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Posted: Thu Jul 05, 2012 3:02 pm
by gippeswyc
Very useful site this is, thanks guys. Question I have not been able to find. I have 20 sq metres of patio to lay in an L shape. I think a sharp sand/cement mix of 10:1 will do the job but once the cement is added what is the working time before it starts to set?
My base mix will be around 30mm. Would I best to do the job in sections, another reason being I have 2 drain covers to negotiate which will slow things down. I would rather do the job over 2-3 days than rush around worrying about my base hardening. Thanks
Posted: Thu Jul 05, 2012 4:30 pm
by Pablo
10:1 is only used on on large or butt jointed flags that are laid on a pre screeded bed depending on what you're doing I'd recommend tightening it up to 5:1 and make it by the barrow load so you've no wastage. A load will stay usable for a few hours but you'll have it used in minutes.
Posted: Thu Jul 05, 2012 5:08 pm
by Carberry
Pablo wrote:10:1 is only used on on large or butt jointed flags that are laid on a pre screeded bed depending on what you're doing I'd recommend tightening it up to 5:1 and make it by the barrow load so you've no wastage. A load will stay usable for a few hours but you'll have it used in minutes.
And will only cost you an extra £20 in cement.
Posted: Thu Jul 05, 2012 5:43 pm
by haggistini
Stay off them for a day atleast! or use boards to cross over them to spread the weight if you have to 5:1 is much better than 10:1
Posted: Thu Jul 05, 2012 9:42 pm
by lutonlagerlout
10:1 is a noddy mix
all the fellas on here use around 6-5:1
which equates to half a bag of cement and around 10 shovels of sand
30mm thick is very tight unless your subbase is perfect
LLL
Posted: Thu Jul 05, 2012 10:10 pm
by k13wjd
i went a tad nuts with the mix, more like 3:1. that said, it didnt cost that much, £25 in cement, £30 in sand. some parts are 80mm thick 
. stuff is rock solid, it'll out last my fecking house !
Posted: Fri Jul 06, 2012 7:15 pm
by Tony McC
lutonlagerlout wrote:10:1 is a noddy mix
Is it eck a Noddy mix! It's fine for patios, if you know what you're doing.
With no heavy loading, it's only necessary to bind the aggregate so that it 'sticks' together and hardens. When laying road kerbs, we'd often use a C7.5 concrete, which is roughly equivalent to the old 1:3:6 mix, which is....errr.....9:1.
If 9:1 is satisfactory for kerbs, then 10:1 should be more than adequate for a patio.
The reason why stronger mixes, such as 4:1, get used is to improved adhesion, but there are better ways of doing that instead of relying on excessive cement content.
Posted: Fri Jul 06, 2012 11:01 pm
by mickg
>>>Is it eck a Noddy mix
it is if you need access over the paving you laid the previous day and its still soft the morning and a flag get disturbed all for the sake of an extra spade of cement - does not bare thinking about to be honest
your just a tad older than I am tony and in days of old I was taught it was always 4:1 for brickwork and 3:1 for rendering or for laying quarry tiles into a sand and cement screed which is pre adhesive days
they brought out light weight thermolite blocks and they started to crack due to the mortar mix being stronger than the block hence the weaker mixes of 6:1 or 8:1 but I have never heard of any mix to bed or lay any product being as weak as a 10:1 mix until I joined paving expert
I am not trying to open a can of worms with the modern day technical side all I am saying is that's what worked for years and years without any problems and I would never promote a 10:1 mix for anything other than filling a cavity as in my opinion its too weak a mixture and takes much longer to go hard enough to take any traffic
when we need to remove the top 60mm - 70mm of the concrete haunching from the back of existing edging or kerbs on driveways on new estates you can see its a strong mix as the concrete is a blue/green colour which correct me if I am wrong that's normally seen within a C40 mix and its rock hard too
Posted: Fri Jul 06, 2012 11:42 pm
by Brucieboy
mick - the reason the concrete is blue/green is because it's made with a blended cement containing ggbs (ground granulated blastfurnace slag), i.e. CIIIA. The blue/green comes from the iron/manganese sulphides in the ggbs. It disappears when the concrete is exposed to air after a couple of days.
Posted: Sat Jul 07, 2012 7:04 am
by mickg
thank you Bruce, its much harder than normal concrete though we have to use a breaker to chip off the top as using the chisel and lump hammer you get no where, or put it this way its much harder than a 10:1 mix of semi dry concrete used to back kerbs would be
Posted: Sat Jul 07, 2012 7:42 am
by lutonlagerlout
I will never be convinced of a 10:1 mix 
I have taken up patios where the previous layer used a weak mix and ants and all sorts of invertebrates have tunneled into the leanmix and weakened the patio
road kerbs by their nature are much heavier than a 38mm flags and tend to be haunched with stronger gear and have bitmac at the front
I have worked with blokes who used to scrimp on cement and it made no sense then, and it makes no sense now
I know technically i may be wrong but for an extra £30 on a patio it works for me
LLL
Posted: Sat Jul 07, 2012 7:57 am
by seanandruby
I go with the Cappo de Cappo on this, using just enough cement to bind the bedding. Mick when you lay a patio without cement, you can walk on it straight away, in fact laying council greys you need to stand on the previous laid slab. the combined weight of a 65ml 3 b 2 and the flagger doesn't sink the one you are standing on m8, and joe public walking on them as you go.. Laid thousands when we used to just mix in a bit of lime in the good ole days. As Tony said ''if you know what your doing.'' :;):
Posted: Sat Jul 07, 2012 9:42 am
by mickg
In my opinion laying 20mm sawn stone or granite requires a different bed to a council grey which as you say was laid on ash years ago then grit/course sand without any cement
following manufacturers laying procedures for these thin products which is what we mainly lay they recommend cement added to the mix but never recommend a weak 10:1
Always eager to learn though Sean Even at my age cos maybe just maybe the old school Irish guys who taught me were wrong ???
Posted: Sat Jul 07, 2012 9:51 am
by Bob_A
Tony McC wrote:lutonlagerlout wrote:10:1 is a noddy mix
Is it eck a Noddy mix! It's fine for patios, if you know what you're doing.
With no heavy loading, it's only necessary to bind the aggregate so that it 'sticks' together and hardens. When laying road kerbs, we'd often use a C7.5 concrete, which is roughly equivalent to the old 1:3:6 mix, which is....errr.....9:1.
If 9:1 is satisfactory for kerbs, then 10:1 should be more than adequate for a patio.
The reason why stronger mixes, such as 4:1, get used is to improved adhesion, but there are better ways of doing that instead of relying on excessive cement content.
I've often wondered why their has been a difference of opinion between Tony's book/website quoting 10:1 and many of the other regulars prefering a stronger mix.
I'm a DIYer so if Tony says 10:1 then I'm sure he knows what he is talking about.
I can't remember the exact mix but mine was definitely stronger I can't compare that to a weaker mix 'cos I've never used one.
If I was to do another patio I'd use a stronger wet (not too wet) mix, not because I think it's correct but with my limited experience I reckon it's easier to work with.
Posted: Sat Jul 07, 2012 10:04 am
by Tony McC
If a 10:1 mix hasn't hardened sufficiently overnight to bear the weight of someone carefully walking across the surface, then either the cement is perished, the ambient temp has been too low, or someone needs to lose a lot of weight!
4:1 or 3:1 for brickwork is fine, and that's the correct mix for pointing paving, but for th bedding of a simple patio, there's no justification whatosever for all that extra cement. What is it acheiving? The paving is not intended to carry the sort of loads that warrant a 4:1 mix. We'd happily use that stronmg a mix on, say, a town centre pedestrian area where they have mechanised sweepers and god knows what else running over the surface, but for a patio? Naaah!
However, if anyone wants to work with cement-rich bedding, and cope with the problems that can bring, such as additional eff or the salts that migrate through the incredibly porous Indian sandstones, they are welcome to do so. It's not necessarily wrong; just wasteful.