Am i using the right sub base for my raised patio? - Sub base

[mathew_temple@yahoo.co.uk]

I'm in the process of constructing a raised patio immediately outside the back of my house. The garden has a slight down hill slope running away from the house. The patio will be 8m a cross and will extend out 4m I have built a retaining wall around the edge and have now reached the stage where I need to fill the area with infil to bring it up to desired height (150mm below the house damp course). Where the slope is at it's maximum I will need to raise the ground level approx 800mm. I have just had delivered 10 tonnes of sub base material which is a dusty red in colour and has small limestone particles (approx max 35mm in diam). I was proposing to wheel barrow this into place and then compact it down. Will this type of sub base be sufficient to guard against the possibility of the patio paving slabs (concrete precast millstone flags) sinking in future or should I use another form of sub base. My concern is that the sub base material appears quite fine and someone suggested I should have used a cleaner 'chunky' hardcore to begin with and finished with the finer sub base before laying the slabs on a concrete bed. Will I be ok laying 250mm of the finer sub base at a time and then compacting and building up the height in this fashion?

[Nigel Walker]

The sub base material sounds ok. I would suggest laying it in 150mm layers and giving it a good compaction with a Vibrating Plate (wacker plate)
You wont have a problem, as long as your retaining wall is of sound construction.


Nigel