Foundations and concrete mix

lynsiloo

Hi all. I am currently digging out my back garden for the foundations for a small extension. When pouring the concrete into the trenches is there anything I need to do if I can not complete it all in one day, or can I just keep adding to it when I get time? (Ready mix is out of the question due to access).
Second question: My engineer has specified class C35 concrete mix. Does anyone know the correct mix ratio as I will be mixing it myself.
Any info would be appreciated.

navig8r

How Small is small ?is it single or two stories?? how may cu mtrs of mix do you need ? This is the most important part of the building so you need to get it right and really ought to go down in one hit with a good consistancy of mix!! Edit: But to be honest I would be asking your engineer, then at least you would know you had the right answer!

Dave

lynsiloo

navig8r wrote:

How Small is small ?is it single or two stories?? how may cu mtrs of mix do you need ? This is the most important part of the building so you need to get it right and really ought to go down in one hit with a good consistancy of mix!!

Dave

It is a single storey, aprox. 3 meters x 4.7 meters. If I have calculated correctly it should be about 2.15 cu mtrs of mix. Within the founds will be a layer of a252 fabricated steel.

navig8r

What about minimix ?..if you have to barrow aggrigate to the site why not barrow the ready mix.

Dave

lynsiloo

What is minimix? It will be just myself doing the work so thats why I had not looked into ready mix.

navig8r

We have minimix in our area ,they are just small ready mix lorries, some bring it ready mixed and others bring the dry materials and some mix on site which I suggested because I thought you had restricted access ..look in your Yellow Pages for "concrete Ready mix"..You can also get the concrete pumped straight into the foundations in tube which can go right over the tops of a property but this is quite expensive..( look under concrete pumping)

Are you experienced at concrete mixing ie know the right order to put the stuff in the mixer for the most efficient through put and the drum does not clog up ?

can you rope some one in to go on the barrow for you or place an ad in the local paper shop or super market notice board for some help?

Dave

Humpty

3mtr x 4.7mtr x How Deep?

Humpty

a&akay

The ready mix companies usually have an allowed on-site time. We laid a large slab of your cubage between the two of us (wife and I) using 2 wheel barrows. The ready mix operator was quite happy to dole it out in wheel barrow dollop loads and it sure beats mixing it yourself (I have done both these ways lots of times).

leehal

I would stay away from mixing the concrete yourself, very labour intensive and also the fact that C35 has been specified implies that the compressive strength of the concrete is important. Even with ready mix companies it has been known for failures under testing, the chances of you getting the mix spot on when mixing by hand are slim.

I assume that you have imformed Building Control, they will need to carry out inspections when you have dug the foundation and also after you have poured the footing.

Minimix would be the way to go for me.

leehal

Just to add to that C20 is a standard footing mix, the ratios are 5 (20mm ballast):1 (cement)

Chances are your engineer is just covering his back and overspecifying.

lynsiloo

Thanks everyone. I have decided to go down the minimix route. They will mix it at the kerb side and wheel barrow it round to the back garden for me. Like other people have said, I will be getting the correct mix, will have to put in v. little labour myself and it should all be done within a hour. Thanks for everyones input, much appreciated.