Sub-base drainage - Right sub-base for sandstone slabs
-
JW1970
- Posts: 6
- Joined: Mon Oct 21, 2019 6:48 pm
- Location: Northamptonshire
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.
John W
-
Tony McC
- Site Admin
- Posts: 8346
- Joined: Mon Jul 05, 2004 7:27 pm
- Location: Warrington, People's Republic of South Lancashire
- Contact:
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
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
Site Agent - Pavingexpert