Can I use a layer of Plywood in the walls with the Iso-Wall system?
It is OK to use plywood as the first layer of the IsoWall. Apply WallDamp as usual. We normally prefer using gypboard because the gyp is more heavy than plywood of the same thickness which allows the possibility for greater mass in a smaller space. But it can certainly be done using plywood. You can put gypboard over the plywood if you wish to make up for any lost weight.
