# Forum Home Renovation Concreting  concret mpa rating

## sama

HI all 
        i am doing a deck extension,and have dug to footing holes 400x400x600mm,as per enginners drawings,and was wondering if anyone could give me the "recipe" for 40mpa rated concrete...ie what ratio of sand/cement/aggregate i need to mix to achieve a 40mpa rating for my concrete.

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## skot

3 gravel
2 sand
1 cement 
If you buy cement blend from a landscape supplier it will have the correct gravel/sand ratio so it would be 5 sand/gravel blend to 1 cement. 
The secret is a dry mix...the more water you add the weaker the concrete. 
The mixed concrete should be evenly mixed but not runny (water wise)

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## sama

40kg of mix to 20 litres of water,does this sound about right for 40mpa?

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## Bloss

> 40kg of mix to 20 litres of water,does this sound about right for 40mpa?

  Amount of water will be variable according to the mix - you start with less than you think it might need and add slowly. What you don't do is throw in all the water on an expected ratio - recipe for too wet (and weak) concrete!   :2thumbsup:

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## intertd6

ratios for 40mpa mix, 20mm agg = 1 cement : 1.5 sand : 2 aggregate
water ratio (kgs) is 0.5 water to 1 of cement
regards inter

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## Terrian

:confused: 
1) Why would you need 40mpa concrete for footings for a deck, beyond me, 25mpa would be more than fine. 
2) 40kg conmix (the bags with screening, sand & cement, ready to add water) are approx 20mpa, the quickset version is about 15mpa 
3) 3 gravel 2 sand 1 cement is *not* 40mpa mix 
4) 2 gravel 1.5 sand 1 cement is much closer to 40mpa (I have not looked up the specs, but it does sound about right) 
Add your water a bit at a time, all the ingredients need to be mixed evenly, if too much water the stone sinks to the bottom, the sand on top of that and the cement floats to the top) 
Too much water and leads to too much shrinkage and weakens the mix

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## sama

thanx all...got a truck in in the end :Sneaktongue:

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## Bleedin Thumb

> :confused: 
> 1) Why would you need 40mpa concrete for footings for a deck, beyond me, 25mpa would be more than fine.

  
,,,,,,,engineers specifications......say no more :Roll Eyes (Sarcastic):

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## Terrian

> ,,,,,,,engineers specifications......say no more

  bloody ridiculous, just some engineer going way over board to cover his/her rear end *, to hell with the unnecessary excessive expense.    

> thanx all...got a truck in in the end

  awww, you wimped out  :Biggrin:  
* the 4 letter word starting with A, ending with E and having R & S between is censored  :Smilie:

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