Laying slabs on dry sand/cement

[baron777]

hi,
I have recently asked a landscaping friend of mine to lay some paving slabs to provide a driveway, .
what we did was first dug out the area 8 inches deep, then filled it with 4 inches of hardcore, which was then compacted down with a whacker plate, to provide a solid sub base, he then dry mixed sharp sand with cement (approx. 1:10 ratio), and laid the slabs on this, is this ok, or does the mix have to be a wet mix?
what we did was lay 2 rows of slabs then a row of gravel, then another 2 rows of slabs athen another row of gravel then another 2 rows of slabs, and edging stone at the end.

this looked great until about 24 hours after it was finished somebody came to the house and parked on it, and one of the slabs moved,
I don't think he whickered the sand down, and the other slabs seem ok. and the pointing was also done using the dry mix.

but because its being used as a driveway, my main worry is will it last if the slabs have be laid on a dry mix of sand and cement?

thanks for reading,
colin

[Tony McC]

It would have been better to use a moist or wet mix with this project, because of those central gravel strips. A wetter mix would have provided greater adhesion and so prevented the lateral slippage into the unbound gravel, which is offering buggerall in the way of restraint.

The only effective fix is a lift and re-lay. You might be able to re-seat the flags onto the existing bed using a thin wet bed of slurry mortar with added SBR as a bond bridge, but where you meet the garage, public highway or any DPC, it's probably necessary to break out the old bed and put in new.

[baron777]

so do you think it I left it and did nothing, I would get problems later on?
or would it be an idea to make a small trench along each row of slabs and fill it with concrete, so that they slabs don't move, but not right to the top of the slabs so that its showing, would that support them better?

there are 40 slabs so I don't really want to get them all up and reset them.

thanks