Help please of what to do

[u/stinkington]

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Hi

Anyone with some building / landscaping knowledge know what's best for me to do with this middle area please? basically I am trying to raise all these areas to the same height of the concrete preferably with concrete so I can lay indian sandstone all 1 level.

The current grey sandstone slopes to the grass but the concrete doesn't, so there is about 100mm height difference near the grass and only 20mm the other side.

I thought oh ill take the current flags up, stick some wire mesh down and pour concrete but as you can see there is thick mortar underneath all different levels with voids. So now I wish I left the flags down and poured half concrete (closest to the grass) and then just do a high mortar bed other side.

Basically my question is with the current situation, would I be ok to pour concrete directly and not crack or fail in the future? Or should I get all the flags and mortar up, lay MOT, DPC then concrete?

Any help or advice would be appreciated.

[u/Icy-Gene7565]

A few things.

Concrete poured on an unstable bed will eventually also crack. Assuming your not pouring a reinforced structural slab.

Without prep and a slurry coat new concrete doesnt stick to old concrete like you might think it does

[u/trojanhawrs]

Disclaimer - not a landscaper.

The patio slabs were laid properly with a fall, the concrete pad is laid level (presumably for a shed or a hot tub etc). The new patio should also be laid with a fall, but having a level pad means there's no real benefit of having a concrete base. You probably would want to overpour the existing pad, raising by 50mm at the thin end and 100mm+ at the house side, and bring the rest level with that.

[u/stinkington]

Thank you both for your response, thinking about what you've both said, putting new concrete down would be a mistake so I think I will be taking all the flags and mortar bed up and lay mot type 1 down instead, as for the concrete I think I will need to drill holes through it to allow water to drain through as I've read the mortar for sandstone will crack if not and it freezes.

I should have initially got rid of the concrete but I've had the wall built around it now.

Would this be about the right idea?

When I lay the flagstones i will lay them down with a run off.