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Posted: Tue Mar 11, 2014 2:07 pm
by Chui
Which is best for laying a patio, with flagstones, on clay soil? Concrete or aggregate and sand? I've had different views/quotes from landscapers. One said he would use mot type 1 on top of a geotextile membrane, compact that, then lay sand and compact that. The other said he would lay 2" to 3" of concrete and lay the flagstones with dabs of concrete & sand on top of that. They came out about the same price.
The clay tends to be heavy and wet here.
Posted: Tue Mar 11, 2014 5:43 pm
by lutonlagerlout
the pair of them are noddys
100mm type 1 compacted
30-60mm of bedding (sand cement and water mixed)
then the flags
laying on neat sand is a huge fail
dabbing is a complete fail
so on this premise both are wrong
LLL
Posted: Tue Mar 11, 2014 5:51 pm
by KLS
Second what LLL says.
Posted: Tue Mar 11, 2014 6:01 pm
by msh paving
I will third LLL
thats the way it should be done MSH 
Posted: Tue Mar 11, 2014 6:17 pm
by Chui
thanks for that. Would the concrete option work as long as he puts more than just the 5 dabs of cement under the flagstones? The reason given for concrete is that with the soil/clay round here moves too much.
Posted: Tue Mar 11, 2014 7:16 pm
by Chui
Also, with the sand/cement option, is it enough to have the flags laid tight fitting then sand brushed over to fill any gaps?
Posted: Tue Mar 11, 2014 9:12 pm
by r896neo
Small format pressed concrete flags such as 400mmx400mm or smaller can be laid on a compacted screeded sand bed. They also can be tight jointed with kiln dried sand.
Any wet cast concrete, natural stone or larger flag needs to be laid as LLL has said.
Laying flags on a full bed of concrete is difficult and unnecessary.
Sand jointing is only possible with man made flags so as to get a consistant joint. its only really used in flexible construction when laid on only sand like block paving. Using a sand joint on a rigid bed such as mortar can give problems as it never drains.
Posted: Wed Mar 12, 2014 9:55 am
by Tony McC
If only there was a website somewhere that had all this sort of information written out and illustrated! 
Posted: Wed Mar 12, 2014 10:18 am
by Chui
My apologies..for my query as to whether brushing sand between tightly butted flagstones is enough ...when I said sand/cement option I meant the method LLL said, ie sand mixed with cement on top of type 1 compacted. SO my question should probably have read "Also, when laying flagstones on top of sand & cement bedding, which is on top of compacted type 1, is it enough to have the flags laid tight fitting then sand brushed over to fill any gaps?" 600mm x 600mm has been mentioned by one of the landscapers.
Also apologies to Tony for my obviously having missed the answers somewhere in this site! I have been searching, honestly! Obviously just not enough.
The reason for my initial query was that the guy proposing a cement base said that the area where I live, with heavy clay, requires it. That other patios done with the traditional method don't survive around here. My own research online found that concrete can be best for certain conditions but I don't know if my small damp clay garden comes under that. If it wasnt for the clay argument I'd already have booked the guy doing the standard, non concrete method. The concrete guy has confused me!
Posted: Wed Mar 12, 2014 5:41 pm
by r896neo
There are some occasions when a concrete sub-base would be preferably depending on site conditions but to actually bed the flags on concrete is unusual.
Some people would do it on driveways for extra strength but I think that is probably because they think it will be stronger. Whether it actually makes a difference is a technical question for someone with more brains than me.
Heave and other ground problems associated with clay should affect the sub-base and sub grade preperation but shouldn't have a bearing on the bedding layer. In my laymans opinion. I welcome correction from a boffin.
Posted: Wed Mar 12, 2014 6:01 pm
by GB_Groundworks
It'd have to be a properly constructed reinforced raft to stand upto the alleged potential movement anyway 2"-3" of lean mix knock up by said Cow boy isn't going to do anything if you get clay heavy.
As per main site 100mm compacted mot then the paving laid on a full bed of sharp/grit/river sand (not fine builders sand) will be fine.
In all honesty don't employ these two find someone who actually knows wgat they are doing!
