Preparation for patio

[Jupiter01]

Hi,

I am planning to haave a slabbed patio area immediately outside my bifold doors. It's around 3.5 metres wide and 2.5 metres deep. It will be raised around 50cm from the ground and we have built the retaining wall out of blocks. It will then be cladded for aesthetics.

Q. Once the retaining wall is at the right height (around 20cm below DPC level), and in filled with hardcore and tapped down, what should I be doing next to prepare the surface for slabs?

Thanks in advance.

 

[jeds]

Just make sure it is well compacted. Don't try to compact the whole lot in one go - lay it in 100mm layers and compact each layer.

 

[Jupiter01]

perfect, once the hardcore is compacted, how do i prepare the surface above this before I lay the slabs on top?

 

[r896neo]

I did the exact same thing at my own home a couple of years ago and i would recommend building the wall and fill it with clean rubble. This way there is no need for major compaction as a fill that deep with type 1 MOT or similar will settle no matter how well you compact it down. Better to use clean rubble that has no compaction.

The issue with this however is that you need to lay your paving on mortar as sand would simply filter down through the rubble.

 

[Jupiter01]

Once I've compacted the hardcore, do I need to lay a membrane and how thick should the mortar be?

 

[r896neo]

No need for a membrane. Fill with clean rubble and then for the last few inches bring the size of the stone down to say 20mm clean to fill in the voids between the larger chunks. You then would need to lay on a good 50mm bed of mortar.

You could alternatively cap the whole lot with a few inches of lean mix concrete which would give a good tight flat surface to lay on.

 

[Jupiter01]

I was thinking membrane, to stop weed from penetrating through or is this not a risk?

 

[r896neo]

Not sure what weeds you think are going to grow through 500mm of rubble and a 50mm bed of mortar??

Aside from ground reinforcement geotextiles which are used under the sub base membranes have no place is domestic paving.

 

[Jupiter01]

I just know that the damn things come through anything!

 

[noseall]

It is largely a myth that weeds 'grow through' paved surfaces at all. Most weeds or growing material sets from above and into any surface. Gravel is most prone then block paving with all those joints. The seeds will find any gap or crevice and germinate.

It always makes me laugh when inexperienced landscapers make a big deal about putting weed barrier down before spreading gravel. Weeds love gravel especially the bits around the edges where there's zero traffic. all the fabric does is become an annoyance later on.

 

[Jupiter01]

Thanks @noseall. That sounds very plausible and I shouldn't need a membrane in my case.
However, can I challenge your point on gravel and the absence of a membrane as this is relevant for something else i am planning to do. I was planning to remove all the gravel I have in the drive at the moment as I want a different colour of gravel. I was then planning to lay a membrane a else the weed will grow through the earth and eventually my gravel. I appreciate that some weed may still grow within the gravel but presumbly the membrane would stop the majority coming through the ground?

 

[WabbitPoo]

try pavingexpert.com for all your answers (and ones for which you don't yet have a question!)


I have no connection with that site.

 

[r896neo]

You definately dont want a membrane under 50mm of gravel on a driveway. It will create a slip plane of sorts and cars may will spin wheels on it/skid the gravel over it and probably pull it up here and there. It will be a real pain.

 

[Jupiter01]

Thanks guys.
Back to the patio. Should I be using ballast and cement for this 50mm layer before the slabs?