Granite slabs lifting - 450x450 slabs lifting

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Chaps,

Thanks for your help in advance......

We have just had a new patio laid - split level. The ground level seems fine and i can't lift the slabs up, on the raised level the slabs are now lifting.

Sub base is type 1 then a 50mm (4:1) silica sand/white concrete bed with the slabs laid on. No SBR was used which in hindsight maybe should have happened. Fortunately we hadn't put the jointing mortar in so the slabs can be taken up relatively easily.

What do i need to tell the contractor to do. Could i put perhaps a new 20mm bed on with SBR on the slabs. Or is there an adhesive i could use, the bed seems fine.

Any ideas would be greatly appreciated.

Thanks
Adam

[lutonlagerlout]

did your fella use a wettish mix?
seems strange that 1 half is stuck and 1 isnt?
LLL

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Seemed quite wet, similar consistency to the mix for bricklaying and they did have plas in the mix

I'll have another look at the other part and see if any can be lifted.

[sy76uk]

Was there any traffic over the slabs before the bed had a proper chance to cure? I try and stay off them for at least 2 days and even then only go back on them to point up.

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No traffic over them for 2 maybe 3 days

[lutonlagerlout]

one thing that worries me is this comment

i can't lift the slabs up

why would you even be trying this Adrian?
as long as the slabs/flags didnt rock or move there is no need to apply a vertical force to them
20mm bed is no good
all the bedding must come out and be redone
LLL

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How this started was my 5 year old noticed a rocking slab and when I gently pulled it it the slab lifted

I tried to lift some others (gently) on the lower level and they did not move so I am assuming they are set.

The slabs that have moved have a 30mm lip over the wall so I am assuming that it the problem. As far as i can tell the rest of the patio is ok.

Could I just remove the bed from the affected area and relay a new bed 4:1 mix as before but with SBR added?
Do you have to put the SBR mix on the back of the slab as well or is it ok just to add to the bedding mix.
How much SBR do I need to advise to put in the mix.

Thanks for your help on this it is very much appreciated!

[lutonlagerlout]

when a slab runs over a wall we normally use bricklaying mortar with SBR on the leading edge
because of different drying times from type 1 to brickwork this is a potential weak point
LLL

[ADS]

Could I fix the slabs down to the bed with Sikadur 31 2 part epoxy - looks like it should work.

The bed is very solid and the rest of the patio seems ok - no rocking or wobbling.

[ADS]

Right I'm going to go for it with the Sikadur 31. Breaking the bed up will cause to much damage and unsettle the other tiles - none have moved in the weeks afterwards.

[dig dug dan]

It amazes me why people insist on trying to pull up slabs like this, then try to correct it themselves.
have you not contacted the installer?