Tony,
I'm about to start a patio using saxon slabs which will extend 12 meters from the house. From my calculations, in order to achieve a 1:60 fall, the patio will need to be 200mm higher at the end adjacent to the house. Some of this area is already covered with a concrete slab. I plan to progressively build up the level using crushed hardcore, some of which will be laid direct onto this concrete area. Will this be ok?
Regards
Gary
Buiding up level for correct fall
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84-1093879891
The "crushed hardcore" over a rigid base should be ok where you can be sure there is at least twice the depth of the biggest particle. If, f'rinstance, you're using 40mm crusher run, then the min depth is normally 40 X 2 = 80mm. The thinking behind this rule of thumb is explained in the Sub-base FAQ.
In practice, you could get down to 40mm depth and get away with it, but you'll find you'll need to use material with a higher proportion of fines to minimise the number of voids.
For anything less than 25mm, I'd prefer to use a 10:1 semi-dry mix of grit sand and cement and wacker that in as a sub-base.
You can get away with about 1:70 fall with Saxons (or similar textured flags). John Higgins from Aintree Paving and meself were talking about these this afternoon - they're a nice flag but they don't half get dirty in next to no time, and the less fall the pavement has, the less likely they are to self-cleanse, so it's a matter of finding a compromise between creating sufficient fall to ensure the flags drain and do a bit of self-cleansing while not having a gradient that feels as though you're falling off the edge. I reckon 1:60-1:70 is about it for Saxons (and similiar).
In practice, you could get down to 40mm depth and get away with it, but you'll find you'll need to use material with a higher proportion of fines to minimise the number of voids.
For anything less than 25mm, I'd prefer to use a 10:1 semi-dry mix of grit sand and cement and wacker that in as a sub-base.
You can get away with about 1:70 fall with Saxons (or similar textured flags). John Higgins from Aintree Paving and meself were talking about these this afternoon - they're a nice flag but they don't half get dirty in next to no time, and the less fall the pavement has, the less likely they are to self-cleanse, so it's a matter of finding a compromise between creating sufficient fall to ensure the flags drain and do a bit of self-cleansing while not having a gradient that feels as though you're falling off the edge. I reckon 1:60-1:70 is about it for Saxons (and similiar).