QUESTIONHello, I will be replacing the spa spillway with a piece of granite. The current spillway is an unknown material, but I do not believe it is natural stone. I want to make sure I use the proper materials to seal and set the new spillway. I am assuming there will be a mortar bed under the existing spillway. I have tried searching for instructions on replacing a spillway with little results. Any guidance on prep and materials to use would be greatly appreciated. Thank you
ANSWERANSWER - I assume you will remove the existing spillway. Assuming it is bonded to a mortar bed or to the gunite/shotcrete substrate, after removing the existing spillway, make sure you scarify it and it readily absorbs moisture. Prepare the substrate for the granite installation. Make sure the substrate to which you are going to adhere the granite to has a 1/4" per foot slope away from the spa. Also make sure the front edge of the spill way is perfectly level so you get a uniform sheet of water flowing off of it.
If the rest of the spa hasn't been waterproofed then I would not waterproof the spill way substrate. I would bond the granite directly to the properly prepared substrate. Us a thin-set mortar adhesive that is suitable for submerged applications and that it meets ANSI A118.15 for maximum adhesion. Make sure you get substantially 100% thin-set adhesive contact between the back of the granite and its substrate. The joints around the granite should be at least 1/8" wide and filled with an ASTM C920 sealant suitable for submerged applications.