# Mix ratio for gravel and cement



## flowerman (30 Sep 2014)

Whats the ratio of gravel (premixed sand and stone) to cement for making a good strong concrete mix for a wall foundation?

Is 4 gravel to 1 cement a good/stong concrete mix for 450mm deep x 450mm wide wall foundations? Or is it 5:1?
There will also be 8mm steel mesh in the foundation too (50mm up off the base).

Thanks.


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## Steven Barrett (30 Sep 2014)

I presume when you say gravel, you are using sand? I have used 4:1 or 3:1 in the past in mixing out loads for building a house. For the price of a couple of bags of cement, at least you know you have a good mix. 

I'm not DIY minded, I did what I was told!


Steven


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## flowerman (30 Sep 2014)

SBarrett said:


> *I presume when you say gravel, you are using sand? *I have used 4:1 or 3:1 in the past in mixing out loads for building a house. For the price of a couple of bags of cement, at least you know you have a good mix.
> 
> I'm not DIY minded, I did what I was told!
> 
> ...


 
Thanks for the reply.

Yes,bulk bags from of "batched gravel mix" (sand mixed with 5-20mm stone).
Mixed by Kilsaran for a well known a builders providers group.
I bought the gravel and steel mesh off the builders providers,and I got my bags of Irish Cement in BnQ for 4 euro 49 cents each.

Chap in the builders providers said 4:1 to me and you are saying 4:1 too,so I think I will got for that then.


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## flowerman (30 Sep 2014)

Just reading up on a few Irish and Uk building forums and websites.

Most of the builders and blocklayers say to use a mix of 1 cement to 5 batched gravel/ballast for foundations/footings.
Alot of them say that 1:4 mix is prone to shrinking and cracking so 1:5 is a good allround mix that is perfect for foundations for walls and garages.


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## Branz (1 Oct 2014)

the cracking and shrinking is due to the heat generated in the mix as it cures, [its an exothermic  chemical reaction,] especially if plasticisers are used which reduce the amount of water used.

If you keep the top surface wet, standing water wet, not just damp, for the first 7 days or so, then it will reduce the risks.


See here: 
http://www.cement.org/for-concrete-.../concrete-construction/curing-in-construction


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## flowerman (1 Oct 2014)

ircoha said:


> the cracking and shrinking is due to the heat generated in the mix as it cures, [its an exothermic chemical reaction,] especially if plasticisers are used which reduce the amount of water used.
> 
> If you keep the top surface wet, standing water wet, not just damp, for the first 7 days or so, then it will reduce the risks.
> 
> ...


 
Thanks for the advice,think I will play it safe  go with 1:5 mix.Theres steel mesh in the foundation aswell so I should be god.


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## Branz (1 Oct 2014)

flowerman said:


> Thanks for the advice,think I will play it safe  go with 1:5 mix.Theres steel mesh in the foundation aswell so I should be god.


No worries.
What I do is rent a small vibrator and it works wonders for getting it to flow if the consistency is right. A small amount of the proper admixture will really help.
http://www.sbsg.com/concrete/admixtures/
I mean proper, not Fairy liquid which is often used which destroys the concrete bond
If u space the levelling pegs close enough the vibrator will leave it level enough without any need for screeding or standing in the trench


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## flowerman (2 Oct 2014)

ircoha said:


> No worries.
> What I do is rent a small vibrator and it works wonders for getting it to flow if the consistency is right. A small amount of the proper admixture will really help.
> http://www.sbsg.com/concrete/admixtures/
> I mean proper, not Fairy liquid which is often used which destroys the concrete bond
> If u space the levelling pegs close enough the vibrator will leave it level enough without any need for screeding or standing in the trench


 
I didnt use any admixture.
I just mixed a ratio of 1 cement-5 gravel for around 4-5 minutes and then poured it into the footing.
A chap who I know well in the builders providers said to me this afternoon that I should have mixed 1:3 as this would give me a really good strong foundation.
He said Id get away with 1:5 but in future I should do 1:3 for any further foundation footings.

What do you rekon about this as Im confused as to what do in the future?

I still have 1 more footing to fill with concrete.


PS-I took your advice over the tamping.1st I used a piece of 2 x 2 wood to poke up and down quicklly to the base of the freshly poured concrete (did this with each wheelbarrow) and when the footing was full to the pegs then I gently tamped the surface with float trowel.The concrete more or less leveled itself when I did this and I got a nice smooth-ish surface just by tamping it.


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## Dermot (2 Oct 2014)

If the ground where you are pouring the concrete mix is good and your mix of 1 cement to 5 of your gravel mix is reasonably accurate you need have no worries.  In my experience 1 : 3 would be ridiculous.  Finish your footings tomorrow and sleep well.


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## flowerman (2 Oct 2014)

Dermot said:


> If the ground where you are pouring the concrete mix is good and your mix of 1 cement to 5 of your gravel mix is reasonably accurate you need have no worries. In my experience 1 : 3 would be ridiculous. Finish your footings tomorrow and sleep well.


 
Yeah the ground is good and firm at the base of the footings.
Thanks for the advice.

I measured the ratio with builders buckets for the gravel mix.
And then added half a bag of Irish Cement for every 5 buckets of gravel.I didnt over water either,I made each batch so that it wasnt too wet but wasnt too dry either.


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## flowerman (3 Oct 2014)

Boy oh boy what a day it is.Rain rain and more rain again.Spent late morning and early afternoon moving soil heaps around and leveling out part of the back garden with a mini digger,garden is now more or less a mudbath.Had to give in at around 2pm as it was very heavy rain that was falling.
Hope tomorrow is a better and drier day too.


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## flowerman (5 Oct 2014)

Need some help and advice here now.

The other foundation trench is flooded with rain water,a good 18 inches depth of water has filled the trench.

How best to deal with this problem?
Do I need to drain every last drop of water out of the trench and do I now need to put in a few inches of 804 hardcore?

Friend of mine says to dig a deep hole at one end of the trench and this will be a sump where I can drop in a pump and suck all the water out.

Can I still pour concrete into the foundation if there is rainwater flowing into it from the surrouding garden?

Will water in the foundation trench weaken the fresh poured concrete mix?

Thanks.


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## flowerman (13 Oct 2014)

I did some more concrete work today.
Laid some steel mesh 50mm up off the bottom of the foundation and then did a mix of 4 batched gravel to 1 cement.
Had to drain out alot of standing water over the last 2 days due to the ground being saturated,I scraped out the layer of mud and silt and then put down a layer of hardcore and whacked it down to give a firm base.There was still some ground water seeping up through the hardcore as I was pouring the concrete but I got out as much water as I could before placing the concrete.


Thanks to those kind people above for posting the good sound advice.


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## flowerman (12 Nov 2014)

An old boundary wall foundation had to be underpinned last week.This is how the wall foundation was underpinned (offset underpinning),done in 1 meter stages like this with 8mm steel mesh and 12mm rebar to add support and strength.Then it was all back filled and covered over with 6 inches of soil.
https://www.flickr.com/photos/127582733@N07/15587910100/
https://www.flickr.com/photos/127582733@N07/15587910220/


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