Concrete Mix Ratio ?

[Mystic Wind]

Hi,

I am in the process of building an extension to a single story double garage which is actually situated in my back garden.

Although the original standing building doesn't look to be built on more than an approx 150mm deep concrete base, I have dug footings that are approx 300mm wide & 600mm deep.
All of the concrete/mix information I can find however seems to be a little confusing, if not somewhat contradicting .... or perhaps it's just me.

Pouring is probably the last part of this project that I am going to be able to do by myself but I don't really want to make an ass of it.

Any suggestions on what cement:sand:aggregate:water (or whatever) mix I should be using would be greatly apprieciated.

Kind Regards,

 

[TexMex]

Hello Mystic Wind and welcome.

Any suggestions on what cement:sand:aggregate:water (or whatever) mix I should be using would be greatly apprieciated.

You should use a 6:1 mix (6 parts 20mm aggregate to 1 part Ordinary Portland cement). The word "aggregate" actually means that it includes all sizes upto and including. Therefore no need to add sand separately, it's already in there.

 

[Mystic Wind]

Cool ... I thought 5:1 so wasn't far out I guess.

I've learnt so much today what with finding this site.

Thanks for your help.

 

[countygardens]

I've learnt so much today what with finding this site.

I'm suprised you learnt anything with sme of the argumentative posts on threads such as render

 

[TexMex]

I'm suprised you learnt anything with sme of the argumentative posts on threads such as render

Oh, did I forget to suggest the PVA as an additive to make the concrete more waterproof

No, don't do it, it's really not a good idea.

 

[countygardens]

lol

 

[Mystic Wind]

Hello again,

I really want to get this done before we reach sub zero temps, but trying to dodge the rain is proving difficult .

I have a couple more questions (if you'd be so kind):

Can I pour in the rain or is this not advisable ?

Also, is it also possible/okay to pour in sections?
What I mean by that is that I have approx 7m dug at the moment ... and another approx 7m to dig. I know it would be better to do it on one batch, but can I fill what I have already and then dig/fill that other later? (where one wall will meet another by the way)

I'm not sure my back's up to the digging just yet you see.

Kind Regards,

 

[countygardens]

It really would be best to pour the whole thing in one go. Whatever you do other than this will cause a possible weakness.

However, IMHO if you have to stop then this will cause a 'cold joint'. Now one possible way round this is to make sure that you have some reinforcing bars sticking out of the end of your first pour so that when you come to do the second it will tie in and thus reduce the weak spot.

You can pour in the rain as long as its not pi**ing down.

hope this helps a bit. You never know, someone else might come along with a better answer in a minuite