Can I use soil under patio sub-base?

[Halitosis]

Hi, As part of a garden levelling project I wish to raise the height of a patio area approx. 400mm. Is it possible (or should I say wise?) to use soil dug from the higher part of my garden within the base of this - I'm thinking 200mm of soil which I would compact using a hired wacker plate, covered by 150mm of type 1 sub base laid over the top...
I would avoid throwing any turf in there, and maybe lay geofabric over it to avoid weed growth - is such a stable/solid enough base for a patio? (only foot traffic and garden furniture)

A supplementary question: I intend to use concrete blocks to build a short perimeter/retaining wall for this patio. Is it OK to lay the patio flags/slabs over the top of this wall (I am afraid that settlement inside the wall will cause sagging or breaking slabs)?
Thanks for any advice - I am an enthusiastic novice!

 

[r896neo]

Putting soil back in is a bad idea. You can use clean rubble as fill as long as its retained on all sides. Or use type 2.

Any settlement inside the block wall will just make the pointing crack and certainly won't break the flags.

 

[Halitosis]

Thanks for your reply r896neo. I wouldn't even consider it except for the fact it would save me around £500 in skips and buying the additional sub base
Is it due to settlement that would leave the patio uneven, or some other reason? It would be retained on all sides and compacted every couple of inches... definitely a no no?

Also would appreciate your advice on whether the slabs (I'm liking Tobermore Historic which are 50mm thick) should be laid on a dry or wet bed?
Thanks

 

[Andyc84]

Don't know what you are basing your £500 on skips from, but make sure you ring around the skip companies local to your area and ask if they do a soil only skip, down in the south west, you can get a 6 cube skip (builders skip) for £125 as soil and stone instead of the usual £250 for general waste...

Just a thought to try and save you a pound or two if you end up going this route...

 

[ladylola]

You could also put the soil on freecycle of maybe even e bay. When I dug some out on my own land I riddled the rubbish out of it and reused it elsewhere thus reducing the waste to get rid of.

 

[Halitosis]

Thanks both for good advice.
The cost is based on needing a fair few skips (and also bulk bags of sub base). The patio is going to be 75 sq metres

Before

• Halitosis
• 7 Oct 2014
• 5

 

[r896neo]

The tobermore historic flags are designed to be laid on a flexible unbound bed like block paving. In your case this is a big help.

I have laid them on mortar with a pointed mortar joint and on sand with a dry sand tight joint.

For a novice i would not recommend laying them on a mortar bed and trying to point them as its very hard to balance the joints and you can't open them up with a grinder because the flags have a preformed wavy edge.

Whathever you fill it with will settle a tiny bit so the best thing would probably to fill it with clean stone/rubble which does not compact and therefore will not settle. Then go over the top of this with a geotextile and maybe 4 inches of compacted sub base.

 

[Halitosis]

Thanks again r896neo. Without this forum I would be destined to waste a lot of money and time on a design doomed from the start

Last question on the subject if I may: why do you suggest clean stone/rubble - is it cheeper, superior, or quicker than simply putting down a lot more sub base and compacting it in layers?

 

[r896neo]

MOT type 1 is a graded hardcore containing all sizes down to dust.

The dust and small particle therefore compact together and form a dense rammed sub base, however clean stone or clean rubble has no graded material in it, its all large pieces.

As a result there is no compaction of it as its just stone trying to crush into other stone so there is nowhere to compact it into itself. As a result it doesn't settle and so is a good choice for deep fill applications as long as it is restrained on all sides.

The only compacting needed done is the initial layer to ram it well into the exsisting soil.

If you prefer to use type 1 get the heaviest vibrating plate you can or even better a vibrating roller

 

[Halitosis]

I understand - may require fewer bulk bags of the stuff.
Thanks again