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Posted: Thu Sep 03, 2009 4:27 pm
by Skyman
Hi,
Novice here having a go at a diy patio project would appreciate some advice. I shall be laying about 55sqm Indian Sandstone in total, comprises about 30sqm of patio and the rest as a path running from patio down one side of garden and across the back in front of an outhouse. The subsoil is clay, so I shall be using 150mm type1 base and laying flags on a full mortar bed. I have two questions, ther're probably dumb questions but I need a litte reassuring ...
Q1. The patio slopes away from house, but ends up a little below level of bed and lawn which I intend to retain with a run of railway sleepers on edge bedded in concrete. To deal with patio drainage, I'm thinking of installing linear drainage between edge of patio and sleepers. However, this does entail alot of extra work, am I being excessive? Is there a way to anchore the sleepers whilst still alowing patio water to run off below? Or am I doing the only sensible thing?
Q2. At a couple of points on the paths I have to step up a small amount. I intend on doing this with a single course of engineering bricks (matches other existing feature walling). One of the 'lifts' will also require the bricks to run all the way along under one visable edge of the path. So I'm assuning all these bricks need a small strip foundation, say 100mm deep by 200mm wide. Given the underlying clay, is it best that this foundation need also be on another 150mm of type1 bed as well? It's quite a bit of excessive work for such small changes in level!
This web site has been a completely brilliant resourse.
Any feedback much appreciated.
Posted: Thu Sep 03, 2009 6:55 pm
by Tony McC
To where would the linear channel drain? Have you considered that?
If it were my project, I'd use summits and valleys to drain to a point gulley rather than be messing about with all that linear drainage.
Brick risers for steps: they'll be fine bedded on 100mm of concrete direct on the sub-grade. No need for a sub-base unless you're building up levels.
Posted: Thu Sep 03, 2009 9:23 pm
by Skyman
Thankyou so much for your response.
The linear drainage would be piped down to nearby SW system. The SW system is quite deep though and it is the digging down and getting onto this that is the hard bit. I wasn't so much concerned with laying the actual linear channels and I think I prefer the idea/look of this than the valleys and gullies which would still need the same work to get onto the SW system (maybe more work, if more than one gully) . Does that sound fair?
Just wanted to check that I wasn't being excessively concerned about the patio drainage? Or if draining into the garden (under the sleeper retainers?) was an option from a 30sqm patio? Probably not, guess I'd better get digging.
Thanks again, brilliant site.
Posted: Thu Sep 03, 2009 9:26 pm
by lutonlagerlout
when you say it slopes away ,by how much?
linear gully draining to a soakaway will be a proper job, i find injun stone (especially the large units) difficult to turn and twist into a gully
LLL
Posted: Thu Sep 03, 2009 10:02 pm
by Skyman
Hi LLL,
The patio will have only a minimal fall, about 1:60. Most of the width of the patio will meet a flower bed (retained by the sleepers on edge). I had wondered about putting a rubble soak away under the flower bed, (which would be good for the flowers as well), but read some where on here that soak aways don't really work on clay ground?
Could also be more digging out than getting onto the SW actually.
How much soakaway would be need to cater for 30sqm of patio on these heavy clay conditions?
Cheers
Posted: Fri Sep 04, 2009 7:33 pm
by Tony McC
Depends on how 'heavy' is the heavy clay. If the garden doesn't flood at the mo' you'll probably be OK using summat like one of these babies
Posted: Fri Sep 04, 2009 8:08 pm
by Skyman
Thanks, I hadn't seen those drawings and that may well do the trick, will certainly consider it.
If I were to stick with the full linear drainage solution, another problem has occurred to me. I think I would need to lay the drains before the patio (piping to SW runs under patio), therefore I would need to know very precisely where the flags will end. The flags will be a random layout using 300x300, 600x300, 600x450, 300x900, 600x600 and 600x900, the patio is 4.3m back to the house, is there a way of calculating the overall allowance for pointing?
Also, even with a calculation for pointing allowance, would it me sensible to start laying from the drainage and work back, with cuts at the house side?
Thanks again, service is like magic. Cheers
Posted: Sat Sep 05, 2009 12:19 pm
by Bob_A
Skyman wrote:...............is there a way of calculating the overall allowance for pointing?
Also, even with a calculation for pointing allowance, would it me sensible to start laying from the drainage and work back, with cuts at the house side?.....................
Other than 'bump' your thread I can't help but I was going to ask a similar question.
I stand to be corrected but I think most slabs/flags are manufactured slightly smaller than stated so that after pointing you get the size quoted.
Whether this is the actual case in practise over large areas I don’t know.
So if anyone can help answer Skyman it'll help me 
Posted: Sat Sep 05, 2009 1:30 pm
by mickg
seeing as the drainage connection is under the new patio what is being flagged I would make the connection for the drain extending it to where the linear drainage channel is going and leave the pipe approx 150mm longer than required and cap the end off using an old plastic bag or similar, back fill the hole and cap off with a lean concrete mix to stabilise the ground around the new pipe.
to make sure the drainage channel and the new under ground pipe with the p trap connect in the correct position you can lay the linear channels out along the ground to see where the best position is for the outlet keeping the straightest run of pipe
lay the patio starting at the house with your mix of flags with the required spacing between each flag and work towards the drainage channel, the last row of flags to this channel can be laid out dry to use as a marker for the position of the channel, this will also be a check to see if this line of flags are still straight, if not adjust what you have laid accordingly as they need to be in a straight line so they fit snug up to the linear channel
now you can make your drainage connection as you know the exact position
the reason I do this is flags can vary in size and what ever maths calculation you do it will not make a 605mm x 305mm flag fit into a 600mm x 300mm hole with the same spacings as its neighbour
Posted: Sat Sep 05, 2009 2:11 pm
by lutonlagerlout
agree on that mick,you would think that with 300mm modular slabs you could put an edging in at 3060 mm allowing for 10 mm joints
but it never works like that
LLL
Posted: Sun Sep 06, 2009 11:30 am
by Tony McC
There are two options: dry lay the flags to get an indication of where they will end, and then allow an extra 10-15mm 'to be sure' OR have it all meticulously planned in advance by someone who can work out just which flag will go where and produce what overall width - if only there was such a person! :;):
Bob_A is almost right. Some manufacturers/suppliers publish size information that includes a joint width of a given amount. This is particularly unhelpful as you always have one edge of a path or patio or driveway that doesn't abut another flagstone, so the overall predicted width is immediately out by the pre-determined joint width, but with all random layouts, the joint width *has* to vary for the reasons explained here. So you may have a joint width that averages 10mm but it won't necessarily be 10mm for every joint.
That has been the cause of layouts being sent back to me because the client, who knows all there is to know about paving what with him being a vet, said ion his email dated 1/2/09 that he wanted the joints to be 10mm. Tit!
Most manufacturers/suppliers, however, publish 'nominal' size information which is the actual size of the units as near as dammit. This then causes problems for pedants who want to order exactly 10m² and don't factor in the joint width and then enter a state of apoplexy because they had determined that by using two 560x560 flags side by side, their path would be exactly 1120mm wide and therefore they would need exactly so many flags.
The one that really, really bugs me though, and there's never a week goes by without someone asking it: "I've got a 50m² driveway to block pave. How many blocks do I need?" 
