If your whole mask starts to dissolve/delaminate/distort before you washout your image for sandcarving, there could be a few reasons why this is happening. Underexposure or over-washing are most likely. Underexposure can be corrected by following the exposure schedule listed in your instruction guide. The underlying cause of over-washing is usually a lack of density in the artwork. This allows UV light to partially expose areas of film that should not be exposed. This increases the washout time. Increasing artwork density improves the results.
If the whole mask starts to dissolve, delaminate, or distort before you can washout the image, this is probably caused by lack of density in the artwork. A second possibility is that the mask has been exposed to UV light prior to use. This cannot be corrected.