Brief Information on Waterproofing a Shower Niche
To waterproof an inset shower niche, first apply a layer of stucco mortar. The stucco mortar should be applied in a grade that approximates the desired finished grade of the shower niche. Allow it to dry thoroughly. Then apply several layers of tar paper to the shower niche, beginning at the corners. Apply it to the seams as well. Then you should apply the tar paper to the base. There should be at least 3 layers of tar paper when you have completed this step. Then apply a layer of thinset mortar to the desired grade. Once the layer of thinset dries, you can begin the tile installation.