Hi partners

I have a client with a 5 year old renovation. We did all the countertops. The builder screwed up the limestone floor. Big 12x36 tapered limestone tiles with radiant heat underneath.
Many of them came loose within the 1st few years. She hired another floor guy to fix it. He said the 1st floor guy used the wrong cement and he replaced with correct cement. I guess most of the tiles came up in one piece and he just re installed them.
Now she is having the same problem. Many are cracked and 1/4" grout lines are all cracking.
She will put the house on the market in May and just wants a quick fix.
I've heard of some tile installers using a glue or cement that will hold the tile in place so it doesn't vibrate and crack tile or grout.
I would like to fill some of the badly cracked tiles and also spot repair the grout.
Any thoughts on what I can use to inject alongside the tiles while they are still in place?
Thanks Chris
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