PRODUCT: Buff 20Kg
If you do what it says on the tub - the tub does what it says. Make sure the surface and joints are completely dry. Ensure, as far as a forecast can be accurate, that the day you use the product is going to be dry. I used it just after 7am and left it to set for the rest of the day. It rained the following day - no breaking up or discolouration.
Make sure you have enough product for the area to be grouted, especially if the joints are deep like mine were. Work quickly as per the time constraints on the instructions.
Very happy with the result.