Confused About Material Quantities for Concrete

[EasyGoingPat]

Hi,

I am laying a large area of concrete on sandy soil. It will not be required to hold the weight of a car, but I do want it to last. I've read lots of information on laying concrete (including info on this site), but I remain confused about the quantities of materials I need.

I went on one website which attempted to clarify the issue. It specified how many bags of cement, how much 'coarse aggregate', how much 'sharp sand', and how much 'ballast' was needed for a cubic metre of concrete. Thing is, if you read the definition of 'ballast', it says it is a mixture of aggregate and sand. So do I need them all, or is ballast an alternative to separate sand and aggregate? Adding up all the materials they listed would have had to reduce in volume by about a factor of four for me to end up with one cubic metre of mixed concrete. Surely that can't be right?

I have erected a wooden frame, and I have roughly 75mm of compacted hardcore already laid. This leaves roughly 100mm still to fill. I have calculated the volume of this at about 4 cubic metres. What do I need to fill this? I'd be extremely grateful if someone could give me a straight, easy-to-understand answer.

Kind wishes ~ Patrick

 

[Jackrae]

4 cube is around 10 tonnes. Are you prepared to shovel all that ?
Why not simply order a bulk delivery of ready-mixed concrete.

 

[EasyGoingPat]

Hi,

I did want to do that, but unfortunately there is no access for anything larger than a wheelbarrow.

I have partitioned off the space, so that I can do it in manageable blocks, and I have probably overestimated at 4 cubic metres; it's probably more like 3. Still a lot of hard work though.

But the job ain't going anywhere until I work out what I need to buy to mix it up. I can't believe the difficulty I have had trying to work out such a commonly-used piece of information.


Kind wishes ~ Patrick

 

[wrathkeg]

ballast is sand and gravel already mixed. so some sites might talk about a mix of 4:2:1 (or other stronger or weaker mixes). That means 4 parts gravel to 2 parts sand to 1 part cement. Alternatively, add the first two numbers together to get the amount of ballast: so 6 parts ballast to 1 part cement.

the best site I know of on this sort of thing is http://www.pavingexpert.com/ which includes loads of guidance on concrete, and has reliable calculators. the bottom part of this page will probably be especially useful

http://www.pavingexpert.com/mortars.htm

and the advantage of using one site is it avoids the sort of confusion you've been suffering by looking at loads of different ones

 

[wrathkeg]

Thinking about this more, I wonder whether you have considered slabs as for a patio? You could lay these on a dry mix of sand and cement (10 parts sand to 1 part cement, 50 mm thick) with heavy duty 50 mm slabs on top. That should last, and would get you to the height you are after. Lay the slabs round the edge on a wet mortar mix. The paving expert website has loads of advice on this.

This way while you would have to pay for and carry the slabs (obviously) there would be a lot less dry material, shovelling and mixing. I also find it's easier to work at my own pace with slabs than with concrete, which might help given the size of area you are looking at (about 6mx7m?).

 

[EasyGoingPat]

Hi,

I did consider slabs, but some parts of the area are a complex shape, so I figured that I'd have a problem cutting the slabs. Maybe I could get a cheap load of broken slabs and do a crazy paving thing.

Thanks for the suggestion though.


- Patrick

 

[wrathkeg]

angle grinder? depending on what's at the edge, maybe you could make your paving a regular shape and have gravel in the gap between slabs and the irregular edge.

 

[r896neo]

honestly get readymix. The cost of the materials for you to mix it yourself will almost be as expensive as ready mix.

If you have 2 men and your not going more than 30m you could barrow 3 cube in half an hour or maybe 40 mins at the most.

 

[EasyGoingPat]

Thanks for the suggestion.

I will look around for local companies who do ready-mix. So the delivery truck will be okay about waiting around 40 minutes while we move 3 cubic metres? There is nowhere for them to dump it and leave us to it. We're on double-yellows, too, so some drivers are funny about stopping.

Regarding the other suggestion to cut slabs, I do have an angle grinder, but my experience of cutting with it is that it takes ages. Admittedly, I don't have one of the fancy diamond discs, which I'd definitely buy if I were going down this route. How good are these disks? Do they make concrete cutting easier?

- Patrick

 

[wrathkeg]

Should be fine though you could always check first. Certainly I have worked on projects with friends where the drivers waited about that length of time while we ferried concrete up gardens etc. And they poured the concrete straight into the barrows. Dunno about the yellow lines - nobody round here seems to care about that kind of thing

 

[r896neo]

You are allotted a waiting time of between 20 mins and half and hour depending on the company and sometimes will have to pay for extra time but its only going to be a 15 quid or similar.

You may be best getting volumetric mix a mate type service as it may work out cheaper. If you get 3 cube delivered on a 5 cube lorry you have to pay for the empty space. It sounds mental but thats how it works.

 

[EasyGoingPat]

...what you mean my the type of mix you mention.

 

[r896neo]

You can get concrete delivered on a specialist truck that mixes exactly how much you need rather than a large truck which may hold 7 cubic metres having to come with your 3 cubic metres and then you pay maybe half rate for the empty space in it. These large ones are usually readymix where its mixed elsewhere

These mix what you need type are called volumetric. Mix a mate is a company doing this type of delivery.

Google them and get a quote from a few different suppliers of both volumetric and normal readymix suppliers.