mixing concrete

[nottsrob184]

Hi
I am building a rear extension and have dug the footings which are a total of 46 feet x 2ft and the concrete needs to be 18 inches deep (existing footing depth).
Access to the rear of the property is tight and i will need to chute any ready mix over 25 ft.
I have had a quote or two...around £450 for 4.5Cubic mtrs....but to get this pumped will be over a grand!!!.
I am in two minds to buy or rent a mixer and do it on site with a mate.
Questions are....do you think its do-able and does the footings have to be layed in one go or can i do it over a weekend if it gets too much.
How many bags of cement do i need and what strength do i mix the ballast, sand and cement....sorry for so many asks but i am a bit green on this.
Thanks

 

[hotrod]

Access to the rear of the property is tight and i will need to chute any ready mix over 25 ft.
I have had a quote or two...around £450 for 4.5Cubic mtrs....but to get this pumped will be over a grand!!!.
I am in two minds to buy or rent a mixer and do it on site with a mate.

Don't mix it yourself - not 4.5 cube. £450 for 4.5m³ sounds about right, maybe slightly on the high side phone around you may get it down to £90/m³.

When you say access is tight and you need to chute any ready mix over 25ft, are you saying you can get the wagon to discharge 25ft from the trench? If so get a couple of mates with barrows - 25ft is nothing. You'll have it done in no time.

 

[RonnyRaygun]

Don't mix it yourself - not 4.5 cube.

Agreed. 90 litres per mix will take 50 mixes...that's a lot of work!

And it won't work out any cheaper. 4.5m3 of concrete weighs in at 10.8 tonnes, so you'll need just under 10 tonnes of ballast and well over a tonne of cement. That's going to cost you more than £450 before you've hired the mixer.

Also, getting the mix delivered you'll get the correct C20 mix - bet DIY concrete doesn't often get mixed that accurately - and some suppliers will mix at site and only charge for what you use, so no wastage either.

50 or 60 barrowloads between three or four people will be done in half an hour.

 

[RedHerring2]

I think I've mentioned before that, from experience on a few occasions, 1 cubic meter, mixed by hand (in a mixer) and laid is a long day's work for two average DIYers.
The speed of the mixing in the mixer is the critical issue.
You can barrow it & level it as quick as you can mix it.

 

[RonnyRaygun]

the concrete needs to be 18 inches deep (existing footing depth).

Nottsrob, I'm sure I'm asking a stupid question but how far down have you dug? More than 18 inches right?
You need to be at least a metre below ground level to prevent frost heave; some older houses (such as mine) have 12 inches of concrete 400mm below ground level. The existing foundations might not be satisfactory for the current building regs.

The building inspector will have to agree the footing depth before you pour the concrete anyway, has he done this?

 

[nottsrob184]

the concrete needs to be 18 inches deep (existing footing depth).

Nottsrob, I'm sure I'm asking a stupid question but how far down have you dug? More than 18 inches right?
You need to be at least a metre below ground level to prevent frost heave; some older houses (such as mine) have 12 inches of concrete 400mm below ground level. The existing foundations might not be satisfactory for the current building regs.

The building inspector will have to agree the footing depth before you pour the concrete anyway, has he done this?

Yes BI has been and Ok'ed it.
My trench is 1M deep at least and the existing house footings are only about 700mm down....i have dug below the existing house footings so will be lower than them and my footing will be 150mm thicker than existing.

 

[jeds]

Hand mixing is out of the question for that quantity. I'd question the pump price. Find somebody with a moli pump. They are smaller than boom pumps and cost a lot less. Ideal for small jobs.

 

[noseall]

We will hand mix 6 tonne (about 3 cube) and have it laid in 5 or 6 hours.

However you are best hiring a small in-line pump and sorting it that way.

There are instances where the pump arrives and not the concrete so some will charge sitting time, this is particularly relevant when having more than one truckload.

There is a a period of set-up and clean down time also plus travelling to your site which does eat into the day somewhat so the differences in time taken are often marginal.

As for effort, there is nowt easier than a pumped readymix load.

Incidentally the last pump cost us £168 and that was pumping 10 cube.

 

[theoldun]

Let me tell you how we look at concrete.
You have 14x.600x.450 so you only need 3.8MC and not 4.5MC .
For 3.8 MC working on a 1-6 mix all in, you will need 8 tonne ballast loose and 48 number 25kg dust. If you farm around you should be able to buy that for £367.00 vat inclusive. Hire of 4/3 mixer weekend say £26.00 vat inc, plus possible del and col charge.
For that small quantity we would batch on site. Set your mixer and water butt up by side of trench, run materials in dry so that you are not humping in nearly 2 tonne water. Throw it through a 4/3 mixer only using 12 shovels of ballast and half bag cement. Keep it wet, turn it over and drop in trench. Two good lads should throw 50 to 60 gauges through in one hour and be washing up by mid day.
You can push the mix out on founds to 1/3/6 but we stick to 1/2/4/ as we run it round a bit wet in founds. Why we like batching small quantities like this is, you are not governed by weather, not hanging around waiting for concrete to turn up, not having to find some where for lorry to wash up and with drum lorry you are only allowed 5 mins per CM to of load and then you are on £60.00 hour waiting time and for 3.8MC you still have 83 full dead weight barrows to push in and tip up.
The chances are you are two or three barrows short or over the top. If you are over the top, and they take it away, you then have a charge for this plus a washing up charge back at depot.
If you want to use ready mix. Go for a Volumetric supplier not a drum mixer supplier Mixomate carry 3 barrows on board for their customers to use free of charge plus they have a waiting time of 20minutes per metre. They also have a third of metre dumper on board which will pass through a 800mm wide opening. The lorry driver drives this, but you have to pay for the service.
Some 8 legger volumetric lorries backed straight on have a discharge chute 6.500 long which would reach into your trench. However mixomate only have a 3.700 chute but you could cobble up an extension with three scaffold boards and polythene.
With volumetric, you can have delivered what quantity you want and what mix you want. Tell the driver you want a trench flow and he will design mix accordingly. Trench flow or self levelling as some call it runs out like water and will flow all round trench. Budget for say £120.00 metre cube.
One other thing, the jumbo bags, bulk bags normally referred to as tonne bags only hold 850kg. The tonne is only for lifting and carriage purposes..Hope this helps. Guidance only. old un.

 

[theoldun]

Noseall has got it right. The easy way is a pumped ready mix pour, but circumstances and budget do not always allow. old un.

 

[Thermo]

we would use mixamate for that. excat quantities and as old un says the power barrow is superb. its quick, its easy and they wont be on your back as much as the readymix guys for time. They also clear up all their mess and hose down the road etc. Cant beat them.

 

[nottsrob184]

we would use mixamate
Whats the difference betweem miximate and maximate?....sorry for being a dumbo....is it a company of a method?.

At the moment i am in 2 minds weather to hire or buy a mixer and mix myself with 2 mates or get delivered and buy 2 more barrows and get them to help me barrow it in.
Also.."oldun" is right...it is 3.8CM...i just thought i would need a bit extra for safety.

Thanks to everyone for your replys...keep 'em coming

 

[Thermo]

http://www.mixamate.co.uk/

 

[hotrod]

I was the first to reply on this post and I'm the only one not to have been "thanked"

'Always a bridesmaid never the bride'

Also.."oldun" is right...it is 3.8CM...i just thought i would need a bit extra for safety.

I would be adding 10% to your 3.8 for wastage - that's pretty standard to cover yourself in a case like this. You can 'lose' the extra and not be left with a load of concrete to get rid of.

 

[noseall]

You will bang your head against a wall trying to decide what to do as it is a swings and roundabouts situation.

I have been both lucky and unlucky with readymix and pumps.

The one thing i can say is you are the master of your own destiny if you mix your own.