patio question

[thedon009]

I'm having a patio put down in front of my garden outbuilding. My builder has put a layer of ballast on the soil, and says he will then screed over this and lay the slabs. Is the method viable?

Another option he has given, is that he lay some concrete down, then sand and slabs over this.

thanks for your time

 

[r896neo]

its always hard to give advise in this situation because terminology is very critical. When you say ballast do you mean ballast?

Ballast is a mix of clean 20mm stone and sand and is only used for making concrete. It is not suitable as a sub-base.

Sub-bases should be formed with compressible material with a mix of sizes. The usual for a project like this is MOT type 1 which is then compacted with a vibrating plate.

Paving does not need a concrete base and it is overkill. Alsof laying anything on sand over a concrete base is a terrible idea as water will not go through the impermeable concrete and it will waterlog the sand making it fluid.

Check out paving expert for comprehensive guide on the make up and laying of all manner of block and flag paving.

 

[thedon009]

thanks for your reply. Yes ballast is the ballast they use to make up concrete.
I have some ballast left over from the outbuilding job, so the builder said he could use this to make up the concrete for the sublayer for the patio. I know it would be overkill, but its going to go to waste otherwise.

I also have some screed left over. Could I use this instead of mortor to join the slabs to the concrete?

 

[r896neo]

By all means then use up the ballast. You could use a very lean mix if its just as a sub-base and will not be exposed. Something like 8:1.

Screed is mortar? is it pre-mixed in bags? Grit sand mortars are perfect for laying flags on just be sure to add a good drop of plasticiser to it.

Any flags at free edges will need either layed on building sand based mix or the same stuff as before but put some sbr in. As grit sand mortar does not grab well to flags.