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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?

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  • Not sure how to link. Previous question was asked by Ronnie on Aug 1 2013 at 4:51 Title was What cement board can I use for an outdoor bbq.
    – Taki
    Mar 18 '18 at 22:06
  • Don't know how to link. Original post was titled What cement board can I use for an outdoor bbq. Only keyword was cement-board. Post was from Ronnie, Aug 1, 2013
    – Taki
    Mar 18 '18 at 22:12
  • I'd personally want a fully poured concrete raised step. What if water gets inside your raised box and starts to rot that wood- unsafe steps?
    – Chris Paveglio
    Mar 18 '18 at 23:56
  • Contractor said it's unwise to butt fully poured concrete slab up against the house even though the siding is Hardiplank. We're hoping for other options- the idea of the 'box' (or fake deck on top of the slab) was the only one we could think of. Concrete slab at the level of the foundation would have a small grade to prevent water accumulation on raised patio. That change in grade would be under the part that is built up with joists to be the step. Is the grade change in the slab plus some drains on top of new step, be enough to keep things dry?
    – Taki
    Mar 19 '18 at 0:19
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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.

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