Shed base

You want a concrete base not a mortar one.
Sand and cement make mortar which will not be strong enough.
The simplest concrete is with mixed ballast (sand and stone)
Do a 6-1 mix. 6 ballast to 1 cement (by volume)

 

an average bag of ballast holds about 1/60 th of a cubic metre. work out your base size in metric. times the width by the length by the base and youve got the cubic capacity. I never take account of the cement in the calculation of how much i need. I always work out how many bags of ballast i need then divide the total by six to get the 1:6 mix

 

The cement wont pay any part in the final volume.
Use 1 cubic metre of ballast and you will have 1 cubic metres of concrete.
14'x10' will need 70 cubic feet at 6" depth (1.98cu metres)
So you will need 2 cubic metres of ballast for the concrete plus whatever you use for the hardcore.
Rubble used for the hardcore will have voids that need filling up. Ballast will do this although I prefere skalpings because it forms a firmer base.
For a shed I'd work on 9-12" of hardcore and 6-9" of concrete.
I used over 18" of rubble & skalpings for my garage because the garden was raised and needed drainage which the hardcore formed part of.

 

Dewy, that's one base you got! Great if you got hardcore to bury, not so good if you're buying it (agree preferably scalpings, compacted down) in.

I'm sure the advice so far will produce a base of astonishing strength (suitable for vehicular use) but for a shed base you'll find 2-3" of scalpings and 2-3" of concrete will fit the bill if you're looking to keep the costs down.

Given the dodgy weather, another piece of advice (from mixamate website) is that regardless of the weather, wet concrete should be covered in plastic sheeting and allowed to dry slowly over 2-3 days.

 

The hardcore I used under the skalpings came from a concrete path that ran through the middle of the base and a visit to an adult training centre that was being demolished.
The demolishion boss was glad to find someone to take away some of the rubble.
I wish I had some way of transporting the large roof & floor timbers they had.
Thousands of feet went on a fire on the site.

 

concrete for 14ft x 10ft at 4" 1.71 cubic yards at 5" 2.18 at 6" 2.59
any old rubble for hardcore but if you have access to a trailer try and get inch and a half down.(roadstone/maintenance)

 

B.T.W. one cubic metre of ballasat does not equate to one cubic metre of concrete. I have a mixer that takes a bag and a half of cement and 35 shovels of ballast which produces two barrows of concrete, and I can not get 35 shovels into two barrows.

 

I am also thinking of putting up a shed and was intending to use 2x2 slabs (Bro In Law gives old ones away) but wondered should I lay down a concrete base instead?

 

An alternative suggestion is to use old railway sleepers for the base. They are not likely to rot as they are covered in creosote and they spread the load nicely. A lot cheaper than a concrete base and gives good ventialtion under the floor.

I used this for some decking and it has been very successful.

 

Hi,
I have just been through the same. I have just laid foundations and base slab for my conservatory. I used a 1:5 mix of cement and ballast (stones and sharp sand mixed). We used 10 shovels of ballast and half a bucket (about 1/3rd of a 25kg bag) of cement, this was nice and simple and easy to chuck in the mixer. I was recommended by a builder who successfully also told my mate how to calculate his volumes that you need roughly 1.7 tons of ballast to get 1 cubic metre of concrete. This sounds strange until you realise that ballast is around 950 kg per cubic metre and concrete is 2200 ish! I have just laid a slab at 1:5 which was just short of 3x4 metres x about 125mm thick (1.5 cubic metres) and this used 3 tons of ballast with about a barrow full left over. My foundation was about the same volume and I had about 2 buckets full left out of 3 tons - cutting it a bit fine!!
I also used between 14-15 bags of cement for this.
Please make sure you have enough and perhaps a bit more as you cannot leave it halfway through. I would go for 2 tons per cubic metre which will account for the ballast being measured when wet, an over exuberant shoveller and the fact your nicely measured and calculated sizes will not be as dug as a spade tends to wander!!! You can always use up the spare. Be careful with the water also as a tiny drop more when a bit stodgy will suddenly make it very wet and runny.
Hope this helps. Mail again if not sure.

 

Can I just summarise and make sure I have this down right?

I want a metal 10x8 shed with a 3 inch base (according to mfr, shed is from Screwfix catalogue). Thats only 0.54m3 of concrete. Under that I have need (???) a similar amount of compacted scalpings?

To lay the thing I dig my hole, compact the soil when level and put shuttering to a depth of 6 inches (if thats my scalpings and concrete depth) with pegs holding it from the outside. Then to level the resulting concrete just tamp it down and make sure its level with top of shuttering?

Never done it before!