Concrete Mix Help Please

[rdwessex]

Hi. I am building a small double brick retaining wall, about 550 mm high.
For the footing, I have been told a concrete mix of 4:2:1 (aggregate, sand, cement) would suffice. I am looking at buying in bulk bags of ballast (mix of 20 mm shingle and sand). But, I don't know how much ballast to mix with cement to attain the same mix (as I don'r know the ratio of the ballast mix)...?
Thoughts please?

 

[Charlie George]

6 ballast to 1 cement will be ok, how much have you got to mix as readymix can work out similar price but a lot easier than mixing your own.

 

[rdwessex]

Thanks. Quite a lot. The concrete is primarily for the wall, but I will use the same mix as a base of a patio too.

 

[George_engineer]

If it's more than about 1.5 cube, get a volumetric mixer booked.

 

[Ivor Windybottom]

If you want equivalent to 4 aggregate, 2 sand then you need 5 ballast, not 6.

Ballast is denser than gravel, as the sand is between the bits of gravel. Some of every scoop of gravel is fresh air, which the sand will later fit into.

 

[stuart45]

The standard mix for a strip foundation used to be 1\3\6, which dependant on the gravel size was closer to 6/1, because as Ivor said the sand fills the gaps between the gravel gaps.

 

[noseall]

If you want equivalent to 4 aggregate, 2 sand then you need 5 ballast, not 6.

Ballast is denser than gravel, as the sand is between the bits of gravel. Some of every scoop of gravel is fresh air, which the sand will later fit into.

6:1 (ballast/dust) is a standard concrete mix.

 

[Ivor Windybottom]

It's probably more like 1:2.5:5 though, i.e. weaker.

 

[George_engineer]

Depends what the application is.

You could get 1:8 to provide a solid mass of concrete. For a wearing surface or exposed to weather it'd need to be 1:5.

For a smaller mass concrete footing - if it's just mass pour 1:6 is fine. If you're adding reinforcement bump it up to 1:5.

 

[rdwessex]

Well, thanks all. Not sure I'm much clearer as everyone is giving different answers.
On another point, how dry does the ground need to be for pouring concrete? As all of us in the UK know, the weather has been tonk lately. Can concrete be poured on damp ground where my wall footing is going?

 

[Charlie George]

Damp ground will be fine (how would we build anything in this country if it wasn't) and 6:1 for a footing is correct

 

[Mottie]

When I had my footings poured, it was raining so hard, I had to hire a submersible pump on the day of the pour to empty the trench. As soon as it was empty, the concrete was poured.

 

[noseall]

On another point, how dry does the ground need to be for pouring concrete? As all of us in the UK know, the weather has been tonk lately. Can concrete be poured on damp ground where my wall footing is going?

Concrete or cement LOVES water. For the sake of the foundations though, it's preferable to scrape any slush mud from the trench bottom.

 

[noseall]

Well, thanks all. Not sure I'm much clearer as everyone is giving different answers.

Its six parts ballast to one cement. Ignore any posters that try and tell you any different. You can make it a wee bit stronger if you wish, however its more about thoroughly mixing the gear.