Lay flags onto tarmac

99rb99

Can anyone tell me how to lay flagstones onto tarmac.


The tarmac is in really good nic, no cracks, smooth overall surface, but it slopes slightly for drainage, so the flags would slope slightly too.


The flags are the smaller type, so pretty easy to handle.


Would I be ok to use just hard sand underneath them, or do I need to mess on with concrete?


Thanks :-)

Furts

I would be wary of laying over tarmac, but it is your choice. It is not something that a reputable contractor would do.

I would fully bed the slabs with 1:3 sharp sand/grit sand:cement mortar .

andrewf75

out of interest why would you not lay over tarmac? whats the difference between that and a compacted hardcore base?

DTDfanBoy

andrewf75 wrote: »

out of interest why would you not lay over tarmac? whats the difference between that and a compacted hardcore base?

A hardcore base is permeable, most tarmacs are not, if you have an incorrect bed it will be washed out over time.

Furts

DTDfanBoy wrote: »

A hardcore base is permeable, most tarmacs are not, if you have an incorrect bed it will be washed out over time.

Spot on, plus tarmac is flexible and slabs are not. Hence there may have been movement and the tarmac has flexed. This looks fine until one tries to lay slabs.

Add to this one does not know what sub base is under the tarmac. It could be absolute dross but the the tarmac will flex as it settles and moves. Not so with slabs!

Hence my comment about reputable contractors not doing OP's suggestion.