled area so that my spray adhesive has better grip than raw MDF. Within 24 hours, different locations within a 24x24" area can vary by a whole millimeter. I'm cutting .025 aluminum sheet. So, that much variation is a problem. Is MDF easily effected by humidity change? Suggestions sincerely appreciated.