Flagstone laying technique - How to eliminate voids under flagstones

[flagstone_enthusiast]

Hello

I initially layed my patio with a screed bed using a dry sharp sand/cement mix last summer. Unfortunately, several of the flags rocked.

Having read the previous threads, I removed the loose flags and the bedding layer underneath. I replaced this with a moist 8:1 sharp sand/cement mix and used the surrounding flags as reference points to build up the corners of the new bed so that the flag was flush with the surrounding ones.

The problem that I have had is that several days on, although the flagstones are soundly in place, there is a noticable void when I tap on the centre of several of the larger flags (900 x 600mm). I imagine that they will eventually crack if not supported properly so plan on lifting and relaying them.

I would really appreciate any advice on the technique to lay these slabs so that the bedding layer provides good support across the flagstone.

I have some pictures of the patio and where the flags have been lifted that I can pass on, if needed.

Thanks very much

Simon

[lutonlagerlout]

sounds like you spot bedded them simon
you should remove and put in a fresh mix and without tamping leave around 10mm high,if your slabs are even say 38mm you could make a screed bar at 28mm
you then lay the slab on a full bed and tap down the last 10mm
using a rubber mallet
hope this helps
cheers LLL

[flagstone_enthusiast]

Thanks very much for the advice, LLL - I'll have a go this weekend.

Simon