Posted: Thu May 28, 2020 10:51 pm
Hi all, firstly thank you for all the posts and information on this site. Has been so useful in planning my project. So the bulk bags arrived today and the compacting plate arrives tm and I've suddenly begun to doubt myself!
We have excavated an area 6.67M long x 3.57M wide for a new patio to a depth of 170mm in addition to the existing patio we have by the house, which is 3.31M long by 5.54M x wide, where we have removed existing slabs and the rubbish mix of sharp sand with the odd spot of cement that they were laid on. So we will end up with an L shape patio.
Underneath the existing patio is a 100mm deep MOT Type 1 base, which we are reusing, but we will need to rough up the surface and compact / level off again as there wasn't really a drainage slope before and there were dips in the base height, not where it has sunk, but where more sharp sand was used to level it out instead. The 50mm concrete slabs hadn't shifted in 16 years so am reasonably happy with it.
On the new "second patio" I was going to whacker the soil, lay membrane, lay 100mm compacted MOT Type 1, then a 35mm full mortar bed and 35mm slabs (450mm x 450mm - Marshalls Perfecta). I was pretty confident this would be good enough for taking the weight of a hot tub we hope to add in future as it would be a static rather than dynamic load. Full, it would weigh about 2 - 2.5T. I've seen a 150mm sub base can support up to a 7.5T vehicle, so had thought I'd be fine with 100mm, but we do have some clay in the soil and are built on an old quarry site, so I'm having a last minute panic! Do I need a deeper sub base or is 100mm OK do you think?
Other than that, aside from where the Hot Tub will live, I'm planning on adding a 1 in 60 drop away from the house, although because our lawn is higher than the existing patio the first patio will end lower, than the second begins (I can't start higher at the house end as would not have the 150mm minimum before the DPC). So rather than joining the two, I'm going to run a 225mm gravel channel between the two, connected by one slab (either ramped up slightly, or built in as the smallest of steps). I've also got a 100mm gravel channel between the house and first patio and a 350mm channel between both patios and the wall/fence to the side, the thinking being that this will aide drainage to be safe (and if I totally cock it up I could always get a drain added, but I don't believe drainage will be an issue as isn't currently and the first patio is very sheltered).
If I do need a deeper base, my likely option would be to go for a 30mm higher second patio (so it would be the patio slab thickness higher than the adjoining grass), as digging the ground at this point will be very hard given the dry spell we have had - would anyone see a problem with that, other than mowing the edge of the lawn?! That would give me about a 130mm sub base, maybe 140mm, once I've whacked the soil.
Thanks a lot in advance for any advice.
We have excavated an area 6.67M long x 3.57M wide for a new patio to a depth of 170mm in addition to the existing patio we have by the house, which is 3.31M long by 5.54M x wide, where we have removed existing slabs and the rubbish mix of sharp sand with the odd spot of cement that they were laid on. So we will end up with an L shape patio.
Underneath the existing patio is a 100mm deep MOT Type 1 base, which we are reusing, but we will need to rough up the surface and compact / level off again as there wasn't really a drainage slope before and there were dips in the base height, not where it has sunk, but where more sharp sand was used to level it out instead. The 50mm concrete slabs hadn't shifted in 16 years so am reasonably happy with it.
On the new "second patio" I was going to whacker the soil, lay membrane, lay 100mm compacted MOT Type 1, then a 35mm full mortar bed and 35mm slabs (450mm x 450mm - Marshalls Perfecta). I was pretty confident this would be good enough for taking the weight of a hot tub we hope to add in future as it would be a static rather than dynamic load. Full, it would weigh about 2 - 2.5T. I've seen a 150mm sub base can support up to a 7.5T vehicle, so had thought I'd be fine with 100mm, but we do have some clay in the soil and are built on an old quarry site, so I'm having a last minute panic! Do I need a deeper sub base or is 100mm OK do you think?
Other than that, aside from where the Hot Tub will live, I'm planning on adding a 1 in 60 drop away from the house, although because our lawn is higher than the existing patio the first patio will end lower, than the second begins (I can't start higher at the house end as would not have the 150mm minimum before the DPC). So rather than joining the two, I'm going to run a 225mm gravel channel between the two, connected by one slab (either ramped up slightly, or built in as the smallest of steps). I've also got a 100mm gravel channel between the house and first patio and a 350mm channel between both patios and the wall/fence to the side, the thinking being that this will aide drainage to be safe (and if I totally cock it up I could always get a drain added, but I don't believe drainage will be an issue as isn't currently and the first patio is very sheltered).
If I do need a deeper base, my likely option would be to go for a 30mm higher second patio (so it would be the patio slab thickness higher than the adjoining grass), as digging the ground at this point will be very hard given the dry spell we have had - would anyone see a problem with that, other than mowing the edge of the lawn?! That would give me about a 130mm sub base, maybe 140mm, once I've whacked the soil.
Thanks a lot in advance for any advice.
. I'd describe the place we are at as light in colour and very sticky when wet - boots ended up five times their weight when I was walking around on it in the wet a month back (prob the clay content I guess). 