Hi All
Have dug out and shuttered for 2 100mm thick shed bases
area 10' x 10' and 10' x 6'
Paving expert site recommends a 6 to 1 mix for bases generally but this is not a big one
I wonder if a weaker mix say 9 to 1 would be adequate as a 30% reduction in the cement cost would be handy
Due to access and having to do it on a sunday this will all be mixed on site
Regards
Would not recommend weakening it as it will become v porous. Ship and happorth tar? chris
With paving slabs on top or not?
If the sand mix is just as a bed for the slabs, 9:1 will be fine to stop it migrating.
If you are putting a shed on the sand, stick with the 6:1...
If the sub-base is well compacted hardcore or stone, and if the eventual appearance of an odd small crack isn't too critical. I'd drop the thickness to 3", but stick with 1:6. For simple wooden sheds used for ordinary domestic purposes, you'd get away with even less thickness than that.
It's easy to over-engineer these things, especially when it's someone else's money.
Don't mix it too wet (strength is a function of water/cement ratio), and compact it well to get rid of air bubbles, then cover it to prevent over-rapid drying out. A layer of polythene under the concrete keeps it wet while it's curing and dry once it's a shed floor, but it does need the sub-base to be blinded with sand, and care while laying the concrete, to avoid puncturing it.
You do know that that's about 1.5m3 of concrete you have to mix? If it were mine, I'd have dug the top inch of grass and soil, then shuttered
3 inches deep, so that the surface was 2 inches above surrounding ground, I'd have saved half a cube of concrete and the end result wouldn't be as at risk of flooding etc. Saying that, the last one I built, a few months ago (for a large wooden wendy house, but the principal is still the same) I just scraped out three channels about 6 inches deep and mixed a fairly strong, dry concrete, this went about 3 inches deep and I laid three rows of bricks on the strips. I then laid paving slabs onto these minature walls, leaving inch gaps between the slabs, underneath being hollow. The end rusult was a free draining solid base, which cost about 20 quid and took 4 hours, given that we used 2nd hand slabs and old bricks.the only visible parts of it are the dwarf wall and the outer edge of the slabs.
thanks for the reples
6:1 it will be and sticking with 100mmRegards
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