Regrouting with Epoxy
You can regrout with epoxy over cement grout, as long as you remove enough of the existing cement for the epoxy to adhere.
I recently completed a new shower stall in which I tiled the walls and ceiling with a combination of ceramic subway tiles and sanded grout. I sealed the grout with two coats of premium grout sealer, but after only a few months of daily use, the grout discoloration and frequent scrubbing are already becoming a headache. Is it possible to admit defeat and do a skim coat of epoxy grout over the top of the existing, sealed, sanded grout? If so, how do I prep the job?
It is possible to regrout using epoxy over cement, but first the existing cement grout needs to be dug out of the joints until it’s half the depth of the tile. This is most easily done with a grout saw or scraper. The idea is to provide enough depth for the new epoxy grout to adhere to the remaining sanded grout and also to the edges of the tile. Regarding the overhead installation, let the epoxy set up for a few minutes in the bucket after mixing so as to have a slightly stiffer, tackier mix.