John
wibbled on Sunday 04 April 2010 13:49
Afternoon,
I need to lay a concrete base for a shed.
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.
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).
But if using actual concrete, then these may be of help:
http://www.pavingexpert.com/calcall.htm
For 6x10' at 4" thick, that would be 20 cu ft which is around 0.6m3 (do
check this again!)
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
--
Tim Watts
Managers, politicians and environmentalists: Nature's carbon buffer.