Sanity Check on Cement / Ballast for Concrete

[Skavenger]

Hi;

I am trying to work out cement / ballast materials to mix up for some footings for my small 3 x 2 workshop project as well as mortar requirements for the walls.

The workshop floor space is a an irregular quadrilateral shape 3m x 2m x 2.5m x 1m.
For the wall footings I have rounded it up as 3 + 2 + 3 + 1 = 9m.
The wall footings will be 300mm (0.3m) deep and 100mm (0.1m) wide x 9m long.
The floor space will be approx 3m x 2m with footings 100mm (0.1m) deep on 150mm hardcore.

According to an online calculator here the wall footings work out to be 0.3m3 and the floor footings to be 0.6m3 totalling 0.9m3.

According to another online calculator here this would equate to a total of:
11 x 25kg bags of Portland Cement
2 Tonnes of Ballast

Which is about £160 from Travis Perkins assuming that there bulk bags of ballast are 1Tonne (it does not say)
Would this sound correct?

The base structure of the workshop will be made up of breeze blocks, the rear and side walls are already in place (part of an earlier structure) so I need to build up the front wall (about 3m) and one side wall (about 1.5m) up to four - five breeze blocks high.

According to this calculator I reckon I will need:
2 x 25kg bags of Portland Cement
4 x 25kg bags of sand (Seems a little light?)

Many thanks

 

[Ian H]

I think the bulk Bag are more like 800kg's

 

[SFK]

Skavenger
Mortar ratio is normally 5:1 for outside above ground walls and 3:1 for below ground walls, so the following looks incorrect:
- 2 x 25kg bags of Portland Cement + 4 x 25kg bags of sand
as this comes to 1:2 (very strong mix)
If you get 2 x 25kg bags of Portland Cement you need 10 x 25kg bags of sand to get the 5:1 ratio, or
If you get 2 x 25kg bags of Portland Cement you need 6 x 25kg bags of sand to get the 3:1 ratio.

And agree with IanH that a bag of Ballast is about 850kg.
sfk

 

[oldbutnotdead]

And of course you can mix a cubic metre with a mixer (ideally you'd have 2 on the job, one mixing and one barrowing and puddling). But if you've got access (even pedestrian access to the back garden), for the price you quoted you should be able to get readymix barrowed in. Which will be a whole lot faster and easier on your back

 

[Skavenger]

And of course you can mix a cubic metre with a mixer (ideally you'd have 2 on the job, one mixing and one barrowing and puddling). But if you've got access (even pedestrian access to the back garden), for the price you quoted you should be able to get readymix barrowed in. Which will be a whole lot faster and easier on your back

Thanks for the advice - yeh I thought the mortar ratios were wrong!

Ref ready mix v self mix, I may be able to borrow a mixer from a neighbour (if it works) but Jewsons will hire for a week for £28.
Didn't think you could get ready mixed in such small quantities but how would I be able to lay the footings and the floor base (less scree coat) at the same time?
I would need 0.3 cubic meters for the wall footings which then needs two days to cure, day three lay the bottom course of blocks, day 4 pour in the floor?

Never done this before (obviously)

 

[John D v2.0]

The people down the road got a mini mix company to lay their greenhouse base, basically they mix and charge for what you need at the side of the road, then barrow as it's mixing.
With a normal ready mix they would have had to pay for pretty much a full load even if they only ordered 1m3, as the cost is in the delivery etc not so much in the material. So worked out cheaper for a small load.