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Posted: Mon May 12, 2008 10:38 pm
by Probs
Hi folks,
As I'm sure many of you do this for a living or indeed more frequently than me maybe you can help me out 
I'm looking for an easy way to calculate how much cemement/all-in-ballast I would need for foundations of a given size.
Does anyone have a formula that they use for this ?
I'm looking to use cement and ballast at a ratio of 1:6.
Thanks chaps,
- Jamie
Posted: Mon May 12, 2008 11:54 pm
by lutonlagerlout
for 1 bulk bag of ballast you will need 5 bags of cement
i.e. 850 kg ballast : 125kg cement i know this doesnt sound quite right but believe me it works ,the cement and ballast have different densities etc
cheers LLL
Posted: Tue May 13, 2008 7:57 am
by Probs
Thanks Luton but I think you might have miss-understood my question
I know how to work out the ratios but I'm struggling to work out for instance how much I would need for say a footing which is 3m long 1 foot wide and 1 foot deep. I.e. would 1 25kg cement bag + 6 25k ballast bags do the job ?
Is there any easy way of working this out ?
Thanks again,
- Jamie
Posted: Tue May 13, 2008 11:49 am
by matt h
area in cubic metres = apprx 0.3
go to main site and use tables already setout for you to calculate your particular mix.. easy if you can read:p
Posted: Tue May 13, 2008 9:44 pm
by Mikey_C
having worked out your cubic meters required (LxWxH, all in meters), you then need
your looking for the C20 concrete calculator
if using ballast, add grit sand and gravel weights together.
Posted: Tue May 13, 2008 11:04 pm
by lutonlagerlout
i would go 3 m by .4m by .4 m a wall shoulkd have a foudation at least 10mm wider than the wall so if its a 225 wall then the foundation should be 425 wide
for this 1 bulk bag of ballast and 5 bags of opc will suffice
rgr that?
LLL :;):
Posted: Wed May 14, 2008 9:27 am
by Rich H
Should be bang on. 0.4 x 0.4 x 3.0 = 1.05t ~ 0.85 + (0.25 x 5) = 0.975t
Posted: Wed May 14, 2008 4:05 pm
by Bob_A
Mikey_C wrote:if using ballast, add grit sand and gravel weights together.
That sounds logical yet many online calculators say that when you use all in ballast the weight required is actually less than the weight of adding sand/aggregate together.
There are a number of sites with calculators that do that, here's a few
http://www.diyhelp.org.uk/estimatorsPages/concreteBallast.php
http://www.diyhelp.org.uk/estimatorsPages/concreteNonBallast.php
http://www.source4me.co.uk/calculate_concrete_mix.htm
http://www.workswright.co.uk/maths/maths.shtml
Why do they suggest that you need a bit less when using ballast?
Posted: Wed May 14, 2008 10:01 pm
by Mikey_C
in the words of the dragons den, just to let you know where I am "I'm out", apart form the fact that "all in ballast" as discussed on this site can be an uncontrolled "doesn't conform to any particular specification", I couldn't offer any suggestion why less ballast is required. Hopefully one of the pros on here can.
However, are you worried about under ordering on quantities or are trying to get a perfect mix?
If it is the later you should be looking at computer controlled on site mixing trucks or ready mix, not throwing ballast and cement at a mixer with the usual inherent errors.
If it is the former I am guessing you putting something on this footing and will require cement for this and ballast is always handy on a working site.
Posted: Wed May 14, 2008 11:06 pm
by lutonlagerlout
a normal builder's mixer holds about 1 big barrowfull of concrete
you get 10 of these out of a bulk bag ,so you use 12.5 kg (half a bag) of cement, roughly 8-10 pints of water (half a bucket) and about 12-14 shovels of ballast (depending on shovel size)
abracadabra foundation mix concrete!!!
LLL
Posted: Wed May 14, 2008 11:35 pm
by Bob_A
Mikey_C wrote:If it is the former I am guessing you putting something on this footing and will require cement for this and ballast is always handy on a working site.
It is the former, the mix doesn't have to be accurate and like you say it's always best to over order. ballast doesn't go off so it will get used eventually.
I'd like to find the answer to this one, not because it's important but because it's bugging me.
Posted: Thu May 15, 2008 7:12 pm
by Mikey_C
ahh! the thirst for knowledge. more than acceptable, let us know when you find the answer.
Posted: Sun May 18, 2008 10:44 am
by Probs
Hi folks,
JUst managed to get some time to check the site, Firstly I'd like to say thanks for all the replies the link to the calculator on http://www.source4me.co.uk/calculate_concrete_mix.htm has been extremely useful. At least to confirm what sort of quantitys I should be looking for.
Secondly it gives me an idea of how much cash I should be looking to spend and of course how much humping and dumping I'm going to be doing 
Since I'm looking for a relativly small amout of concrete (Just under 1.5 m sq) would it be cheap to have that amount ready mixed and pumped to where I want it ?
Or would it be considerably cheaper to buy and mix it myself ?
Thanks again folks, I hope your associated weekends are going better than mine !
- Jamie
Posted: Sun May 18, 2008 12:04 pm
by matt h
small amount do it yrself. Isnt it 1.5 cubic metres?:)
Posted: Sun May 18, 2008 12:38 pm
by Probs
Yeah sorry. Typo !
Problem with mixing it myself is getting it to the location. It's a midterrace house so a lot of barrowing to do, I'm just worried it'll start drying out and stuff ...