I have used this twice on the same job, mixed with grout boost. First time applied it started it chip and flake out of joints! Cleaned all joints out full depth and removed all grout. Applied mixture that was mixed by strict mixing instructions and finished it out. Three days later grout flaking out again. I have done tile and stone work for almost 40 years and have NEVER had a job do this! I am really upset and will not use this product again! Stick with a known winner MAPI !! This is my first job with this product and will be my last!