[TheCaptain]

Right, I've got a load of concrete to lay when I get a break in the weather and need some advice regarding expansion strips and materials as I'm having a right 'to-do' with my cantankerous old git of a father in law.

All the framework is done, and dug out to 4 inches. Is this sufficient?

I'll need an expansion strip at the 12ft mark (it's a thin strip , 3m wide, 14 long) what's best for this?

It's being laid next to concrete that's been down for years. Do I need to put anything down between the old and new?

[Fowgill Farm]

Being a builders OH i would say four inches wasn't deep enough but it depends what the floor will be used for, if you're taking machinery over it it will just break up that thin a layer. Most of our floors are six inches deep minimum some in the big shed deeper (9") with plastic liner (DPC) and reinforcing steel grids and then ready mix on top. The first batch we put in for our shed floor was awful and we had to have Lafarge technical support out to see it and they agreed mix had been incorrect and they paid to have it removed and replaced! so even the professionals get it wrong sometimes.
Can't help on your other queries i'm afraid, but nearly everyone has a mate who's a builder and i would ask around, better make a good job of it now than have to go to the expense of having to dig the bugger up again and re-do when its all cracked up.
Mandy 

[lachlanandmarcus]

Dont do any with home mixed stuff - our stables ramp cracked up after a year. The proper concrete lorry stuff is essential. If animals are to use it you can get anti urine additive, and also if you are anywhere cold you can get fibres added which help to stop it cracking up in the cold.
If you need drainage channels/covers I recommend Hauraton ones, cast iron, expensive but rated for lorries etc going over them. The thin (wafer thin) shiny pale grey clip in things are a death trap, so sharp when they ping out (and they will!)
 

[robert waddell]

concrete is a mine field for the inexperienced       there are different quality's of concrete  from low strength to high strength and it is all to do with the cement content    cheap concrete is for footings and haunching high cement content is for Resistance to salt and silage effluent
4 inches if it is light traffic and has fibres in it     steel and fibres effectively double the depth of the concrete
a vibrating screed is essential to get a good Finnish  and don't forget concrete is a very heavy item to shovel  also if it is to dry you will never move it and concrete goes of quick      and there is nothing wrong with home mix   as long as you get the quantity's right  IE the cement content      then there is the curring that has to be done right or it will crack    and not forgetting DONT GET IT ON YOURSELF or you will get chemical burns      wear wellies and don't kneel in it or get it on your eyes or hands
have fun

[TheCaptain]

We're going off what's already laid, it's our stable yard so only light traffic really. It'll be ready mix out of a truck because it's 6m cubic, but we're going for R32 mix or whatever it's called...

[chrismahon]

Presume you have hardcore under that planned concrete slab Captain. I also think 4" is too shallow. I put 6" medium strength and a steel mesh in 3" down for my sectional concrete garage to sit on. Got some splashes on my jeans and got burned by it! Mix for with steel reinforcement is different to without as the alkalinity needs to be very high to stop the steel corroding.

[lachlanandmarcus]

For our stable yard building regs made us build it like an aircraft apron, its mega - turned into a civil engineering project. Ironic really cos the main house has no foundations at all.....

[bazzais]

For such a small area its worth spending the extra - specially if your having it delivered - 2 batches should do it if you have the access for full sized loads.

I'd put 4 inches down for a shed thats not got heavy traffic over it - but if its for a yard or trackway you will need more - or have a really good base as someone mentioned.

[goosepimple]

Yup, go for 150mm (6inches) and put either a timber strip or a flat metal bar between the old and the new.  Make sure you have hardcore down with sand or ash on it to make it smooth, get a damp proof membrane (some plastic) down on top of that with enough around the edges to lap it upways by about 150mm and as much rigid insulation as you can depthwise (at least 100mm/4inches) which will stop the cracking.  Dont know how far you have dug down - you may have to dig deeper than you think in order to get in the sandwich on top. 
Must be a youtube to give you visuals.  Make sure you have ordered enough concrete and that if you've ordered too much you have somewhere for it to go - and good luck 

[oor wullie]

I just poured a similar slab (two 3m x 12m slabs next to each other to give a 6x12m slab for a shed).  Not having done anything like this before I went to the builders merchant and asked what I should use for an expansion joint.

I ended up with a roll of firm plastic foam which I fixed along the edge of the first slab just prior to pouring the second.  The upper 10mm of the foam stuff is detachable along perforations so my next job is to remove this bit to leave a 10mm channel along the join.  This channel will then get filled with some kind of extra tough sealant to leave a smooth join on the floor.

Sorry but I have no idea what the stuff was called.

Tim