I have a 1790 home that nothing and nowhere is true and plumb, but it is still standing. I have a double shower that has been tiled 3 times now and the grout continually breaks and then lifts. I am thinking my only alternative is to concrete the floor so that there are no weak points. I am also 6'7" and 285lbs. This is a second floor shower and all my carrying beams are logs. What type of cement or concrete would I use and how would I go about pouring it? And do you think that it would work? Thank you

I would rip out the old shower and maybe try to save the drain, you'd be the judge of that. This site will help you to build a proper shower pan from scratch. How to Build a Shower Pan

You could put a fiberglass shower unit right over the old tile. You could use waterproof tileboard and cut a hole for the drain. Mix 1 part Portland cement and 3 parts sand.

Hi, I'm sorry maybe I did not put down enough info. The tiled shower is only 3 years old and walls as well as floor are tiled, Only the floor tiles keep coming up. I assume due to an imperfection somewhere in the floor. Would/should I take up the tile floor and pour some form of concrete and use that as the floor since it would be 1 solid area.

Do you know what the shower pan is made from other than the tile and mortar it is set in/ Is there an actual shower pan built in place or aws the tile set onto a wooden floor?

Contractor had removed the tub and had level the floor they had then used a bladder, a rubber flooring cover that went down and then I believe they cemented over that and then tiled on that. A one piece hard floor had not been used.

Cemented over the membrane, about how thick is that cement? Here is how a real pan is built from scratch.How to Build a Shower Pan