I'm preparing to lay tile in my new bathroom and I picked up the cement board but when I got home I realized I bought quarter inch instead of half inch thick sheets. The Hardibacker website says that you can use quarter inch but a lot of websites that I've looked at recommends half inch for the walls. Has anybody use quarter inch cement board for shower walls with large tile with good results? another question I have is what is the preferred method for laying tile on concrete slab floor? Should I use cement board or the rubber mat uncoupling style? Any experiences are appreciated
1/4" hardibacker alone is an unsuitable substrate for shower wall tile. If it were attached to properly waterproofed drywall, plywood, or plaster it would be fine. Think about it, one wayward elbow, knee, or hip bump and you may get flexion which would cause the grout (or tile) to crack.
what is the preferred method for laying tile on concrete slab floor?
It depends on the application. Concrete is porous, so for water applications (like a shower floor) there are specific established methods for waterproofing, sloping, and draining.
For dry area applications, concrete is the perfect tile substrate as long as it is clean and dry. Just apply thinset mortar using the application technique recommended by the mortar (and/or tile) manufacturer.
If you're looking for the proper way to tile a shower, including pre-slope, pan, etc. take a look at this guy's YouTube channel. It made me realize that building a tile shower takes a little more than just throwing up some Hardibacker and tile.
I install 1/4" HB all the time right on top of 1/4" drywall. Easiest way to do a tub surround.