Readymix or self mix?

[jat147]

Afternoon,
We're putting up a retaining wall in the garden, footing are dug and I'm getting confused about volumes?

Area of the trench to fill is 1.8 m cu

Quotes for readymix are between £238 - £275

Sounds expensive, I can borrow a mixer but cant figure out exactly how much aggregate is needed to make 1.8m?
The figure 1.75 t per m3 of aggregate seems about right - is that 3.5 tonne bags plus cement?
Thanks in advance.

 

[ChapiTheBricky]

You're about right there.There is an exact science to this but it's exactly that, science and I'm a bricky. Your exact volume has so many variables it's hard to nail perfectly, amount of water used, how well the concrete is vibrated etc.

 

[^woody^]

In practical terms, you would order two bulk bags of sand/gravel, 10 bags of cement and just use that.

 

[jat147]

Thanks chaps, muchos gracias

 

[noseall]

In practical terms, you would order two bulk bags of sand/gravel, 10 bags of cement and just use that.

Er....not quite Woodster.

A 1 tonne bag of sand & gravel (plus cement obviously - 6 bags) will only do aboot half a cube.

 

[noseall]

how much aggregate is needed to make 1.8m?

About 3 - 3.5 tonne plus 20 bags of dust.

This will set you back about £200.

 

[themiddleagedun]

Calc. batteries gone I'd say 4 ton of ballast & 25 bag of cement.
Or, best way, ready-mix

 

[^woody^]

Funnily enough I've done a few of these now, and have been a tonne short on the other jobs too

I've assumed that the OP has not cut the trench out perfectly square with a razor blade, and that his cubed dimensions are to the top of the trench (ie LxDxH) which in reality is too much as the strip needs to be lower.

He can always lay an extra course if the concrete is short

 

[theoldun]

woody, we always respect honesty

Nose is about right, although we would budget for 22 bags dust. Nothing worse than being bag or two short at the death. You can use them up in your wall.

If you are buying so called tonne bags ballast, remember they usually only hold 850kg all as BMF regulations. The tonne is for lifting and carriage purposes.

To make life easy run materials round dry and batch up alongside foundation.
oldun

 

[noseall]

It takes 2.2 tonnes of material to produce 1m³ of concrete.

1750kg's of ballast.

300kg's of cement.

Plus water.

Many people are fooled into believing that a 1 tonne bag of ballast will produce a cube of conc. Wrong.

Readymix concrete is by far the most efficient way of producing concrete although not always logistically practical. However miximate type service is more expensive per cube but is countered by its practical value.

 

[wavetrain]

Why not collect 0.9m3 of used bricks from skips in your area to add to the trench in layers alternating with the concrete to save some money and effort of mixing but at the cost of time in collecting the bricks?

 

[jat147]

Thanks Wavetrain, I've got quite a bit of hardcore already.

I thought I read on here somewhere about not putting hardcore in the footings? Does it affect the strength at all??
I can see the point though

 

[noseall]

Why not collect 0.9m3 of used bricks from skips in your area to add to the trench in layers alternating with the concrete to save some money and effort of mixing but at the cost of time in collecting the bricks?

Gotta be a wind up!

 

[wavetrain]

jat147, I have re-read your post and now see it is for a retaining wall and not a simple wall so you may need sideways strength in the footings I guess, so sorry for the duff info, however as I detail below, I feel my composite footing would be stronger than the wall above it, so may be strong enough for your application.

It is not a wind up nosy! I have more than that volume of used bricks ready for this application in footings that are going at the edges underneath a reinforced concrete slab. Their purpose being to stop the slab tilting over time. By having the bricks ready in small piles along the trench and carefully placing/laying with wide gaps that are filled with the next pour of the wet stuff', you are building a 'wall footing' underground with wide joints where the concrete is used as the morta, and so the DIYer has the bricks to hand and only needs to mix and barrow half the concrete. The used bricks can have cement morta firmly stuck to them, but must be free of lime based mortas.

People actually advertise used bricks suitable for hardcore on flebay, mind you they don't get many takers as they are always around in the suburban skips.

I saw a local news feature on TV a few years ago about 'skip addicts' - people who cannot resist looking in skips and taking items away for use/projects etc, has anyone known someone like this?

In fact I have picked a good few items up at my local dump (with their permission of course). On occasions I have come back with more stuff than I took to dump in the first place.