Gardening & Landscaping

Patio sub base meets concrete uneven edge

Anonymous user 11 March 2024 - 2.30 PM

Hi All I'm attempting a DIY patio installation of Indian sandstone flags, 600x900x22mm. I have several tonnes of Type 1 MOT ready for compacting. When digging out the soil I found that there are several layers of concrete and old stones already on there. The DPC even after installation will still be beyond 150mm so that should not be an issue. I also plan to lay a weedproof membrance under the motar type 1 MOT. Question: 1. Can I just compact the type 1 MoT up to the uneven edge of the current concrete and previous flags until it is level and then lay the 50mm motar bed on top when ready for placing slabs? (Image with red arrows) or 2. Would it be a good idea to place a temporary wooden straight edge in ground and dig out soil and pour concrete until it is level with the uneven edge. Creating a new even edge. Then type 1 MOT will be packed on the soil side nicely up to it. Image with red crosses show where concrete would be poured. I have also dug and found the rain water waste pipe and wonder if this requires any consideration. Plan was to simply compact type 1 mot on top. but this could cause some damage, should it be covered first? its hard to see but its under the wooden chairs. Any advice appreciated in advance. Thank you Colonel

Red Squirrel Gardening Ltd

Rating: 5 out of 55512 reviews

Bath

Providing the concrete base is solid and stable (no wobbly bits) i would do exactly as you said in question 1. Just compact the type 1 up to the edge of the concrete and then lay the cement/slabs on top as if it was all type 1. It doesn’t matter that the concrete edge is uneven. You are just trying to get a solid base for the mortar/slabs. You can fill all the gaps with type 1 and compact to create a full bed of type 1/concrete. If for instance there are parts of the concrete that arnt stable/wobbly then i would cut that section back to where it is stable and replace with type 1 and compact.

Answered11 October 2023

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A. Rose, Gardner

Rating: 5 out of 5553 reviews

Lymington

Agree with Red Squirrel thats absolutely fine. In terms of the waste, it should be surrounded by pea shingle first, then matting, then MOT and compaction. Finally, 50mm is quite a thick bed; I would try and bring the sublayer up if you can. At the same time, sandstone isn't as porous as it used to be so I'm now also priming the slabs before laying - it may not strictly be necessary but it prevents any future headaches. All the best Dan

Answered13 October 2023

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Chris Williams (Creative Property Services) LTD

Rating: 4.7 out of 54.7532 reviews

Ferndown

Your rain water pipe needs to surrounded by pea shingle and wrapped with membrane before you compact the type 1

Answered19 October 2023

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Kernow landscaping

Rating: 4.9 out of 54.9595 reviews

Redruth

Agree with Red squirrel, Yes you can dig down lay landscaping fabric compact 150mm of type 1 mot stone to same level of concrete remember to only compact 50mm at a time for proper compaction then lay with wet mortar 4:1 sharp sand cement and point slabs with a semi dry mix of soft and cement packed in well to joints to keep slabs clean use sponge water. Also if it all needs raising use concrete remember to not lay your paving level but a slight fall towards aco drainage channels.

Answered7 November 2023

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