C20 concrete mix
Dean
After considering the much appreciated advice given here, I've now decided
to bite the bullet and pour a concrete base for my shed.
AIUI C20 is a suitable mix.
If I use all-in ballast, would I need to mix 1:5 or 1:6?
As far as quantities go, it's about 0.75m3. So, if using say 1:5, I'd need:
50 x 25Kg all-in ballast
10 x 25kg bags of cement
Does this sound about right?
John Rumm
> After considering the much appreciated advice given here, I've now decided
> to bite the bullet and pour a concrete base for my shed.
>
> AIUI C20 is a suitable mix.
> If I use all-in ballast, would I need to mix 1:5 or 1:6?
1:6 IIRC with all in one ballast:
http://www.pavingexpert.com/concmix1.html
> As far as quantities go, it's about 0.75m3. So, if using say 1:5, I'd need:
> 50 x 25Kg all-in ballast
> 10 x 25kg bags of cement
>
> Does this sound about right?
If you say 1m^3 is 1800kg of ballast, and 320kg of dust, then 0.75
should be 54 x 25kg bags of ballast, and about 8 x 25kg of cement.
--
Cheers,
John.
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Dean
>Dean wrote:
>> After considering the much appreciated advice given here, I've now decided
>> to bite the bullet and pour a concrete base for my shed.
>>
>> AIUI C20 is a suitable mix.
>> If I use all-in ballast, would I need to mix 1:5 or 1:6?
>
>1:6 IIRC with all in one ballast:
>
>http://www.pavingexpert.com/concmix1.html
>
>> As far as quantities go, it's about 0.75m3. So, if using say 1:5, I'd need:
>> 50 x 25Kg all-in ballast
>> 10 x 25kg bags of cement
>>
>> Does this sound about right?
>
>If you say 1m^3 is 1800kg of ballast, and 320kg of dust, then 0.75
>should be 54 x 25kg bags of ballast, and about 8 x 25kg of cement.
Thanks John.
bolt...@mailbolt.com
Check that 2 big bags of ballast isn't cheaper, though.
meow...@care2.com
The densities are different and the usual ratios are by volume, not
weight.
NT
robgraham
See if you can find a contact that will get you the tail end of a
mixer load. You've got a reasonable amount of concrete to mix there,
even if you use a mixer and some friends. OK I've done bigger volumes
on a manual basis but then I was young and foolish. It cost me £90
for 1 m^3 the other day with it being shot straight through the hedge
onto the site so I had no barrowing, no storage, no beer to give
friends, no backache, etc, etc and it was all done within an hour.
Beware of course that you may only get half and hours warning.
Rob
Andy Wade
> 1:6 IIRC with all in one ballast:
No, C20 is 1:2:4, or 1:4 with all-in ballast. 1:6 will only give you a
C7-ish mix, too weak for slabs and bases.
For 0.75 m^3 of C20 the calculator at
http://www.pavingexpert.com/calccon1.htm reckons you need 240 kg of
cement, 473 kg of sand and 878 kg of gravel. Adding the last two gives
1351 kg of aggregate. I'd order 10 bags of cement and 1.5 tonnes of
ballast (plus a big mixer, plenty of beer and a few friends to help).
--
Andy
John Rumm
> John Rumm wrote:
>
>> 1:6 IIRC with all in one ballast:
>
> No, C20 is 1:2:4, or 1:4 with all-in ballast. 1:6 will only give you a
> C7-ish mix, too weak for slabs and bases.
Not sure I follow that...
My understanding was that 1:2:4 was 1 part cement, 2 parts fine
aggregate, and 4 parts coarse aggregate.
So if you are using ballast (which is the coarse and fine aggregates
mixed in about the right proportion), then that worked out at 1 part
cement to six ballast?
> For 0.75 m^3 of C20 the calculator at
> http://www.pavingexpert.com/calccon1.htm reckons you need 240 kg of
> cement, 473 kg of sand and 878 kg of gravel. Adding the last two gives
> 1351 kg of aggregate. I'd order 10 bags of cement and 1.5 tonnes of
> ballast (plus a big mixer, plenty of beer and a few friends to help).
So 54 bags of ballast at 1350kg, and 8 bags of cement at 200kg - sounds
like the same ballpark?
(we agree on the quantities of beer, friends and mixers though)
The Medway Handyman
Andy Wade
> Not sure I follow that...
>
> My understanding was that 1:2:4 was 1 part cement, 2 parts fine
> aggregate, and 4 parts coarse aggregate.
Yes.
> So if you are using ballast (which is the coarse and fine aggregates
> mixed in about the right proportion), then that worked out at 1 part
> cement to six ballast?
No. When you mix 2 vols of sharp sand and 4 vols of gravel the result
is (not much more than) 4 vols of ballast. The sand fills the gaps
between the stones and doesn't bulk out the overall volume very much.
Therefore when using ready mixed (all-in) ballast the mix is 1 of cement
to 4 of ballast.
By the same argument your 1:6 mix is equivalent to 1:3:6 ('foundation mix').
--
Andy
John Rumm
Fairy nuff...
Ah yup, just spotted the error in my sums - I did the sums based on
weights required to make a cube of concrete rather than volume, which in
theory should have arrived at the right quantities - however at the last
step calculated the cement on the 1:6 ratio rather than just multiplying
320 by 0.75.
Roger
from Andy Wade <spamb...@maxwell.myzen.co.uk> contains these words:
> John Rumm wrote:
> Yes.
My ancient (1965) Collins Architects and Builders diary has it that
1:2:4 is the same as 1:5 ballast. It has 1:2:3 as equivalent to 1:4 1/4.
FWIW I have just had delivered 2 tonnes loose of Ballast and 12 bags of
cement as the first stage of reworking my 1 in 4 alternative exit. I had
intended to use 1:6 as I was under the impression that that was what
McCormack recommended.
In the past I have used 1:2:5 for floors but am fairly sure that was a
bit wasteful of cement.
--
Roger Chapman