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Topic: Sub-base drainage, Right sub-base for sandstone slabs< Next Oldest | Next Newest >
JW1970
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Posted: 21 Oct. 2019,19:02 QUOTE

Hi all, Using Sandstone slabs to make a large patio. Working upwards we have MOT, then 75mm of mortar sub-base (approx. 8 sharp sand to 1 cement). Sandstone slabs are then laid on a 40mm full mortar base (approx. 6 sand to 1 cement). Mortar will be used as a grout. Slopes for drainage built into the sub-base and ACO drains at the lowest points. Should I be concerned that as the Sandstone slabs are porous and the sub-base is a sand and cement mix we may get water issues under the slabs? Thanks. John.

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Tony McC
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Posted: 22 Oct. 2019,12:39 QUOTE

I wouldn't be too worried about the sub-base drainage but I'd be very worried about that proposed build-up. It's a complete bollix!

75mm of mortar is NOT, I repeat, is not a sub-base. It's a layer of mortar. An unnecessarily thick layer of mortar, one that, at that depth, reaslly out to be a concrete , if it has to be there at all.

And then the plan is to top that with.....<drum roll>......40mm of yetrmore mortar!!! Why FFS?

The *correct* method for laying sandstone flags for a patio is shown on the main website


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