Hi All, i have mostly created a new patio following the advice on this site from footers to walls and in fill with sub base. My problem now is that i have an area to be paved which is 8m x 4m. I understand the fall should be around 1 in 60 as i'm using riven sandstone paving but I'm struggling with 2 aspects of this. Firstly should the fall be cross or straight or both? This amounts to a significant amount across the whole planned patio (the 8m side) so i think it will look really obvious that there is a fall.
Secondly how can i get the sub base level and with the correct fall? I'm sure there must be a professional technique for doing this but i'm just dragging a plank of wood over the surface and it doesn't seem to work very well. Any advice much appreciated
NOt sure if i'm able to link to a picture but this may explain better, around 8m right to left, which is the natural downhill slope, just over 4m back to front Patio
Help with fall on new patio - Advice needed
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r896neo
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Personally with riven sandstone i try to lay to a 1:60 - 1:70 fall in 2 directions. This means that even heavily riven slabs will not pool.
In practise falling it in a single direction is probably more than adequate for domestic work. Riven stone (and some of the cheaper sandstone is very riven) needs a bigger gradient and if only falling in one direction i go for 1:60 as you suggested. Which direction you fall it in will depend on your drainage but in general terms try to fall it over the shorter distance as its will be less of a drop.
In my experience you will not start to notice a slope until steeper than 1:50. (unless you have a brick course or other level line to compare it to)
As for setting it out simply use pegs, a level and long straight edge. Put a peg in one corner to your finished paving surface height and transfer this level across to the far end of the patio and place another peg. Now you have 2 levels points to use as datums and take all measurements from now on off of these.
In practise falling it in a single direction is probably more than adequate for domestic work. Riven stone (and some of the cheaper sandstone is very riven) needs a bigger gradient and if only falling in one direction i go for 1:60 as you suggested. Which direction you fall it in will depend on your drainage but in general terms try to fall it over the shorter distance as its will be less of a drop.
In my experience you will not start to notice a slope until steeper than 1:50. (unless you have a brick course or other level line to compare it to)
As for setting it out simply use pegs, a level and long straight edge. Put a peg in one corner to your finished paving surface height and transfer this level across to the far end of the patio and place another peg. Now you have 2 levels points to use as datums and take all measurements from now on off of these.
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Tony McC
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Assuming that the logical fall is towards the camera in your photie, I'd suggest a minimum of 1:60, which over an 8m run means 135mm of fall. It sounds a lot but once it's down you'll hardly notice.
Sub-base is levelled in much the same way as the flags are laid. You need to establish level points at either end and then use a taut string line to check the actual level.
So, it would make sense to establish a taut string line along the back edge (as you look from the camera position) which represents the intended paving level, so that would need you to knock in a peg or pin roughly 300mm outside each of the two top corners. Fasten a string line to one pin at the level you intend the paving to be, and then stretch it as tight as possible to the second pin and fasten using a half-hitch.
Now, extend the string line down one side and set-up a pin 300mm outside one of the bottom corners. Stretch the string, half-hitch it and check the level using a straightedge and spirit level so that it matches that of the first line. Once you know this, you can move the level down by the necessary 135mm.
Next, run the string line across the bottom of the proposed patio, establish a fourth pin and set the string line as level from pin 3. This has given you levels on 3 sides and you could, if you wished, return the string now to pin 1 to give you a complete perimeter.
Now, when you want to check the level of the sub-base, you set-up a temporary pin outside the top line, one outside the bottom line, and stretch a string line between the two set to a level that just touches the lines you set up originally. This represents the intended level of the paving when complete. To check the sub-base, move along the line and measure down from the string line to the compacted sub-base. If you are using, say, 25mm flags on a 40mm bed, you need the sub-base to be 65mm beneath the line. This technique is known as "dipping" and I prepared a short 'tool box talk' and video on the procedure for a large tool/machinery manufacturer earlier this year who then decided to scrap the project and not pay me for my time and efforts. Bar Stewards!
Sub-base is levelled in much the same way as the flags are laid. You need to establish level points at either end and then use a taut string line to check the actual level.
So, it would make sense to establish a taut string line along the back edge (as you look from the camera position) which represents the intended paving level, so that would need you to knock in a peg or pin roughly 300mm outside each of the two top corners. Fasten a string line to one pin at the level you intend the paving to be, and then stretch it as tight as possible to the second pin and fasten using a half-hitch.
Now, extend the string line down one side and set-up a pin 300mm outside one of the bottom corners. Stretch the string, half-hitch it and check the level using a straightedge and spirit level so that it matches that of the first line. Once you know this, you can move the level down by the necessary 135mm.
Next, run the string line across the bottom of the proposed patio, establish a fourth pin and set the string line as level from pin 3. This has given you levels on 3 sides and you could, if you wished, return the string now to pin 1 to give you a complete perimeter.
Now, when you want to check the level of the sub-base, you set-up a temporary pin outside the top line, one outside the bottom line, and stretch a string line between the two set to a level that just touches the lines you set up originally. This represents the intended level of the paving when complete. To check the sub-base, move along the line and measure down from the string line to the compacted sub-base. If you are using, say, 25mm flags on a 40mm bed, you need the sub-base to be 65mm beneath the line. This technique is known as "dipping" and I prepared a short 'tool box talk' and video on the procedure for a large tool/machinery manufacturer earlier this year who then decided to scrap the project and not pay me for my time and efforts. Bar Stewards!
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