This is news to me. Why would putting them in a
binder warp them? I can understand the very old
Vichy and Monte-Carlo material twisting after years
of breaking down...especially material made with
pyroxylin, camphor and laquers, or being in contact with
PVC... but the material used after WWII has stood up
very well both in lab tests and under most other
normal conditions involving heat and cold. I also
suggest tap
water never be used in cleaning any older pieces.

JB