To lay MOT sub base or not?

[pilsbury]

I'll be extending my kitchen out sideways and I'm in the process of planning the works and what I need to do.

The current kitchen floor level is 315mm above ground level. This will be the extension FFL as well. The ground I'll be laying my new floor slab over is covered with dark blue clay paviers that are solid and have been there since the house was built (1925). There is a slight undulation due to settlement over the years, but that I'm sure would have stopped many moons ago.

Do I need to remove these and whacker a sub base down, or can I just lay a level sand blinding down on top of the paviers then DPM and 150mm concrete slab, 100mm insulation and 40mm screed on top?

 

[23vc]

I'd say it's the building inspectors call. In my case they are happy with treating the existing garage concrete floor as the hardcore layer and going over that with the dpm.
You need to think are you happy with the stability of it or if it's worth the extra cost and time of breaking it up etc

 

[23vc]

Also wouldn't you want a bit thicker on the screed and less on the slab or are you using a pumped screed that can go thinner?

 

[pilsbury]

Will chat to BC about it. I was thinking of a pumped screed but I'm aware I can go less thick on the slab and up the screed depth.

 

[23vc]

I've got exactly the same issue where 40mm is my Max screed depth so I'm planning on leaving the screed out and try to finish the slab as best I can. I've Screeded before but at a 65mm+ depth.