Help me to prepare? - I'm getting confused!

[nme]

ok, so i've take the plunge and decided to take on the next diy job of landscaping our garden. I've picked out some Truestone Ruby Indian Sandstone from these lovely peoplewho've been very helpful.

Explaining that I'm going to be doing this myself, I found they were very helpful, and helped me to work out a random pattern, and explained some of the core issues in laying the sandstone.

I was advised that I would need to dig out about six inches, and that i would then need to lay down 2inches of MOT hardcore, compact, then lay down a further two inches of sand, compact, then lay the stone on a full mortar bed.

OK, so i've started digging out to the required depth, but I didn't feel fully happy about the instructions, which is why i've ended up here!

Reading around this site, I'm really confused about the instructions i've been given by the supplier, and even more about the preparation that I haven't done yet. The big questing is about hardcore / subbase. I was told I'd need one for a patio, and the website does confirm this here, but I'm reading on this site that I dont really. Whats the case in regards to this sandstone? I guess that this is extra expense, and time, but assume, that now that I've had it delivered and dug out to the six inches, it won't hurt to lay the subbase anyway - true? Comments?

Secondly, I need to better understand how to work out the fall in the patio, and also to mark it out. Which is where i'm hoping you'll help

I am laying a patio about 4 X 9 meters. The 4 meter edge will butt up to the edge of the house, and this will be 150mm below the DPC.

I realise I'll need a fall away from the house, but also away to both sides. The same page on the suppliers website talks about a 1:40 fall here In the examples here it's sugested at 1:80. Is 1:40 correct for indian sandstone?

Also, once i've put down the subbase, whats the best way of making sure i have the right level in depth and the right fall? Should i use a striking off board as has been suggested - about 4 meters wide? That would mean i would need to put down some timber strips on the edges of the patio at the right slope to use as a guide. How else can i achieve this? How do you proffesionals do this?

I have a few other questions, but dont want to confuse this even more until i have understood the above.
Can anyone help?

Thanks
Nathan

[nme]

oh, and just one final thing, working out the fall using a 1:40 fall, i end up having the far end (9mts away from the house) at being 375mm below the DPC and tapering on the edges at 425mm below dpc - that sounds like a lot to be, and to be honest, I dont think i've dug out enough. Can someone help me to confirm these figures?

Thanks
Nathan

[nme]

help? Anybody?

[Tony McC]

You do NOT need a sub-base for a patio, although you can use one if you've a lot of build-up or if you like doing lots of extra work. I'm familiar with the info you've seen in the Stonemarket brochure, but it's less than ideal and is not the sort of build-up that would be used by the majority of contractors. As with most other companies, you have to bear in mind that Stonemarket are manufacturers and not contractors, so their advice tends to err on the side of caution rather than be based on years of experience.

Similarly when it comes to falls. 1 in 40 is the BS requirement for crossfall, but this is for crossfall on public footpaths and carriageways. 1 in 40 on a patio is a little excessive: yes, it does a great job of draining the paving, but you can't get the tomatoes to stay on your plate of salad when enjoying an al fresco meal at the patio table! 1 in 80 is an absolute minimum for any paving while 1:60 is comfy for most patio paving. However, for riven paving, to ensure better-than-average drainage and reduce retention of water on the surface, aim for 1:50. So, for your 4 metre span, aim for around 70-80mm of crossfall.

When checking levels, and when laying the flags, for a 4 metre span, a timber straightedge is too unwieldy and unreliable. We'd use a taut string line, fastened to line pins, as described on the main website.

[nme]

Thanks Tony,

That is great stuff! So can I confirm, on my patio i should aim for a crossfall of 1:50. I'm not certain I understand but is crossfall different to fall? I understand that crossfall is the gradient of the patio from the center to each of the edges along the 4mtr span. Is this different to fall across the 9mtr length?

A B C
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D E
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F G H

So in the above example, edge A,B,C is the 4mtr span, and A,D,F is the 9mtr span.

So is crossfall only the fall from B to A and B to C, whilst fall is fall from A to F or C to H.

Or is crossfall and fall the same?

To understand better, does the 1:50 crossfall mean that I have a fall from B to A of 40mm and B to C of 40mm, or do I have to have a fall of 80mm from B to A and B to C?

And what does that mean the fall should be from A to F?

Sorry if this sounds really thick, as I mentioned, I am very confused!

thanks
Nathan

[Tony McC]

Crossfall is fall across the main axis of the pavement. Imaging a long footpath beside a road: crossfall is the fall from the back of the path out to the kerb.

Endfall is the fall along a pavement's main axis, so, in the footpath example, endfall would run parallel to the kerbline. Both crossfall and endfall are falls, but they are falls in a specific direction relative to the paving.

On your project, you would have crossfall from A to C, from D to E, and from F to H. You could also have endfall from A to F (or vice-versa) but that just complicates thing at this stage.

I'm not sure why you think the mid-point, labelled B in your diagram, is relevant. It has no bearing on the construction work in hand. The crossfall has to cover the full width of the patio, as I stated in the last sentence of the second paragraph of my earlier reply. You need 70-80mm crossfall over the full 4 metre width of your patio.

[nme]

Tony,

Thanks for all your help, it is much appreciatted. I now understand crossfall, and what i need in my patio.

Just one further and final question. Do I also need an endfall, or is just a crossfall ok, and should the endfall be the same as the crossfall. My house runs along the 4 meter edge.

Many thanks, and apologies for all the questions.

Thanks
Nathan

[Tony McC]

Just crossfall is adequate.