On Monday, November 12, 2012 1:55:08 PM UTC-8, wrote:
We are putting a 41" X 33" mirror in the tv hole above our fire place. The Mirror is 1/4" thick. The TV hole is standard framing 2x4 with header. The mirror would fit into the hole in the existing framing with the trim that was applied for the TV hole. The plan was to put a 1/2 inch sheet of plywood as a backer board for the mirror. The mirror and the backer board would be held against 1X2 frame attached to the trim of the existing TV hole. Today I went to get the wood to cut the 41X33 backer board from. I realized that even 3/4 plywood will warp not a good thing if the mirror is masticed to it. What would you recomend for a backer board? I have talked to several people with ideas all over the board. from sheet rock to no backer.

MDF