Paving onto existing concrte base - Should i be worried?

[londongal]

My paving contractor is proposing to lay 5mm Marshalls Drivesett blocks on an inch of coarse sand (25mm?) onto the existing solid concrete driveway. The existing drains will be used for the run-off water from the top of the blocks but he is not adding additional draingae for the sand layer.

Having read the pages here on flexible and rigid construction and using an existing base and all the warnings about drainage, I am worried that we will have problems.

He has been paving for around 13 years and is on the Marshalls Register so I'd like to feel he knows what he's doing and don't feel confident/comfortable in challenging his approach.

Should I be concerned? Should I at least insist on this additional drainage?

Thanks for all the guidance so far. It is much appreciated.

[Rich H]

As the gaffer said on the other thread, the risk is that water becomes 'trapped' by the edging concrete at the sides and the concrete base below. With nowhere to go, the laying course of sand can become fluid leading to the formation of ruts in the drive. While you can combine rigid and flexible paving, due consideration needs to be given for drainage of the bedding.

[ambient]

everytime i have seen blockpaving laid over a concrete base it ruts where the car goes,
we used to do a lot of roads and cul de sacs which were already tarmacced some councils specified drainage under sand and some specified breaking holes in tarmac and some didnt bother,all had to be passed by highways