re-laying patio, subbase or not?

[andrewf75]

Hi,
Just had an extension built so the patio needs relaying. The ground seems pretty solid under the flags so is it worth digging it out to refill with hardcore or can I just level it off and compact it?

Cheers

 

[stef99]

I would never lay flags on top soil. they will always sink.

For a cheap sub-base you can use sharp sand, and a sprinkle of cement, but only for small areas.

anything more than 1-2m sq, I would advise on the sub-base.

 

[andrewf75]

I know you don't lay a patio on top soil, but the area I want to lay it already had a patio on it, so its effectively the old sub base not topsoil.

isn't it?

 

[r896neo]

dig a small hole and see what you have?

You need to at the very least lift the flags and remove the old bedding sand or mortar.

If the area is well settled then simply laying new flags on a good 6:1 mortar will suffice for a good few years. For a top job you'd want a 4'' compacted sub base.

If you already have a sub base then your good to re use, just get it to the right levels and recompact for good measure.

Any where that has been backfilled in trenches etc durgin building should be given special attention. capping them with 4'' of lean mix concrete for example

 

[andrewf75]

Great, thanks

what do you mean by capping the backfilled areas with lean mix concrete?

is that something different to filling them with hardcore?

 

[wrathkeg]

Yes, it is different. Lean mix concrete is gravel+sharp sand+cement at 6:3:1 (or all in ballast+cement at 9:1).

 

[r896neo]

back fill of trenches, especially deep ones like footings are often filled in with all manner of rubbish laying around site. even if they are filled with hardcore you can never compact it properly as its so narrow and deep. best thing is to fill them with clean rubble and cap them with concrete which will then span any gaps as it settles.