When you use Marine Grade Plywood in the Kitchen or Bathroom in the house that they are the most likely to be subjected to water moisture and damage. The kitchen floor and walls get spilled on and splashed; the bathroom contains a shower, toilet and bathtub that can create other problematic water issues.
Uses of Plywood
Filling Knot Holes in Plywood
With marine grade plywood under the walls and as the sub floor in these rooms will help avoid the wood from warping or rotting. Remember that Marine grade plywood is not suitable for any project in which compound curves are involved, since plywood does not bend in two directions at once. When it is not properly sealed with varnish, paint or other coatings, even marine grade plywood will eventually rot if left exposed to the weather.
Problems with Regular Plywood for Bathroom Projects
Sometimes the problem with plywood is simple The glue they used has become old so in the heat of being in the loft after all those years it has become plyable wich inturn allowed the Humdity in the air get inside of it and caused it to curl up going to the dryer side of the board so you see even if you store it it will still curl. Make sure you use a plywood that has been graded by the APA and meets your water resistance needs.