I've lifted a couple and they lifted easily which makes me think they are just on sand but what sand? There is some gritty sharp sand there but I think it must be mixed with something else. It's quite dark and moist. It can't be cement because surely the paving would have been stuck to it if it were? I think there must be some builders sand and something else?
It's hard to tell without lifting more but one slab had six inches or so of sand underneath but the next one only had two inches and then I hit a lump of concrete.
I don't want to lift too many more because I'll have to put them back until I am ready to do it properly!
I would have liked to have known what I was up against, so that I could plan in advance whether I would need a skip, hardcore, a breaker, a compactor, etc. but it may be that I have to take things one day at a time. Lift the patio, then see if I need to dig it all out, then order a skip, then hire the machinery. Still I suppose there is no rush when you are doing it for yourself, just the eyesore of bare ground whilst it is unfinished.
BTW I don't think there is any drop on it at the moment and puddles form in heavy rain so it will need a drop creating.
if it's been down for a decade, anything that was going to rot and sink, roots, stumps, weeds etc, will have well rotted away by now.
There isn't anything else that can cause ground to move, except geological phenomena and you have no control over this, so even putting the patio on
2ft thick concrete still wouldn't stop it from moving if this was the cause. I fear your patio has moved because it is laid on sand (reading your other post on this subject) and what /can/ occur in this instance is that the sand bed gets wet, then winter frosts cause it to expand, pushing the flags up, then it defrosts and sinks back down, but not always back into the position it started off at - sometimes the bedding sand is forced out of the joints, and insects also undermine the sand in summer causing voids etc, which is why I either use a solid bed of dry sand/cement, or lay the slabs directly onto compacted ground or hardcore on blobs of sand/cement
150mm is the recommended gap, about two courses of bricks. If the house has cavity walls you don't need to worry too much about this
there's a lot of bumph spoken about falls, usually with the misguided notion that water won't hold on any kind of slope, and my answer is yes it will -
1:40 is the absolute minimum and you should be aiming at more than this if it's possible. I can't understand why people try to get patios etc like snooker tables and then wonder why they are permanently wet - what's the big deal about having somewhere that slopes? - your patio is 4m? and if you use the 1:40 rule, it will run down 100mm in 4m, or to put it into context, 4 inches over 13ft 6.
This is borderline IMV and to employ the 1:100 technique would mean it would only fall an inch and half over 13ft 6, this is nowhere near enough - the slightest discrepancy in your laying and you've got puddles everywhere.
If you are laying on a solid bed, you mix it in situ, that is to say, you tip a few barrows of sand, then rake it out roughly where you want it to be, then throw half a bag of cement over it and rake it over thouroughly to mix it all together, it takes a few minutes and there's no shovelling involved
When I came to break up a concrete patio, ready for laying something more attractive, it was soon apparent that the gully had been cast into it, with the top of the trap only a few millimetres below the concrete surface. Once the damaged gully was removed, I discovered the next pipe,also taking the soil pipe output, had clearly been cracked for quite a while. The stirrup pump came in handy to empty the excavation, whilst I experimented in 3D geometry with a selection of plastic components. I was very fortunate that I was at the start of a run.
No shoveling involved, I like the sound of that! Do you need to compact it down or just tamp it with wood? You've denied me the chance to play with a mixer, are you going to deny me the hire of a whacker plate too ;)
Thanks for all your help. I've read your old posts on paving and know this is your livelihood so you know what you are talking about (as do the other contributors I am sure). Thanks everyone for your help. Now just to get round to it!
My old patio was all over the shop, up, down, wobbly slabs etc. Once lifted I realised it had been laid on what appeared to be pure sharp sand. I have since learnt that sand is one of the ingredients of soil - it doesn't (apparently) take long for nature to integrate your sand. Some areas had visible sand, others looked like they were direct on soil. I now realise that the sand had become soil.
I lifted the old patio, did all the ground work (retaining walls, proper
100mm compacted crusher base etc) but because of a complicated pattern, I opted to pay a firm to lay the new slabs. They did the 'pour sand, chuck on cement and rake' method. Within a year some slabs had sunk, some gone wobbly etc. I'm pretty disappointed with their work to be honest.
That is the limit of my experience of raking in cement on the ground. BUT - having watched these guys, I felt confident enough to lay the garden path and slab the new gazebo myself. Sand/Cement mixed 9:1 in the mixer as a bedding layer, some years later they haven't moved at all. I'm preparing to re-lay the patio *again* whereas the rest (which I did
9:1 in a mixer) doesn't need touching.
As I say, my experience is limited to that above, but, I firmly believe that properly mixing the bedding layer at 9:1 is the deciding factor so far (for me, IME etc).
Incidentally, I hired a crusher for a weekend and turned the old patio slabs (and all the other rubble in the garden) into crusher for a grand price of £120+vat. Much cheaper than paying for skips to cart away the old slabs and then buy in crusher.
If you're going to give it a whirl and lay them on a solid bed, you can't tamp it down or compact it at all until the flags are in place, and even then the underlying surface needs to be fairly level, that is to say, you can get the top of the uncompacted screed perfectly flat by trammeling, but if it's 2 inches thick at one end and four inches thick at the other, they will not compact down to the same finished level IYSWIM.
If you get your ground fairly level {1} and then use trammels (bits of 3X2) along each side, then fill in the area to be trammeled with your dry sand/cement and pull another 3X2 along the tops of the other two to create an even flat bed of raked sand/cement. Then p - l - a - c - e each flag in position carefully and squarely, don't let one corner tip into the bed, then tap the centre of each flag as you lay them so that the mixture underneath is compacted evenly.{2} The term 'solid bed' is actually a misnomer here because the finished product is actually biscuit like in texture and allows water to penetrate somewhat, provided you use grit sand and not builders sand. The main drawback with this method is that you need wings, or the ability to float because you can't stand on the trammeled area otherwise you will compact it with your feet, the answer to this is to trammel only a 3 foot section, the full length (or width) of the area to be paved, pave that and them work yourself away from it, ignoring any cuts around the edges - these can be laid later once the main body has set. I use this method for vehicular traffic but it's not really required for foot traffic, but the choice is yours.
{1} If you want to play with a whacker for a while, hire one for a day, but only once the area is cleared of all flags, bits of concrete etc and you have levelled it up with whatever you are using, mot might be a bit too rough if you aren't raising the area much, grit sand is perfect and packs down very solid. Soil doesn't pack down at all and the whacker just sinks, stone doesn't pack down too good neither
{2} Also when tapping down, use a flagging mall, available from any hire shop for a fiver a week, or if you are feeling flush, you can buy one for 20 quid, tap each flag the same amount of times, about 4 will suffice.
It became my main source of income not by choice or design, but because most of my family are in the building game and have been for decades, and none of them like this type of work and I don't mind it, so whenever any of them get asked to do a job, they give it to me, and I often get repeat buisness from happy customers' relatives, work colleagues, neighbours etc
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