I'm currently installing a new bathroom with tiled shower walls. I chose HardiBacker CBU for my walls. I wanted to waterproof the HardiBacker prior to tile, and wanted to use Laticrete 9235, but could not find it in my area, so I used a waterproofing product called 'RedGard' from Custom Building Products sold at the big box. It went on alright, and seems to form a nice rubber membrane, but it did not seem to bond well to the Hardibacker. I can roll it off in big pieces. The RedGard was supposed to be compatible with cement board, but the manufacturers instructions did not specifically mention HardiBacker, so I called both Custom Building Products and Hardie, and they both said 'should be OK' without too much confidence. The good news is I've discovered the problem before placing tile. So, does anyone know what went wrong here? I did clean the surface with a damp sponge first. I'm going to rip off the CBU's and start over, and I guess I'll try the 9235 this time. Can anyone tell me of good experiences using 9235 over Hardibacker? Will the 9235 form a chemical bond with the hardibacker, or will it sit on the surface like a sheet, like the Redgard seems to. Does anyone know where to get Laticrete 9235 in Northern New Jersey?
Gary, yes it was to the tile side of the CBU. As I was cleaning up some of the dimples around the screw heads, I could pull up the RedGard around the screw, which is understandable, but in some areas the stuff just kept on coming off. I just didn't have confidence putting tile on top of it, when there seemed to be such a poor bond between the Hardibacker and the RedGard.