Concrete calculations... Please check I've added up right.

[wookie]

Hi All,

I know we have good mix of trades on here, hopefully someone familiar with concreting can help me.

I've tried using a couple of online concrete calculators to work out how much All-in I need to order to make a concrete floor.

Length 9.5m, Width 4.3m, Depth 100mm

Total volume 4.085 Cubic Metres <---- (this I am fine with)

Mix amounts required are Cement 1307Kg, All-in 6.81 tonnes or 5 Cubic metres....

How can 5 Cubic metres of All-in make only 4 Cubic metres of concrete ???? WTF ????

I'm obviously being thick here, can someone please explain to me how 5cubes of All-in only makes 4cubes of concrete, so I can be happy that I will order the correct amount of All-in because I don't want to order too little, I don't mind a bit spare but I don't need a couple of tonne spare.

Thanks

 

[zzr1200]

Its a combination of the water content in the readymix and the compacted mix after leveling.

Although 5 cu metres to lay a 4 cu metres screed seems a bit over the top, but maybe the calculator only does full cu metres possibly.

 

[S-Rail]

All in ballast works out at approx 1.8 ton per cube , depending on the ballast stone , ie crushed limestone etc . As said , when mixed , the materials combine and air forced out , the cement volume shouldnt be included as part of the main conc volume , as it is so fine , it just fills the fine gaps in the all-in ballast , you may also find that if it is for a finish floor , it is worth allowing for a handful of 25kg bags of sharp sand , and allow for one shovel of it per mix , as all-in ballast often lacks enough fines which you will need to get a trowel / float finish .

cheers Sam

 

[Pete.]

I'm an expert in removing it but I've had to put some in temporarily on a few occasions as part of enabling works. All I know is if you cube up the area and just order what fits in your measurements, even with ready mixed you'll come up short. Just accept it as a fact of life.

Nowadays we use rapid readymix where they turn up with a 40 ton lorry full of ingredients and mix it in the chute. You get the mix, consistency and amount you need and there's no waste. You get charged by the volume it displays on the computer. If you can get a wagon up there I'd seriusly consider it because knocking up 5 cube with a mixer and laying it is a helluva job. It's also likely too cold to lay right now so consider that too.

 

[mike os]

Looks about right

 

[addjunkie]

Nowadays we use rapid readymix where they turn up with a 40 ton lorry full of ingredients and mix it in the chute. You get the mix, consistency and amount you need and there's no waste. You get charged by the volume it displays on the computer. If you can get a wagon up there I'd seriusly consider it because knocking up 5 cube with a mixer and laying it is a helluva job. It's also likely too cold to lay right now so consider that too.

Im in the same place here, never again will I mix it myself, even with two mixers and extra muscle 5 cubes will be a killer.

If you cant get the big waggon in there are other options. Last time we did a base used a 1 ton dumer. Also used a powered 1/2 ton dumer in the house when putting in new sub floors. Though for the big shed base we were lucy it was summer the ground hard and all 14 cubes went straight in out the lorry, though i did have a 3 ton dumper on standby.

 

[wookie]

Nowadays we use rapid readymix where they turn up with a 40 ton lorry full of ingredients and mix it in the chute.

I've used readymix before but the access is terrible and money is very tight so it'll have to be self mix and barrow in this case.

Im in the same place here, never again will I mix it myself, even with two mixers and extra muscle 5 cubes will be a killer.

Sadly I've done it before and unfortunately this time I'll have to do it again, it's casting a new concrete floor inside an existing building that has awful access.

Thanks for double checking the amounts everybody, I knew I could count on this site's members

 

[pedrobedro]

I helped a friend lay a horse stable base in a field and he had worked the amount out to the millimetre. We came up about half a cube short and had to get the mixer out to make some up. Ballast and cement is cheap compared to ready mix and you always find a use somewhere for any extra.

 

[CornishPete]

4m³ is a fair amount to mix and lay by hand. Whenever access is tight only jobs I get a pump in. Its on the back of a 7½ tonner and can pump up to 100m away. It costs about £200 to hire but here I can get readymix for about £100/m³ which is about £20-25 less than buying separate so would only work out about £100 more expensive. Factor in the time saving and also a floor is much easier to level when its all equally wet rather than trying to level as you mix and pour it one barrow at a time.

 

[mike os]

4m is bear enough 10 ton..... seriously worth considering a conveyor or pump.... I know it costs but just laying that is hard work for 3 guys, mixing laying and finishing in one pour is work for 5 men