Block paving on semi-hard base

[Novice]

I need some advice please.

I decided to ask a family friend who is very good at DIY to help me build a block paving driveway and path. I am a complete novice at most DIY projects, but I did take the time to do some research. My understanding is that a driveway should be made up in 3 basic layers. MOT type I (approx 100mm), sharp sand which is split into 2 layers, approx 35mm compacted, and a 15mm screeded layer, and the final layer is the block paving. I explained this to our friend, but he has gone on to make the driveway using the following layers. Bottom layer is MOT type I (100mm). Middle layer is a mix of sharp sand (5parts) to cement (1part) plus a bit of water, ie semi dry this is the evening out layer so ranges in thickness from say 50mm up to 100mm. Final layer, block paving. His reason for using cement is that he cannot see how sand will stop the paving from sinking. My view is that if the edges are firmly bound in and the MOT layer is firm, the block paving has nowhere to go. I'm worried that the cement which creates a semi hard layer, will start to crack under weight or due to changing weather conditions (I live in London). Am I justified in being concered, or has what our friend done likely to work?

Many thanks

[84-1093879891]

What you mate has done is a classix illustration of the adage that "A little knowledge can be a dangerous thing".

We do not use a cement-bound bedding layer beneath flexible block paving. The clue is in the title.... FLEXIBLE block paving. His method is a sort of halfway between flexible and rigid but doesn't meet the spec for either, to be honest.

Just how this botch will perform over the longer term I can't say, but I wouldn't be too optimistic. It probably will crack, but how that will affect the appearance of the blocks, I can't predict without seeing the job itself. I'm guessing you'll experience a degree of channelisation (rutting) and you may well find that some areas of the paving start to experience a greater degree of efflorescence.

I'm not sure that it's worth ripping it up and starting again, but I certainly wouldn't be buying a pint for that partiucular mate the next time I see him!

[Novice]

Not what I wanted to hear, but many thanks for the reply.

[suki]

3 layers =150mm minimal (6inch compacted class 1 MOT) ,25mm-50mm screeded sharp sand ,and a block that needs to be passed with a wacker plate a good few times to consiladate blocks into the sharp with a cusion of kiln to protect the blocks from the vib plate