Warping 4 ply mount board

[ChrisG]

A number of frames with mounts completed a few months ago for same customer all hung in a dampish environment. One comes back with a wavy mount the only one with a 4 ply mount others were standard mounts. Replaced the 4 ply with a standard.

What is causing the 4 ply to warp? I may stop offering them especially as they are more expensive too.

[Not your average framer]

Mountboard is constructed with layers of paper and has the same directional characteristcs as imparted by the paper making process. When the paper is affected by dampness any distortion in the paper will reflect the directional characteristics of the paper used to manufacture the boards. It could be that the piece of board that you used was cut from the full size board the other ways round and used the direction of warp along the less helpful axis of the mount board.

It may be that the particular mount was hung in a slightly damper location, or maybe the were different hidden stresses in the four ply mount board, which reacted differently when subjected to the same dampness, or it may be non of these. I would suspect that there is no way of telling for sure, but a problem with just one mount, could just be a random happening and might not have anything related to the fact that it was a four ply mount board. I would not take it as a valid reason not to continue to use four ply mount board on the basis of just one incident.