Red Guard Shower Pan
You can cover your mortar pan with it but it is not intended to waterproof the pan.
Red guard shower pan. Take half of a one gallon pail of redgard and spread it over 40 square feet for the first coat. You would have to research how to install a mortar pan but they are best done by skilled tradesman. Then take the remaining half gallon and apply it as a second coat.
Use two thicker coats to create a waterproof shower pan liner meeting iapmo standards. If using a roller apply a continuous even coat with overlapping strokes. Red guard or similar waterproofing goes over your walls.
Redgard waterproofing and crack prevention membrane prevents cracks in tile and stone floors due to surface movement. The membrane also produces a moisture barrier. Redgard has tested and complies with uniform plumbing code and international plumbing code standards for use as a shower pan liner per iapmo research and testing inc file no.
The pan is over concrete flooring with a linear drain installed. Suitable for use in residential and commercial tile and stone installations.