Concrete slab for wooden garden office

I'm getting a small garden office built - mostly built from wood, but pretty solid - total weight somewhere around 1.5 tonnes over a 3.2 x 2.2m area.

The company putting it in say it can rest on paving slabs, but that a concrete slab is better. They recommend a depth of 10-15cm.

I'm new to this, and on trying to order readymix concrete, the plot thickens (sorry...). Do I want C15, C20 or C30? What 'slump' do I want? Do I want polythene fibres mixed in with it?

People on the phone at each company I've rung have been helpful enough in their own right, but often contradict what I've just been told elsewhere, etc.

I've had quotes varying from £170 to £270 for the same quantity (1.3 m3) delivered - quite a variation.

How much hardcore should I aim to have under the slab? The ground is already well compacted soil. I've also been advised it's worth mixing some bits of metal etc in with the slab to reenforce it - comments?

Sorry to ask so many questions in one go. Just any comments or suggestions really... Thanks.

you will need a 100mm thick concrete slab. i would have thought reinforcing mesh was over egging it slightly.
dig out 200 - 250mm of soil and fill to within 125mm of finished level using mot stone. this will need compacting. lay out and peg or pack shutter boards.

blind the stone with sand and lay 1200 gauge polythene, turning polythene up the sides.

pour in concrete and tamp well to levels.

trowel concrete a few hours later.

i would be inclined to mix my own at this quantity. the materials will cost less than £100 but you will need to beg/borrow/hire a mixer for the day.

if access is simple and the readymix can be shot straight in then i may consider readymix, but not at £270.

tell the boys at the r'mix plant it is for a floor slab. decide how wet you want it when the wagon arrives. no need for fibres.

c20 will do and 70 slump will make it easier to tramp level.

Thanks for the tips.

marshman said:

c20 will do and 70 slump will make it easier to tramp level.

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tramp

noseall said:

marshman said:

c20 will do and 70 slump will make it easier to tramp level.

Click to expand...

tramp

Click to expand...

That your passport photo eh Nose?

oooh that's a harsh comment deluks!

You know noseall's bigger, cleaner, more intelligent, better looking brother liked his special brew !!