Need advise on what base to build a patio on

[MartinSmith]

Hi,

Looking to build a patio area in the back garden, approx 18 feet by 12 ish. I've had conflicting advise on what and how the patio slabs should be laid.

Is it better to have solid concrete base, a dry mix balast base, or just to set them on sand? Also, how thick should the base be?

Any help would be appreciated.

 

[r896neo]

what are you laying?

And ignore all advice from whatever source told you a dry ballast mix is suitable.

 

[MartinSmith]

Thanks for the advice

Looking at laying fairly standard 18 square inch slabs. How thick should the balast base be? I just don't want the whole thing to sag and start breaking up over a period of time.

The ground is fairly solid, a clumpy soil clay mix, probably more clay tham soil.

Sorry, just read your message again, so you're saying that a balast mix is not suitable?

 

[Arthur2shedsJackson]

I have read that on clay you need a 4 to 6 inch base and I have always used this as a marker, but my soil is very heavy clay, which holds water.

Obviously the solid concrete base is going to be the best in the long run, but I have used a dry mix of sand cement and aggregate in the past, with the paving slabs then layed on a semi wet sand and cement mix and the slabs I laid using this method haven't moved in 7 years since I laid them.

As soon as the dry mix comes into contact with moisture ( from the ground or from rain it will set anyway. Perhaps the dry mix you should stay away from is a mix without cement in it ?

 

[big-all]

just keep it below 300mm above the highest natural point it covers and less than 50% off the garden area including extensions and other buildings to avoid needing planning permission

 

[r896neo]

I suppose the term ballast is what we are disagreed about.

Ballast to me is a pre mixed grit sand and clean stone mixture which is used to form concrete, it has no other purpose than for making concrete and will not compact because it is only sand and stone rather than MOT which is a full range from 10mm stone right down to dust, this mix of sizes make it compact well.

Back to the topic at hand. a 4 inch deep base of MOT is what you want as a sub-base or you can use a lean concrete mix which can be quite simply damp but really it shouldn't be totally dry.

As for laying it depends on the type of flags. as a general personal rule anything over 450mm or any type of natural stone i lay on a 5:1 sharp sand: Cement bed.

Block paving or concrete flags under 450 i lay on a compacted and screeded bed of grit sand around 40mm deep after screeding.