# Foundations

Discussion in 'Getting Started FAQ' started by Gerry46GB, Jul 30, 2018.

1. ### Gerry46GBNew Member

Hi

Can any help me . I want to put a trench in and fill it with concrete/cement but unsure how much .
Measurement are as follows. Length roughly 9 m by 30/40 cm wide by 30/40 cm deep.
Have used a ready mix mix site for concrete and they only do 1 cubic metres.
I want o know how many bags of concrete and sand would I need and also what would be better Ballast or sand.
Hope some one can help me.

2. ### IsitreallyWell-Known Member

L x w x d =

× 2.2 gives total tonnage, divide by mix ratio, in this case 5.1 to get amount of ballast to amount of cement, with cement divide by 25 to get amount of bags.

So in your case assuming the W and D are 350 average of your measurements.

9 x .35 x .35 = 1.1025 x 2.2 = 2.5255 tonnes ÷ 5 = .4851 cement.

Or 20 bags cement and 2 jumbo bags of ballast. Should be about right.

KIAB likes this.

4. ### Gerry46GBNew Member

Hi Isitreal
First of all thanks for your reply.
When you say 20 bags of cement are you talking about 25 kg bags, also when you say ballast would it be correct in saying that aggregate is basically the same and does the same.
I want to dig a trench with the measurement of L 9 m x W 30 cm x D 30 cm and I get 8.1 so under 1 m3 .
Now I know this will sound daft but if I was mixing by hand and I know it will take some time But I if was t use a 3 litre empty bucket would it 1 cement 3 ballast and water.

5. ### DIY wombleActive Member

What's going on top , might need to consider steel or fibres

6. ### IsitreallyWell-Known Member

With the dimension you propose you would need.

14 bags of cement.

Still need 2 jumbo bags of ballast but will have some left over (still cheaper than buying small bags)

The mix ratio I've worked on is 5.1 because the trench is quite shallow so went stronger.

Buy yourself 2, 2 gallon buckets (a couple of quid ea) one as a gauge bucket and one for water.

Also consider hiring an electric mixer for a day, not only will
this make mixing easier, it will also produce a better mix.

7. ### KIABWell-Known Member

Hire a decent petrol mixer, cope with a larger load.

https://www.hirestation.co.uk/tool-hire/Concrete/Cement-Mixer-Hire/070015/

8. ### Gerry46GBNew Member

Hi.
Sorry to bother you again. When you say 5/1 ratio. Are you talking about 5 ballast to one cement.
Thanks

Yes.

10. ### DIY wombleActive Member

Steel or fibres , assume not necessary , 9m long , what's on top ,

11. ### KIABWell-Known Member

Don't think it's needed.

But, I h ave occasionally used adfil polypropylene fibre in foundations, but usually use them for screeds,floors, & even with filler when filling deep/large holes.

12. ### Gerry46GBNew Member

I have large boulders want to reuse for a small retaining wall as my garden goes on a small slope.

13. ### DIY wombleActive Member

Did a 1-2' rendered retaining wall on shallow footings as didn't want to cut neighboring trees , 2 years later the biggest tree blew over in a storm ,the 5 m wall stayed in one piece with no cracking at all , although lifted 3" lucky I had plenty of steel , just thought I'd ask cheers , I like arty stuff show us some pictures when your done

14. ### Gerry46GBNew Member

Hi. As you may have guessed by now not a builder.
When you say 2,2 gallon buckets use one for a gauge bucket and one for water.
I know this a stupid question but when you say use one as a gauge bucket do you mean. Use this one for ballast or cement fill and use the ratio of 5 buckets to one bucket of cement and mix and add the the 2 gallon bucket of water.
If using a mixer out in double the amount. .
I know pain in the ****.
Never done it before and got quoted 900 for a trench and foundation.
If I can do it myself saving 600 almost. . Thanks again for your reply.

15. ### IsitreallyWell-Known Member

Yes 5 buckets of ballast to one cement.

The other to add water as required.

The reason for 2 buckets is a wet bucket make it fum when adding cement.

16. ### Gerry46GBNew Member

HI
Once I have the trench done and I want to reuse the boulders I have to build a small retaining wall can you tell me a good mortar mix for them.The boulders are roughly 30 cm in height and 20 cm wide and about 25 cm long.
As there are large and heavy,
I can send you pictures of them if that helps to give me a rough idea.
Gerry.

17. ### blannderNew Member

It's better to have extra bags from your estimation.