I've got to lay a 3m x 2.5m concrete slab to put a log cabin on.

I've been told to make it 6 inch thick and get some steel re-enforcing mesh as well.

So the question is, how much balast and cement do I order from Wickes?

And inside the area there is a small 6 foot square area of slab already there, is it ok to leave it (it's 6 inch thick) or do I need to get rid and lay fresh.

Always a good start... Metric x metric x imperial....

Firstly, you need 1.2 cu metres of concrete to give a bit for wastage. I wouldn't even bother trying to do this by hand, as it needs to set as a whole mass and it will take you a good couple of hours to mix. Can you not get a readymix delivery to where you want it..? That quantity would only be about £100 ish plus vat round here.

If you did still want to do it yourself, the quantity would be 2t of all in one ballast and 15 bags cement. Dont forget you will also need a dpc under the concrete and the base built up with roadstone or hardcore and blinded with sand before you start...

Reinforcing isn't really needed on something that small - it would cause you more hassle than its worth

Cheers

Pete

Jasper,

If you're feeling lazy and don't want to make a mess get premix poured in, much quicker and easier

I'd leave the old bit in situ unless it affects putting the mesh in. I put a ton or two of type 1 down to stabilise the ground and compacted it with a wacka plate before putting my base on top for the garage.

Ned.

but that is 2.5x3x.15 which is 1.125m3 at about 2 tons a cubic metre plus water. If you can lay on top of the slabbed area just bury it and it will be twice as thick, it's not going anywhere.

Ready mix - now that does sound like a good idea.

So exactly how do I need to prepare the base? I thought I could just dig down to 6 inch and then pour the concrete on top of that ... obviously not!

Depends what you're building on.... e.g. if you're building on solid granite you don't need to do much. If you're building on top of soil that is 99% deep you might need to put in some hard core? Most of the time using a vibrator plate to impact the stuff underneath the log cabin will be a good idea...

Ive only got experiance with founds rather than a slab. i had to dig down to clay. Then pour required thickness of concrete with correct steel mesh (as requested by building officer via building regs approval etc). Ii is therefore possible that you have to gig down 2 or 3 feet to find the clay. 6 or 9" of concrete back in then bring up the height with trench blocks (like concrete blocks but a certain strength), then you can lay floors etc.


I would have thought a concrete slab needs to be floated on a suitable base as well. Will you only need one lot of mesh or a couple correctly spaced (maybe im getting confused with floating floors etc).

OK

Very quickly....

Dig down to 300mm below finished floor level (and assume you are going to add min 75mm above existing slab)

Fill hole with MOT1 or other graded hardcore and compact with plate vibrator.

Blind with sand (i.e. cover with sand to stop sharp stones coming through) and compact again.

Shutter in edges to give a decent edge to level off - scaffold boards are good for this...!

DPC over area, and make sure it overlaps the shuttering.

Pour lots of readymix into the hole, tamp with a board and get it nice and level.

If you need any further info try Paving Expert

Cheers

Pete

Place DPC over entire are

When putting steel mesh in make sure it sits about 40mm above the ground level (spacers). You COULD do it with electric mixer for Lowcost as long as it was all done in the one day and therefore Homogenous...........I did

Alex

Thanks chaps - very useful....

Definitely readymix, or in my case spotmix.

I'm famously tight and started doing it myself before realising it was a stupid idea.

And if the guys who come round your way are the same as here, they will invoice you for less than you ordered and split the difference with you.

Every little helps.

Our concrete for the garage base was in within 30 minutes. The small bit I did myself took around 4 hours and was a pain in the sphericals.

If you're near Soton / Portsmouth I found Covers to be the cheapest for ballast / cement when doing my conservatory. Don't use Elliots you'll get shafted.

Shop around for the ready mix -- make it clear you cab in pay in CASH.

A lot of the smaller Ready-Mix outfits will supply the reinforcing included in the price --- but it is overkill for such small slab