Sub base or no sub base

[paulontour]

Hi

I have to lay about 30m2 of indian sandstone for a new patio. I am basically taking up an area that has concrete on it, smashing the concrete to pieces and then laying new paving.

Do I need to lay a sub base? Or will 80mm of sharp sand be enough? Has thought about laying on top of the concrete but may have an issue with the door.

Thanks!

 

[r896neo]

Its up to you but for the small amount of extra cost (although a decent bit of extra digging) just put in a sub-base 75-100mm will be plenty.

80mm is far too deep for a mortar bed it should be a maximum depth 50mm.

 

[paulontour]

Hi

Thanks for that.

Problem I have is that to put a sub base in would mean digging up the existing concrete. Am i likely to have problems if I dont? also, if i was to just cover the old concrete, what kind of mix do i need to lay the paving on?

 

[davemar]

I've got a similar situation where I've got an ugly old concrete patio, and my plan is to simply pave over it. I think the pavingexpert website give some advice on the best type of mortar for that situation.

How much extra height are you limited to?

 

[paulontour]

I'm limited to about 40mm near the door. But then it slopes down towards a gully in the middle of the patio. Was thinking I could lay the pavers nearest the door on a 20mm bed of sand, then increase it as I go towards the middle, sticking with the slope as much as possible (If i need a slope?)

 

[r896neo]

Hey, just wanted to check when you say a bed of 20mm sand you mean mortar, as in sand and cement?

Sandstone in particular needs to be layed on a full bed of moartar.

 

[paulontour]

Yes! Sorry, that is what I meant.

I think I could get away with laying mortar on the concrete and the slabs on top.

Any idea how much mortar I would need?

 

[r896neo]

use the calculators on paving expert