Base for granite laying - Concrete st1 or dry ?

[red-star]

I will shortly be ready to lay the 100M2 of granite for driveway, laying on 100mm of concrete with A98 mesh re bar for bad ground this is on 150mm 804. We would be very slow at laying slabs, leveling and so on, is ST1 the bone dry powder concrete? we often see stone layed on this on commercial sites and we would be more confident of this because we can screed the concrete like sand and we would have all day to work with and then water on top of the slabs to set off the concrete???
Do I ask concrete supplier for ST1 or bone dry 4-1??

2nd question I want to lay the stone without gaps or say 5mm, is this ok, the supplier says stone is accurate 40mm deep and 600X300, can I believe this ? and will 5 mm be ok?

I assume I could brush the dry stuff in to close this gap.
Sorry about the repeated innane questions but I have the book, looked at the site ( work of art) but I still need the input from the experts.

[seanandruby]

You need to lay them on a semi dry mix before it goes off. watering a dry mix after you lay them wont give you a consistent bed.5ml joint will be OK, don't butt joint them. you have placed a sound, rigid sub base, don't change to flexi now.

[red-star]

what is the technical term for semi dry mix ??? what do I ask the concrete supplier for, ST1??? How long will the mix be workable for, and can you get a setting retardant as you can with mortar, ie 48 hour mortar.
If the concrete set slow it would take a lot of risk out of job, with no cuts what is the estimate for a good DIY team M2 slab to lay in a day, I was thinking 30M2 which is approx 3 M3 of concrete.

[seanandruby]

Judging by your questions i would advise you to get the materials, mixer and knock it up yourself. that way you can mix what you need. 3 metres of concrete gone off is a lot of hard work.

[red-star]

I do not fancy mixing 10 M3 of concrete, this would be the complete job. I will perhaps go for 2 M3 batches delivered it is more expensive but may avoid disaster.

I have looked at the site re screeding, I have screeded concrete before so I am familiar with the boards ect, I am confused as to the plate compacion of the bed, I assume this only applies to the sand bed and not the moist mix I would use? with the concrete bed shoul I lay 10mm high bed and tap the stone down to the required level?

[seanandruby]

Dont compact with compactor plate. you need to be about 8 ml high and tap down to finished level. if you dont manage to use all the mix then level it out, dont leave it in a heap, or you will need more than a pick next day. go nice and steady and you will be ok.

[Tony McC]

There's a difference between "Dry Mix" and "Semi-dry Mix". Dry mix uses dry aggregates with no added water: semi-dry has minimal water content, usually just enough to bind together the aggregates.

Using the mmodern Euro-bollocks nomenclature, a dry mix would be order as just that: Zero slump. Semi-dry is minimal slump, say around 10mm. Slump is explained here

ST 1 means Standard Mix Type 1, and refers to a weak-ish concrete with an end-strength of around 7.5 Newtons. roughly equivalent to the old 1:3:6. ST 4 = Standard Mix Type 4 = c.20N

The new Euro-bollocks requires you to specify the strength requirement, so ask for 20 Newtons as a minimum.

You can't retard a semi- or dry concrete: not enough water for the chloride to work.

[red-star]

Thanks for all the answers, I have some further questions,
I have laid out the leveling timbers to 10mm above the the position required for the bottom of the stone, and will tamp down to level, we will mix 5 tonne of concrete with small mixer to try out the system before going to the concrete lorry,
we will use moist mix, Question; will the granite not sink on the 100mm bed, it would be ok if all sank at the same rate.

I am thinking of using the 5mm joints but have now decided to lay the granite with no gaps, is this ok?

The notched screeding board is one of the great simple idea's this is so good I am thinking applying for a patent on it!

[seanandruby]

moist mix/semi dry is what you need Red. Tap them down, they wont sink. 5ml joints are recommended to stop them spalling / chipping at the edges. good luck with the patent, its a wonder none of us brewers had thought of it :laugh: :laugh:

[lutonlagerlout]

never heard of that one?
notched screeding board??
it'll never catch on
LLL

[haggistini]

if you cover your area with concrete leaving your slab depth and allow for say 30mm of screed then all you need to do is order the screed you want for that day!! this should be ok for heavy traffic if they are compacted well . just make sure you keep off them for as long as you can and use a timber to step on your last row to aid laying them...String line your slabs in add an extra 5mm for gap and always work to the front line as granite will have different widths ....well thats what i do and we order 24hour retarded screed if we got to do a saturday..what do you think forum???
haggis!

p.s. then dust up with kiln sand !!

[Tony McC]

Buying-in laying course material is all well and good if you're familiar with concrete/mortar, and you've got a big enough area, but the vast majority of jobs still rely on site-mixed materials. Pre-mixed laying (and jointing) materials are more popular on commercial projects, as they remove the risk of varying strengths between mixes.

Not sure about using KDS as a jointing material when the paving has been laid on a cement-bound bed, though. I'd have opted for a cementitious (or resinous) jointing.

[red-star]

I am still thinking that it would be easier without the joints of 5mm I saw an area laid like this at the granite suppliers and it looks good no chipping of edges, like all beginers it is bad enough laying the slabs without the backbreaking job of jointing.
Is there any problem with expansion, main standing area is approx 9X9 mtrs do I need to use an expansion stirp??

[seanandruby]

The 5ml is a recommendation only, its up to you to incorporate it in your slab. you probably seen a trial area at the suppliers that hadn't been trafficked. as the man said " suck it and see" no need for expansion strip.

[lutonlagerlout]

butt joint in haste, repent at leisure,red star

sean knows the craic,and the craic is that nothing is as square as it looks

5mm all the way

LLL