lean mix concrete ratio

firbyfred

I am building an extention which I have build up to dpc level, on the plan the cavity below dpc is filled with a lean mix concrete, what ratio sand/gravel to cement should I use?
thanks

wallbash

Lean concrete is 'cheap' concrete
i.e more stones .... used to fill spaces
If you haven't enough smash up a few bricks.

So about 6 /3/ 1 six stone/gravel to 3 sand and one cement

firbyfred

wallbash wrote: »

Lean concrete is 'cheap' concrete
i.e more stones .... used to fill spaces
If you haven't enough smash up a few bricks.

So about 6 /3/ 1 six stone/gravel to 3 sand and one cement

Thanks
It is a big extention and it is going to take about 1.5 cubic metres of concrete to fill the cavities, is there a way to work out how much sand and gravel?

wallbash

Google is your way

try http://www.benchmarkbuildingsupplies.co.uk/calculator.htm

wallbash

Just worked it out using the above link .... tells you even how much water to add :j

Wonder if it supplies the tea!

wallbash

It is a big extention and it is going to take about 1.5 cubic metres of concrete

Thinking are you sure thats enough

Various calculators are on the web to make the maths easy

Tucker

1.5 cubic metres to fill the cavity? It's not big.........it's massive!

Assuming you have a 100mm cavity, how long is the outer parameter?

Remember you would normally only fill the cavity to 225mm below DPC and not all the way to the top of it.

wallbash

Assuming you have a 100mm cavity,

This is the bit I getting confused on

Do you think firbyfred is really talking of the whole floor ??
Therefore 1.5 might not be enough??

firbyfred

Tucker wrote: »

1.5 cubic metres to fill the cavity? It's not big.........it's massive!

Assuming you have a 100mm cavity, how long is the outer parameter?

Remember you would normally only fill the cavity to 225mm below DPC and not all the way to the top of it.

Its about 7+ metres square , the cavity is 150mm for stonework, and I have allowed for the 225mm below dpc.

Tucker

7 metres square is only 3.5m by 2m in dimensions?

Are you talking 7m by 7m? 49sqm total?

If so, you are filling a 150mm cavity at 500mm deep for that amount of concrete.
Is that about right?

1 cu metre is about 16 wheel barrows full, so you will want 24 wheel barrows worth of gear.

vaio

[FONT=&quot]Does sound like an unfeasibly large amount of concrete for a cavity fill[/FONT]