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Posted: Mon Apr 14, 2008 1:18 am
by alantren
Firstly, can I say how easy to use and understand, informative, friendly and enjoyable this site is. I couldn't believe how much expert knowledge I was getting for free! Being a northerner myself, I appreciate that you talk about flags rather than slabs and the humour in your comments really appeals.

Anyway, for reasons best known to my wife, I am re-doing and extending our patio. It's an early 1930s property and there is a simple patio laid up to the limit (below dpc), next to it a small concreted area and then the driveway, which is in a sorry state.

Question 1 - quick check - the dpc is just above this concrete render, isn't it?
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The existing patio, on the right of the picture below (which is actually of the proposed layout), that I think was laid by a decent contractor, is 5m x 4m, plain square flags that appear laid on a soft sand/cement base under which is concrete. There is a 5cm depth between the concrete and the top of the existing flags I intend to break out the last metre or so for a bit more greenery and extend this patio to the kitchen door, raising the existing concrete area (which is 15cm lower) for about 1.5m x 3m. I've got a fair bit of concrete breaking already in this project, so I really don't want to leave dig this area up too and so intend to lay on the concrete bed. The flags I will be using (Stonemaster Yorkstone) are thicker and will also require thicker mortar bed which would bring the level up to 10 cm below the dpc so it looks like I need a long linear drain.

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Question 2 - As the paving will run level along the house wall, how can I lay a 5.5m channel drain with a suitable fall but still have the grating level with the pavement along this length? There will be no foot traffic here so I think I can use a Class A channel drain with a metal grate but I can't find a supplier of this on t'interwebby - can you point me in the right direction?

The second area (to the left) I will pave is at a lower level that I want to maintain, if I hack out the concrete there and dig down in a currently grassed area I think I can get a suitable fall that starts at the same height as the existing concrete. However this is at the corner of the house and on the driveway there is a garage and I will putting in a shed too. I am also intending to dig up the driveway at this area.

Question 3 - How are the falls managed in situations like this?

Questions 4 - Using crushed concrete as a sub-base, does it need to be retained in some way while it is thwacked (using a hired whacking plate)

Question 5 - and, working to the nearest cm, how thickly do I lay it initially for it to be compressed to 80mm from eight passes?

I will post some pictures as the work progresses, maybe others can learn from my mistakes, or be inspired to do better.

Last question - At the end of a day of digging or lugging, which ale would be most suitable for re-invigorating me if the weather has averaged between 13 and 17 degrees.

Thanks for reading this far
Alan

Posted: Mon Apr 14, 2008 8:05 pm
by Tony McC
Q1 - yes, it should be

Q2 - you don't strictly need a fall over such a comparatively short run. Any surface water findings its way into the channel will 'push' itself along under hydrostatic pressure: as more water enters the channel, it 'pushes' existing water towards the outlet.

Try Clark-Drain for your channel supply, but be aware that metal gratings are more expensive than placky and not as discreet in residential applications. Aco offer a black japanned style grating for their Hex Drain range.


Q3 - Greatest fall is diagonal to paving layout, that is, it's aimed towards the lower edge of your sketch.

Q4 - no, but it needs 'spread'. I'd suggest a spread equal to or greater than the depth of sub-base.


Q4 - Too many variables to give a definitive answer. Trial and error is the only way to determine just what degree of compaction is possible on your site using your materials with your compaction kit. Start with approx 110-120mm.


Q6 - Theakston's XB or Guinness.