Concrete Mix Advise!

[Damo636]

I have lined out a 12'x12'x4" deep plot in the field at the back of the house that I plan to concrete as an observing deck. I am wondering what ratio to mix the concrete mix /cement. I am guessing 4-1 or should I go stronger?

[Nillchill]

the mix I was taught many years ago was a 4-chippings 2-sand and 1-cement. It has always served me well.

[Bizibilder]

There are quite a few concreting / DIY websites you could try. I think between 4;1 and 6:1 is about right if you are using ballast (sand and stone mix) You have to be careful if using sand/stone/cement seperately to get the mix right. Also the amount of water is important- believe it or not!

[Damo636]

Thanks guys, much appreciated. It is already premixed sand and chip so I shouldn't be too far away at 4:1.

[Islander]

There's a wealth of information on concrete and other stuff on the paving expert site. Here's a link to concrete specs:

Paving Expert - AJ McCormack and Son - Mixing Concrete

[swamp thing]

4:1 what are you building a U Boat pen.

Good grief it's only a telescope platform, 6:1 would be ample.

Regards Steve

[Damo636]

I suppose it could double up as a heli pad Steve

[ollypenrice]

Listen to the builders. I do 5 to 1 but I'll economize next time, on reading Steve's post above.

On readymix, though, one caution. If it gets left out in the rain the sand gets washed to the bottom and you get an uneven mix if you're not careful. I had some that had suffered this fate at the builders' yard and got a very chunky base for my otherwise rather smooth Takahashi mount!

Olly

[Damo636]

Listen to the builders. I do 5 to 1 but I'll economize next time, on reading Steve's post above.

On readymix, though, one caution. If it gets left out in the rain the sand gets washed to the bottom and you get an uneven mix if you're not careful. I had some that had suffered this fate at the builders' yard and got a very chunky base for my otherwise rather smooth Takahashi mount!

Olly

Advise taken on board Olly, cheers.

[Peter Drew]

That's quite a bit of concrete to mix even with a mixer, make sure you tamp it down level as you go along. If you leave this untill last, the first mix might well have set by then.

[Tiddles]

Ballast , 6:1 will be fine. I built a 14' x 12' shed base with it and added a couple of sheets of mesh. 3 tonnes was a lot to mix.....even with a mixer!!

[pete_l]

That's quite a bit of concrete to mix even with a mixer, make sure you tamp it down level as you go along. If you leave this untill last, the first mix might well have set by then.

That's what happened to me when I was building my patio (5m x 5m).

I was using a mixer and there was only me to do all the work. By the time I have mixed up a dozen or so loads and laid them for the base, the first ones were a lot stiffer than the last. Made leveling it all a bit tricky. I'd assumed it would remain "liquid" for at least a day

BTW, cement is cheap, the amount you'd use between a 4::1 and a 6::1 mix probably won't amount to a hill o' beans.

[Damo636]

We are going to tackle this now shortly, just waiting for the help to arrive. I have two brothers and going to work them to the bone for a few hours I estimate around 20-25 wheelbarrow fulls.

[sparkly]

6-1 should be ok but if your a novice you might get a sandy surface,

alot of folk put 6 heaped shovels of gravel/sand mix and 1 level cement mix in theory thats a 8 to 1 mix, if it were me and i wanted a good hard surface i would go 4-1 mixed tamped and floated properly will give you a good hard long lasting surface.

[Ibbo!]

At 12 x 12 you may get the dreaded 3m crack I would be tempted to do it in 4 sections that way the joins will be where you want them

or you could go all tech and use crack inducers(in other words a length of wood in a triangular shape)placed on the bottom

A nice sticky mix

in other words not too much water

a good tamp and do not over work the surface

Steve