Foundation for patio slabs

[jlc]

Hi

I have a small back garden, mostly covered in patio slabs. A few have sunk a bit and become uneven and I want to level them off so my son doesn't trip on them. Is it OK just to put sand down or should I try sand and cement? Never done this before as you can probably guess!

John

[stoneyboy]

jlc,
Just use sharps sand, you can then re-level as needed.
end

[MickBee]

jlc,
Just use sharps sand, you can then re-level as needed.
end

The implication behind this advice is that if you only use sand, you will need to re-level from time to time.

On the other hand, if you want to do the job only once, an alternative way is to:
(1) make sure that the subsoil is firm (jump up & down on it)
(2) put down a bed of sand approx 1" / 25 cm thick, & level it to a depth below the slab-top of (25 cm + the slab thickness)
(3) put on a 25cm layer of sand & cement (for a small number of slabs, Lafarge Slablayer is simpler to use & not too much dearer.)
(4) Water the underside of the slab, and ideally coat it with Waterproof PVA adhesive
(5) Water the sand-cement mix thoroughly, and lay the slab.

When you have re-laid all the uneven slabs, don't forget to point between the slabs with a cement-mortar mix - for this too, it is better to prime the edges with Waterproof PVA adhesive.