We are designing a multi-level stone patio. To exit the kitchen directly onto the stone patio, the highest part of that patio would be 12 inches above the foundation. The next level would be flush with foundation, supported by a poured concrete slab (elevated with cinderblock, reinforced with rebar, filled with crushed gravel and another layer, etc.).
What is the best way to elevate the upper patio to meet the level of the exterior door?
One idea was to pour a slab to the level of the current foundation, create the necessary elevation from there, (16" center joists?), install cement board over joists, then lay stone or outdoor tile directly onto cement board. The area is not covered so the manufacturer warranty is less than when using for an indoor application. Any better ideas?
Has anyone used cement board outside on a floor (not wall) and had it hold up 10 years? 15 years?
(There was a question about this with an outdoor bbq about 4 years ago, but no update on final solution and results of that project.)
I don't know how to link to another question, but it was from Ronnie, titled
What cement board do I use for an outdoor bbq?
Best Answer
I would say the poured step, with proper expansion gap, however, PT lumber with the proper sub-floor/underlayment then backer board.
If you just use backer board, then tile/stone/etc, you will have the "floor" flex every time you walk on it. Crumble, crack, crumble, snap and you fall through. Water and backer board are not a good mix either. It is not concrete, but cement so it has no structural component. Backer board is the rough surface that allows the grout to adhere.
In other words, if you build a box step, use the same technic you would for an interior floor. Then seal it with a sealer to protect from water as best you can.