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Posted: Sat Nov 14, 2009 5:13 pm
by dfeather
Hi, I am just in the planning stages for a patio in my garden that will have an overall area of 15msq. In the middle of the area is an old concrete greenhouse base - 8' x 6'. Is it preferable to dig this up and use the same sub base material all round in the prep or can I leave it and put hardcore or similar around it and compact it to a suitable level?
I havent decided on the material to be laid yet so I may have a screed bed or may lay individually dependant upon the flags.
Thanks in anticipation
Dave
Posted: Sat Nov 14, 2009 5:21 pm
by rimexboy
Hi dave welcome
have you got any photos of the area as it depends on levals drainage and things like that, is it only going to be a foot area or will cars be going over it...
the guys on here are a great help but the more info the better
cheers simon 
Posted: Sat Nov 14, 2009 5:40 pm
by dfeather
Thanks for quick reply Simon. Its a level site, the soil around the concrete is soft and I need to dig it out to a suitable depth and intend to compact the sub base well with a wacker.
It will only take foot traffic and that will only be light as its in one corner of the garden where we intend to put a table and chairs on it in the summer. The corner is right angled and has a metre high stone wall running off either side that is newly built.
My intention is to set out a plan with a curved edge running off one wall to the other - half moon shape or similar with tumbled setts set in concrete edging up to the lawn. My thinking here is that this will then mean that any paving laid is tied into a patio area that has firm edges all round. Hope that makes sense!
To be honest something inside is telling me to get the concrete base up and use the same sub base all round. I'm just unsure.
Posted: Sat Nov 14, 2009 6:01 pm
by rimexboy
Hi dave
the more info the better,
the good news is you dont have to dig down loads as its only foot traffic,
have a look at the main site under the paving section that gives you more info.
here is a link th the site index
http://www.pavingexpert.com/pavindex.htm#pp
hope that helps you
cheers simon
Posted: Sun Nov 15, 2009 9:04 am
by seanandruby
You can leave the old sub base in situ and add more around the edges that you dig out. You say it is soft around, so dig out 100 ml and add new sub base to those areas. I am assuming the old stuff is sound?
Posted: Sun Nov 15, 2009 9:24 am
by cookiewales
same as sean if you have enought height for paving on slab leave it there if its not broke dont fix it some pic would be good :p 
Posted: Sun Nov 15, 2009 9:19 pm
by dfeather
Ok, thanks for that guys. I think I will leave it there and add new sub base around it. The concrete base is in good condition so it will take new slabs over it.
Dave
Posted: Sun Nov 15, 2009 9:22 pm
by Tony McC
The niggling worry at the back of your mind is "differential settlement". In essence, if you have part of the new patio laid over a rigid concrete base and part laid over a flexible sub-base, then, over time, the flexible sub-base is likely to experience a greater degree of settlement than the rigid base: ie, there is a difference.
Now, that difference may be just a millimetre or three, or it could be more significant. If this were a driveway or any pavement taking vehicular traffic, I'd definitely break up the base and use all flexible sub-base (or blow the budget and use all rigid base in the form of an extended concrete slab), but as this is just a patio, it comes down to being a judgement call. How firm do you think is the existing sub-grade? Do you expect much settlement, and, if you do, would it be a major catastrophe?
Weigh-up the effort of breaking out the concrete against the risk of having to re-lay part of the patio in a few years time.
Posted: Mon Nov 16, 2009 4:46 am
by seanandruby
I was under the impression that you were breaking the concrete slab up and leaving the sub base in situ. I apologise if there was any confusion. As Tony stated differential settlement would be a problem.
Posted: Mon Nov 16, 2009 8:45 pm
by lutonlagerlout
seanandruby wrote:I was under the impression that you were breaking the concrete slab up and leaving the sub base in situ. I apologise if there was any confusion. As Tony stated differential settlement would be a problem.
4.46 am
sheesh thats an early start sean
LLL :O
Posted: Mon Nov 16, 2009 9:49 pm
by Tony McC
"When I were a lad, we were so poor we had t'get up half an hour before we went t'bed!"
Posted: Wed Nov 18, 2009 8:59 am
by seanandruby
lutonlagerlout wrote:seanandruby wrote:I was under the impression that you were breaking the concrete slab up and leaving the sub base in situ. I apologise if there was any confusion. As Tony stated differential settlement would be a problem.
4.46 am
sheesh thats an early start sean
LLL :O
always up 4.00 mondays for travel to work. In digs rest Of week so lay in till 5.45.... luxury. Lay in today, no need go in till 10 because was at work powerfloating till 2.00 . Love the mornings, calm before the storm, no one about.
Posted: Wed Nov 18, 2009 8:35 pm
by lutonlagerlout
have you got a lap top and wifi sean?
dunno why but i have never got to grips with laptops
i like my comfort zone of up at 7 and 20 minute drive to work for 8, i did 4 years of working in london and getting up at 5 and running 2 miles to the pick up point is no fun in winter especially with your tools
the good old days eh? NOT
LLL
Posted: Wed Nov 18, 2009 9:21 pm
by seanandruby
no laptop with me. Dont know about wifi, not into games etc; is it like a wifee, got one of those.? Just a blackberry to access net.
Posted: Wed Nov 18, 2009 10:59 pm
by lutonlagerlout
a blackberry jeez!!
the wonders of modern technology
i struggled with the vcr remote,then they stopped making them!
is a blackberry like a posh phone then?
i hear politicians use them lots
LLL