How much cement for my patio?

[Rhbeen]

Hi,
Im laying an approx 15 sqm patio in my garden and I have a few questions:

1. I have put approx 7cm hardore into the hole I dug which is approx 20cm deep, but it doesnt seem to be level and sloping away from the house. Will this be ok when I compact. Can i relevel once the hardcore is compacted?

2. How much cement will I need for 15sqm if I can get 25kg bags from wickes? Does it need to be a specific type? Also is there anywhere else I can get it cheaper?

Thanks

 

[shenks]

Few things to think about...

1.

I have put approx 7cm hardore into the hole

Is this broken bricks and stuff or proper crusher run?

2. Are you using pre-cast concrete or natural stone slabs?

3. Will there be anything other than foot traffic on the patio?

Generally speaking a 50mm solid mortar bed using a 6:1 sand/cement ratio would be the norm. This would be about 8 and a bit bags of cement and about 50 bags of grit sand for 15sq m

Get your compacted sub-base as level as possible before starting on the mortar bed - it makes things easier in the long run.

 

[Rhbeen]

Would like to clarify........... Is a sand to cement mixture of 6:1 definately the correct proportion that i should mix to lay as base?

I found a 850 kg bag of SHARP SAND (assuming that sharp sand is the right type) from wickes:

http://www.wickes.co.uk/Aggregate-Sand+Ballast/Sharp-Sand/invt/220081

Using the 6:1 mix, that means 142kg of cement

FINALLY....Should i then compact the mortar layer before placing the patio slabs directly on top?

 

[shenks]

6:1 is the normal bedding mix... and you should wet lay the slabs rather than a dry mix. Don't use the '5-spot' method sometimes advocated by DIY programmes on TV as this is only good if you like leaving voids beneath the slabs and getting potential problems in the future..

The sub-base should be properly compacted prior to the mortar bed being laid. Crusher run (MOT/Dtp Type 1) is good as it has the right mix of fines and solids to form the sub-base.

850KG of sand (grit/concreting/sharp or whatever) is probably not enough as you would only get a 30-35mm bed which is a bit light. 50 bags at 25KG a piece is 1.25 ton.