Afternoon,
I need to lay a concrete base for a shed. I recall needing a mixture of ballast and cement, but need help in
a) what ratio to mix the cement to ballast b) how much ballast and cement to order.
The shed size will be 10ft x 6ft.
I'm asuming the base will be around 6 inches deep (unless you guys advise otherwise).
Thanks, John
John wibbled on Sunday 04 April 2010 13:49
If it's only a shed (rather than a heavy duty workshop) you could make life easier and lay paving slabs on sand and optionally the sand on compacted hardcore or Type 1 MOT (the latter would be better being whacked down with a plate whacker, cheap to hire) Build a wooden frame around the perimeter to set the levels, take off the loose soil and dig out if required to the right depth, add hardcore (if using) and tamp/whack in. Add sand, tamp or whack down and adjust finish level with a 7-8' tamping bar down to the level of the wooden sidings.
Pave.
A long time ago, I did a shed on paving slabs on 2" sand with a little cement added dry (about 1:10 - very weak) on soild with the top scraped off mostly level. Left the wooden sides in, paved and watered in to start the cement setting. Just enough cement to help stabilise the sand. Waited a week then erected shed. It was happy for years so that's a measure of what you
*can* get away with. You just make some value judgements about the state of the ground.
But if using actual concrete, then these may be of help:
If you're bothering to mix concrete, might as well go straight to a C20 which is a good strong general purpose mix ideal for slabs. The calculator on that page says, rounded a bit
8 bags (25kg) cement 400kg sand 700kg gravel 180l of water. 400kg sand and 700kg gravel sounds a little more than a ton bag of ballast (which can mean anything from 800kg to 1000kg), so that would be a convenient measure, perhaps running the slab a little thinner and a bag less of cement.HTH
Tim
Why concrete? A layer of slabs on a light mortar base would be far easier to lay, as well as being very easy to take up if you ever want to move the shed.
6" deep? How many tons are you expecting the shed to weigh? I'd say a 3" layer of cement would be sufficient for any garden shed, if the sub surface has been flattened/compacted.Rough calcualtion - 10'x6' = 6 sq. M. , x 75mm depth = .45 cu M. x 150depth = .9 sq. M. A bulk bag of ballast will be roughly 850kgs (they are a nominal 1 tonne, but dont come very close IME.) A bulk bag is roughly .75 Cu.M A 10-1 mix would be fine for a shed I'd say, though for a harder surface go to 6-1. So at 10-1, you need 85kg of cement, at 6-1, 140kg to mix with 850kg of ballast.
850kg would give a depth of 4 to 5 inches.Alan.
replying to John, Darren wrote: How much hardcore & sand do I need for 8/6 shed
I wish you folks would use the correct newsreaders instead of the mickey mouse on at home owners club that messes up dates and leaves pictures elsewhere. Brian
What are you laying, a 4" base? Dried out masonry has a density of 2.2, and 3:1 should work good, so it can be calculated from there.
8'= 2.4m 6' = 1.8m 4" = 0.1m 2.4 x 1.6 x 0.1 = 0.384 cu m x2.2 gets you 0.845 tonnes.NT
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