Laying slabs. 100mm of gravel and 30mm of sharp sand

[OldKettle]

Hi,
I am going to remove two raised beds which are located in a patio area. Patio area is level and approximately 10m x 5m and has half a dozen soakaways (not sure of the exact construction under the surface).

The beds are two bricks high and approximately 1.5m x 1.5m. They take up quite a bit of space, so I want to get rid of them. They are located on the right and left about 2m from the house.

I plan to just remove the bricks and soil to enable me to lay 100mm of 20mm gravel and then 30mm of sharp sand, with slabs salvaged from a path.

Does that sound sufficient as a base? Can I get away with 50mm of 20mm gravel instead?

Any thoughts would be much appreciated.

 

[Newboy]

The sand will wash into the gravel

Try here http://pavingexpert.com/layflag3.htm

 

[OldKettle]

Thanks. I read sharp sand on top of gravel (or MOT Type 1) elsewhere, and had assumed that it was advised as good for drainage. I had a quick look at the link you provided, but need to sit down and look through it properly tomorrow. I need to understand the drainage aspect better, and whether it is preferable for the bed to be permeable.

 

[^woody^]

The crucial thing is to have a reasonably firm base for the slabs, and that does not automatically mean needing hardcore.

As long as any "topsoil" type soil is removed, if the ground is then firm, then you can go straight on that with your sand, or build up with sand or sand and gravel as needed.

Gravel is not as good as a base as crushed stone (such as MOT) not because of drainage, but because round pebbles don't interlock, and can move under load - but in the case of a patio its largely irrelevant.

On the subject of drainage, you should be draining the patio via the surface levels, and so not much water gets through the surface (unless you are designing a permeable surface). So any sand wont wash away, but if you are using a more than 30mm of sand, you should ideally whack it to compact it, and then have another thin layer on to which you bed the slabs on.

To bed on sand, the slabs will need to be dead flat on the underside, else it's really difficult to lay then to any sort of level or fall.