potential shed disaster awaiting

[john westmore_______]

Our old wooden shed was crumbling so we knocked it down and have broken up the existing concrete slab and now have a 'Yardmaster' tin shed on its way this week. The new base is to be 2,70 metres by 3,38 metres.

If you go to this tinypic website you can see the photo of where we are at:

two front timbers are laid level, the back edge on the left goes up to concrete gavel boards on to a fence and the back edge on the right goes up to a wooden fence. The boards for the concrete at the two back edges have yet to be put up. The two front edges in the picture have two layers of old bricks loosely placed in to fill up the space and to bring the height up. We are in north London, mill hill area and the soil underneath is good loam up to a depth of a foot or so, then rests on clay.

Now here's the problem. Being novices my son and I have had to consult various people. Some say get a mixture of about six or seven bags of builders soft sand, mixed up at six to one with cement lay level it off and then put down (some 50 in number?) concrete 450mm square slabs.

Another person has said to get six bags of ballast from Wickes mixed with cement in a five to one ratio, plus 1.5 litres of water for every bag of ballast. Tamp it down on the top and put the shed on top of it when dry. They also said to get it all the concrete down and mixed within a two hour time frame we should have at least two or three fit people, whereas there is only my son and me who is sixty five so not so fit.

Would anyone know of any book on this, or be able to directly advise here the *simplest* satisfactory way for a couple of novices please to get this shed up on some kind of foundation? Thanks for any advice.

[Vortex3]

You're lookting at approx 9 sq. m, and - say 50mm thick. That is about 0.5 cu.m of Concrete needed.

I reckon you need one jumbo bag of Ballast (if it can be easlity delivered to the location and 5/6 bags of cement. Unless you can beg/steal/borrow a mixer then that's a lot of hassle.

What about one of those companies that will mix on the back of a truck and deliver by the wheelbarrow?

[stuart noble]

Good advice but I think I might delay the delivery date until the base is done and firm enough to work on.

[The Medway Handyman]

Loads of info here

kind of floor does this metal shed have?

[Andrew Mawson]

edges have

height up. We

consult

Do NOT use soft sand for concrete, use sharp sand. Soft builders sand has rounded grains that make for a much weaker concrete. Buy ballast and ordinary portland cement. 1 bag of cement to 20-24 shovels of 20mm ballast.

AWEM

[meow2222]

That's 3-4" depth of mortar in total, so no saving over a poured concrete base. I dont see much sense putting slabs down when you can just pour more concrete and get a better result. If you're doing a poured base, the mix should contain stone as well as sand. If you were going for a slab base, 2" of mortar isnt usually needed - with the mess you've got it would be, but why slab when you can just continue to pour.

short version is in your case I'd definitely go with a poured base. 1:3:5 would do nicely, though you could use weaker if preferred.

NT

[Pete Verdon]

If it's anything like my Yardmaster, there will be no floor. The bottom frame simply bolts down to the concrete base. Works fine structurally, but I did have a problem with damp coming up through the concrete and causing condensation (I've since put down a plastic membrane covered with OSB which does the job).

Pete

[Pete Verdon]

My Yardmaster shed is on (preexisting) slabs. Given the choice, I'd recommend straight concrete - the unevenness of slabs makes it harder to prevent water running under the base rail and into the shed.

Pete

[meow2222]

Sharp sand concrete can be made stronger, but I dont think theres any DIY application where the difference is significant. It does matter for roads & bridges.

NT

[Andrew Mawson]

Sharp sand concrete can be made stronger, but I dont think theres any DIY application where the difference is significant. It does matter for roads & bridges.

NT

Having broken up 30 cu yards of various bits of concrete previously laid in a barn as a grotty floor I can assure you concrete made from soft sand is definately much weaker - they'd obviously used up what was to hand, and the bits made from yellow builders sand were like butter compared with the grey bits made from sharp sand.

AWEM