Why is some cement board rated for walls but others are not?

Which brand are you referring to? We use 1/4" on floors and 1/2' on wall generally because of the rigidity required for the application. A floor will not deflect because it sits on a 3/4" sub, walls can deflect if not 1/2"

That's not the reason for using 1/4 on floors and 1/2 on walls. You can use either on floors, but you shouldn't even think of using 1/4 on walls. Use 1/2" on walls mainly because that is the thickness of wallboard that it often has to transition to.

Jaz

Jazman is rite

adarric, I don't think anyone has been able to answer your actual qusetion yet because we still need to hear from you. Where do you see a rating for the cement board you want to buy? Form follows function, so a great deal depends on your application. Most cement board on walls will be covered with tile. Thickness of 1/2" cementboard, thinset and tile can approach 3/4" or more, so you would need to decide how you want to transition to another surface, if any.

ballengerb1,

You said;

"Thickness of 1/2" cementboard, thinset and tile can approach 3/4" or more, so you would need to decide how you want to transition to another surface, if any."

What the heck are you talking about?:eek:

Jaz

Jazman, you brought up the issue of transition in post #3. Have you tried to answer the primary question asked by Adarric? That is what we are here for.

Which brand are you referring to? We use 1/4" on floors and 1/2' on wall generally because of the rigidity required for the application. A floor will not deflect because it sits on a 3/4" sub, walls can deflect if not 1/2"

Actually, when Hardi first came out, it was 1/4" only and they sold 1 1/2" strips for furring out the walls to join up with sheet rock. 1/2" cement board makes it easier to join up with 1/2" rock.

I really don't understand the question about how to transition between the tile and another surface...

Bullnose, rondec, surface cap tile, mud cap, moldings, etc, never been a question for as long as tile has been installed.

The only reason, besides the need for meeting up with another wall surface (such as sheetrock) would be the flextural strength of the board. If you were going for an old floated wall look without floating the walls or furring out the walls, you could actually top off 1/2" with 1/4" and then use mud cap to transition the wall tile back to the existing wall. I've use 1/4" on the wall many times to transition glass tile with stone to bring them all to the same plane.