Laying slabs without hardcore

ash1212002 · 18 Jun 2021

I'm planning to lay 600x600 patio slabs, the soil is quite solid as its clay

I was thinking of laying the slabs on a 50mm bed of dry mix of ballast and cement and then compact with a wacker plate

Or alternatively use a dry mix of sharp sand and cement

Would this be ok?, thoughts would be appreciated

mikeey84 · 19 Jun 2021

It's difficult to say, lots of people have patios built like that which don't move a mm, however the standard is at least 100mm of hard-core.

I wouldn't whackerplate slabs, as they would be likely to crack.

Bed should be 50mm of damp mix, sharp sand, say 6-1

ash1212002 · 19 Jun 2021

mikeey84 said:
It's difficult to say, lots of people have patios built like that which don't move a mm, however the standard is at least 100mm of hard-core.

I wouldn't whackerplate slabs, as they would be likely to crack.

Bed should be 50mm of damp mix, sharp sand, say 6-1

Apologies i should have been clearer, the whacker plate would be to compact and bed the 50mm damp mix and then lay the slabs on top, I will not whacker plate the slabs

Would sharp sand be the better option instead of ballast?

mikeey84 · 19 Jun 2021

If you are going to the trouble of hiring a wacker plate, you'd be as well to dig out a bit more and put 100mm of mot type 1 in.

You don't whacker the mortar, you need it quite loose so you can tap the slabs down to get them level.

As far as I know, sharp sand is the better option, but no idea why ballast wouldn't work. I'd buy sharp sand, but if you already have the ballast I'm sure it would work

Ian H · 29 Jun 2021

I’ve just put mine on 50mm of wet sand and sharp sand mix on a hard clay/soil base.

There’s a low bit that I brought up with MOT

JohnD · 29 Jun 2021

You can, but you have to consolidate the base very firmly.

I read a book by a construction engineer who, experimentally, laid a 2 inch deep concrete path round his house with no base except whacked soil, and said it astounded his colleagues by not cracking.

I wouldn't do it myself, though.

I had my own done following @noseall method and it is splendid

https://www.diynot.com/diy/threads/top-tips.482618/#post-3908222

ash1212002 · 29 Jun 2021

Would you recommend a 6:1 or 10:1 mix?

Also the 'dry' mix of sharp sand and cement is any water to be added whatsoever?

I've got plenty of hardcore/rubble so will be laying that down then wacker plate it followed by the weed membrane and then lay the bed of sharp sand/cement for the slabs

Ian H · 30 Jun 2021

I did mine 5:1 wet. I’d done a couple of other areas in the last couple of years exactly the same:

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Laying slabs without hardcore

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