The Brew Cabin

Hi Tony,

what a stunning site. I am contemplating (being nagged into!) laying a patio. It is fairly large (70m2 approx) and I have some beginners questions......

1) Drainage. The patio would be L shaped behind the house and around the garage (see diagram below). As the length ot the patio is around 12 metres, if I was to drain down the length of it, the bottom end would end up below ground level. Now I know that I shouldn't drain towards the house, but what about immediately alongside the garage? I was thinking about the linear grid drainage with slopes towards it from both sides.

HHHHHHGGGGG
HHHHHHGGGGG H=House
PPPPPPIGGGGG G=Garage
PPPPPPIGGGGG I= Drain
PPPPPPIGGGGG W=Wall
PPPPPPIGGGGG
PPPPPPIPPPPPP
PPPPPPIPPPPPP
PPPPPPIPPPPPP
PPPPPPIPPPPPP
WWWPPPWWW
Also, would the linear drain have to have a fall along it or is it filling enough for it to run out?

2) Edging. I am going to put soldiers around the patio, but, as the proposed patio is framed by the house, garage, wall, and concretegravel boards on each side, do they need to be concreted in?

I am sure that I will have tons more questions, and if I proceed, I will take step by step pics for you to use on the site if you wish.

PS, I am thinking of using Tegula Drive set - what are your opinions on this as a material?

Cheers and Regards

JayHoe

Using a linear drain is fine, but it has to outfall somewhere. Is there an existing gully or pick-up point somewhere along the edge of the garage?



It could go in with no fall, although it would be better with a slight fall, say 1:100, but it will have to be lower than the rest of the paving, which should slope towards it at around 1:60. So, it may be that the Linear drain is actually 200mm below dpc rather than the usual 150mm below dpc.

For the perimeter Soldier courses, I always prefer to lay them on a lean-mix bed of semi-dry concrete, say 10:1, as that ensures they aren't dislodged while laying the rest of the paving. Where they're up against an existing wall, there's no need to haunch, obviously, but they will need to be haunched at any free edges.

Looking forward to the piccies, and don't fret; you can't go wrong with the Drivesett - it's one of my top 3 pavings in the UK. :)

Thanks for the swift reply Tony.

Doh! You are quite right! Their are down pipes on the end of the garage that then head off under the proposed patio to an existing dispersal (yeah right) system on the lawn beyond the wall. (Dispersal cos a soak away doesn't like to work in solid clay).

This would mean that I could put a real gentle flow on the drain up and down to meet at the bottom left corner of the garage. Bonzer!

I am now thinking about the order of tasks.

1) Dig out whole area
2) Lay edging in concrete
3) Lay drainage channel (concreted in??)
4) Lay sub base & compact

Enough for now! Perhaps you can confirm I am ok so far.

Also, access to this whole area is either thru the house or thru the garage (side door over the proposed linear drain. Where is it best to start laying if I am not supposed to walk on screeded sand?

(Also just thought, not having done drainage before, how do you cut into and join to an existing pipe (I believe it is a clay pipe). Alternatively, I may just revert to draining from the bottom end of the linear drain, thru the gap in the wall and connect directly to the dispersal system (perforated plastic pipe surrounded with gravel)

Thanks

John

Your Sequence of Operations is right, but I don't envy you having to trek everything through the house/garage.

When it comes to laying, screed off the entire area, find your way back to the house/garage by walking on the soldiers, then start placing the actual paving from the doorway, and gradually work your way out.

There's a thousand and one ways of connecting linear drains to existing. With there being an existing pick-up point at the corner of the garage, then a simple outfall connection unit is probably the best way, but it depends on the type of Linear Drain you use. Some don't have outfall units, so you'd need to cut out a hole in the base of the channel, and bed this on mortar directly over the existing pipe, once you've removed the existing hopper or gully and fettled the pipework accordingly.

What's there at the moment? Can you describe or send in a piccie?

Glad the sequence is OK. I don't envy me either having to cart it all thru the garage.

I will take a couple of pics over the w/end and send them in. As for the existing drains, I have one d/pipe in the corner of the house/garage, and 2 at the end of the garage. All 3 join up some where(!) but I didn't see how the builder connected them up. They then head off straight down the garden.

I hope to start digging out tomorrow, so I may well have an exploratory dig. However, there are no rodding points or anything along the underground pipe work, so I am a little concerned that dust/and dirt walked onto the paving will block up the drainage quite quickly (perhaps I am just over concerned).

I will send the pics to give you more idea of the general layout.

Cheers

John

Any dust or dirt should be caught in the P-Trap, but anything that is carroed around the trap in suspension will be flushed along the system and should not cause any problems. However, if you have any parts of the drainage system open during the works, cover it with a board or a placky bag or summat to keep out the worst of any muck that's lying around.

Good luck with the digging - I'm off for a long weekend in the country. :~)

Hi Tony, well, I have started to dig out (my front garden is now one great pile of dirt, and we have only so far dug out a quarter!

As for the drains, I see that it would be no problem to connect in the linear drain, but we have another difficulty. As the drainage goes down the garden to a herringbone subsurface dispersal system, it is only about 3" below the surface. Can I block over it? The clay pipes themselves would only have sand bedding over them, no hardcore. Would a plate compactor smash them? Lowering the drainage is not an option.

Any ideas?

I have been trying to decide if it may be better to pave the area instead. If so, do I need hardcore? of is just a sand/grit bed enough. I have looked at your site and was wondering if the following is correct...

Hardcore where necessary (filling and sof spots)
Sand grit bed (what sort?)
Rake in cement immediately prior to laying an area
Wet mortar bedding (How thick, is it necessary?)
Slabs

Arrgh! Going mad here!

Hope you had a good weekend,

Regards

John

That drainage is terribly shallow - is it just collecting from the rainwater pick-ups? It really ought to be at least 300mm deep. You can't lay block paving over a land drain so shallow, but you might get away with laying flags/slabs.

Your order of operations is basically correct, but I'd try to make sure that the shallow drain is bridge by a larger flag and doesn't have a joint directly over it or one of the smaller flags. Lay the flags on the grit sand/cement bedding; no need for a full mortar bed if you're using a semi-dry grit sand/cement.

Have you thought about what type of flags you'd go for?

Tony,

the drainage is for rainwater from a flat roof extension and pitch roofed garage. Our soil is very poor draining and so a soakaway just wouldn't work.

Sounds like slabs are the way to go.I am still unsure on the bedding though. Do I just level off the grit, addcement powder, rake it in (all dry) and then plonk the slabs on top? Do I add water at any stage?? How much cement per square meter?

I have been looking at Marshalls slabs (and obviously the blocks before hand!). Any recommendations? I do not want to lay huge slabs as I had experience of this in my green house and moving them around nearly killed me. I quite fancy using rectangular slabs laid in stretcher bond.

Sorry for all these questions TOny, but I am a great believer in doing things right the first time!

Much appreciated.

Is there no mains drainage at all that could be used for surface water? If you're doing all this work, you might as well get the drainage solved once and for all.

Marshalls flags - depends on the look you're after. I really like the Perfecta flags for patios, but you might be after, say, a riven type or summat more decorative. Have you seen one you fancy?

With the bedding, there's usually sufficient moisture in the sand to initiate setting of the cement, so it's a simple matter of adding the cement and stirring it in. You can mix it all in one go and then spread it out as required, in which case you should mix 1 x 25kg bag of cement with 6 x 40kg bags of grit sand, or, if you're butying in bulk agg-bags, then it's 4 x 25kg bags of cement to each agg bag of grit sand.

If you're mixing in cement after spreading the sand, then, assuming the sand is around 50mm deep, each 25kg bag of cement should cover 3 to 4 m2.

You only need to dampen it down if the sand is very dry, and then, the best way is to spray it lightly with a hose. You don't want it sopping wet, just damp enough so that it clumps together when squeezed in your fist.

Hi Tony,

We are going for flags but haven't decided which ones yet. As for drainage, I was still going to add a linear drain and connect to my dispersal system.

I have been looking at your dry bedding mix page and you mention sand/gravel and ballast. Am I right in thinking that I can just use a sandy ballast, spread it and mix in cement, rake it out and lay?

Do the flags actually bond to the bed, or is it just that the bed 'firms up' so there can be no movement?

Digging out is proceeding, the first area was dug down deep enough for blocks before I hit the drainage(!) so I will have to back fill with hardcore. The next are is stripped of turf, the remainder will be tonight. We are asking a few people round on saturday to barrow dirt from the site to the skip. To break the (very hard) ground, I have been using my rotavator. This breaks up a 2-3" layer which is easily shovelled up, leaving a compacted layer beneath. Neat eh?

I noted on some of the Marshalls slabs in the catalogue it said they were to be mortar bedded. Is the 'firmed up' ballast/sand cement bed ok? or would they require a wet mortar? (I must admit I much prefer the idea of not using wet).

For the bedding, you can use grit sand and cement, or all-in ballast with cement, or grit sand, gravel and cement; whatever is readily available in your area. The idea of adding the cement is to firm up the bedding to prevent any settlement or erosion by groundwater, ants, etc., so there's no need for the flags to bond to the bedding. In fact, it's better if the flags don't bond to the bedding, as that makes any remedial work or replacement that much more difficult.

If the rotavator is breaking up the ground, then it doesn't qualify as 'very hard' in my book. Very Hard ground needs a mattock or a crowbar, and that's assuming there's no JCB available! ;)

Marshalls' DIY advice is basically wrong. Mortar bedding is more time-consuming, it's messier, it uses more cement than is actually required, it makes adjacent flags 'float' and shift from finished level when laying, it's a nightmare if any units need remedial work.....but, it makes the job seem easy in the catalogues and brochures.

Cement mortar bedding is not an accepted practice for site works, so I fail to see why it's ok for patios. Use a coarse sand bed or a semi-dry 10:1 grit sand cement bed - leave Mortar bedding for the Blue Peter School of Flagging!

Tony,

great, I will use an all in ballast then as I would assume that it would be inherently more stable than grit.

I understand what you are saying about the slabs not bonding to the bedding. (and I am glad I won't have to mix up all the mortar!!! :-) )

OK, so the ground isn't JCB hard, but it is VERY compacted. Last night I used the rotavator on the last section of grass (I would hesitate to call it a lawn) and it dug in about 1/2", just enough to remove the grass. When I go over it again, it will bite deeper, but it is a large rotovator and it is very hard work to get it to dig. By comparison, I recently dug over my veg plot with it that has lain undisturbed for a year and it bites down 6" with ease. So comparatively this area is hard.

I did take some photos of the area before I started, so I will take some of how it is after we have finished on Saturday and will send them in.

Thanks again for your help and advice, it is much appreciated, and I will certainly drink a toast to you on completion.