Great site. Lots of help when I had my first stab at BP year before last (50m2 patio) still looking good.
I have an ugly concrete slab approx 24m2 that I want to BP over and preferably raise 150-200mm (it's currently 500mm below dpc). Can I build it up with sub base and bedding sand?
Alternativly, I could mortar bed blocks straight onto the slab and retain the current two steps but this looses me space.
If I bed on wet mortar, do I have to use mortared joints as I'd prefer not to.
Thanks
Raised Block over slab
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84-1093879891
There's a page on the main website that covers this - see Laying over a base and then come back if you've more questions.
Given that you want to elevate the levels, I reckon you could fairly safely lay 100mm of sub-base over the existing base,, and then the laying courses and blocks as per normal. Obviously you need to give some thought to how the sub-base would be drained, and how you'd construct the edge courses, but these are minor issues and easy to resolve.
Given that you want to elevate the levels, I reckon you could fairly safely lay 100mm of sub-base over the existing base,, and then the laying courses and blocks as per normal. Obviously you need to give some thought to how the sub-base would be drained, and how you'd construct the edge courses, but these are minor issues and easy to resolve.
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boltaction
- Posts: 2
- Joined: Fri May 28, 2004 9:39 pm
Tony
Thanks for your reply. I allready checked the relevent pages on your website but haven't actually decided which way to go, raised with sub-base over the concrete or mortar bedded directly onto the concrete.
What I don't really want is mortar joints in the block as advised in your "rigid construction" page. Someone suggested bedding blocks on dry mortar mix instead of wet to avoid wet mortar pushing up between blocks and creating a gap that would need filling with mortar. Is this a reccomended technique?
With regard to drainage, the existing slab is approx 2.4m wide and falls away from the house to lawn by about 40mm. I was also considering making the paving a little wider than the slab so water could drain here.
Due to height difference to lawn (250-300mm), edging will need to be low retaining wall rather than kerb units.
Thanks for your reply. I allready checked the relevent pages on your website but haven't actually decided which way to go, raised with sub-base over the concrete or mortar bedded directly onto the concrete.
What I don't really want is mortar joints in the block as advised in your "rigid construction" page. Someone suggested bedding blocks on dry mortar mix instead of wet to avoid wet mortar pushing up between blocks and creating a gap that would need filling with mortar. Is this a reccomended technique?
With regard to drainage, the existing slab is approx 2.4m wide and falls away from the house to lawn by about 40mm. I was also considering making the paving a little wider than the slab so water could drain here.
Due to height difference to lawn (250-300mm), edging will need to be low retaining wall rather than kerb units.
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84-1093879891
You could lay blocks on a semi-dry mortar, but you have to think about what depth of bed would be involved.
A mortar bed really shouldn't be more than 25-30mm in depth, so if you want to bring up the levels more than that, you'd need a concrete screed overlay on the existing base. Using a semi-dry material is always easier than using wet, and a lot less messy.
The crossfall you have is just about acceptable - 1:60 is the lower limit of what I like to see, but, if you're going to have a low retainer at the garden edge, how/where will the water drain?
A mortar bed really shouldn't be more than 25-30mm in depth, so if you want to bring up the levels more than that, you'd need a concrete screed overlay on the existing base. Using a semi-dry material is always easier than using wet, and a lot less messy.
The crossfall you have is just about acceptable - 1:60 is the lower limit of what I like to see, but, if you're going to have a low retainer at the garden edge, how/where will the water drain?