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Author: Subject: Concrete mix - volume or weight
smart51

posted on 20/5/16 at 08:09 AM Reply With Quote
Concrete mix - volume or weight

I'm going to build a play shed in my garden for my son. It will need to be built on brick piers so its at the right level at the front, so I'm going to dig a pit at each corner and fill with concrete.

Google suggests a 1:2:4 mix of cement, sand and aggrigate. Is that by weight or volume?

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joneh

posted on 20/5/16 at 08:25 AM Reply With Quote
Most footings I've done are a 1:4 shovel full using cement and ballast. Generally measurements are volume.

Can't see a builder with a set of scales!

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nick205

posted on 20/5/16 at 08:26 AM Reply With Quote
For concrete I tend to work by shovel fulls of each trying to get the volume roughly right (particularly when using a concrete mixer) then just add water and a little Febmix (plasticiser) until you get the runny-ness (sp?) you want. From what you describe I'd imagine you want it quite runny so it will level itself when the holes are filled. Be aware it may take a while to dry/harden before you can build onto it.






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Mash

posted on 20/5/16 at 08:28 AM Reply With Quote
For what you're building it's not massively important Mate, as it's not carrying huge amoun ts of weight, but this web site is really useful:-

Concrete calculator

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Slimy38

posted on 20/5/16 at 08:28 AM Reply With Quote
I asked this exact same question a while back, and the response was 'put yourself in a builder shoes, what will you have available?'.

As joneh says, a builder won't be carrying a set of scales around on site, but he will have plenty of 'shovelfulls'.

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smart51

posted on 20/5/16 at 08:46 AM Reply With Quote
quote:
Originally posted by Slimy38
I asked this exact same question a while back, and the response was 'put yourself in a builder shoes, what will you have available?'.

As joneh says, a builder won't be carrying a set of scales around on site, but he will have plenty of 'shovelfulls'.


I was thinking in 25kg bags, which is what I'd buy from the shop.

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smart51

posted on 20/5/16 at 08:52 AM Reply With Quote
quote:
Originally posted by Mash
For what you're building it's not massively important Mate, as it's not carrying huge amoun ts of weight, but this web site is really useful:-

Concrete calculator


Good site. For a 25kg bag of cement, it recomends 47kg of sand and 94kg of aggrigate. I reckon thats 1:2:4 in terms of volume, as it's a bit less in terms of weight. As you say, it's not critical for my application.

quote:
Originally posted by nick205Be aware it may take a while to dry/harden before you can build onto it.

Its a several weekend project. The concrete will get its 28 days to cure before the job is finished.

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on_eighty_runner

posted on 20/5/16 at 09:10 AM Reply With Quote
I did something similar with a playhouse and got in bags of cement, mixer and a trailer of gravel.
A lot of cleaning up and hassle

When I did a deck I bough bags of postcrete- a bag of dry mix you dump into your predug hole filled with water.
It's s bit more expensive but no cleanup and for a lightweight application is probably good enough.

Alternatively look around for a builder who is already working locally and set up for a job ask him/her.

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smart51

posted on 20/5/16 at 09:16 AM Reply With Quote
quote:
Originally posted by on_eighty_runner
I did something similar with a playhouse and got in bags of cement, mixer and a trailer of gravel.
A lot of cleaning up and hassle

When I did a deck I bough bags of postcrete- a bag of dry mix you dump into your predug hole filled with water.
It's s bit more expensive but no cleanup and for a lightweight application is probably good enough.

Alternatively look around for a builder who is already working locally and set up for a job ask him/her.


Bags of post fix would only work out £20 more expensive, so probably not a bad idea. But there's a builder on site doing other work. He leaves his cement mixer in the garage over the weekend. I've spotted an opportunity

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nick205

posted on 20/5/16 at 09:24 AM Reply With Quote
A good call if you've got a mixer available to you - that will save a lot of time and back bending!

I laid a concrete base for my shed a few years back. Probably spent as long barrowing and leveling the hardcore as I did mixing and leveling the concrete. I set a slight slope on it to help any rain water run off it and it's been fine for 10 years now (the shed itself is crap, but cost £150 so can't really complain).






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garyo

posted on 20/5/16 at 10:58 AM Reply With Quote
Most important is to make sure that shovel=shovel. Cement has a tendency to stack massively on your spade whereas sand, especially if dry, can end up with half the amount. If you're not careful you can easily end up with 1:3 just through shovelling error.

[Edited on 20/5/16 by garyo]

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SteveWalker

posted on 20/5/16 at 11:14 AM Reply With Quote
I think buckets or half-buckets are easier, especially when loading up a mixer. Less twisting and lifting, easier to measure.
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cliftyhanger

posted on 20/5/16 at 03:40 PM Reply With Quote
Mixer and bags.....
should be easy, chop cement bags in half with a handsaw, 1 bag of sand, 2 of ballast (or whatever) will be close enough.

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Mash

posted on 20/5/16 at 06:39 PM Reply With Quote
Built a 10 metre long by 1.5 metre high double block retaining wall back in 2008.

75 mm cavity between the blocks, and a 1 metre x 200 mm foundation.

All the concrete was mixed in my mixer using the calcs from the web site I linked to, and I measured it using the trusty bag method mentioned by the other guys.

It's still standing, hasn't moved an inch, and is holdin up the farmers field quite well

[Edited on 20/5/16 by Mash]

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mark chandler

posted on 20/5/16 at 08:29 PM Reply With Quote
1/2 bag of cement, 6 decent shovels of ballast and 1/2 bucket of water into my mixer produced a nice strong concrete slab.

If mixing up for pointing/brick laying then you need to be precise for the same colour mortar across the job.

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smart51

posted on 22/5/16 at 07:44 AM Reply With Quote
It' sd one. Thanks every one. I put two bags of aggregate and one of sand in the mixer and it looked very stoney. I was a bit worried by by the time it was lured it was great. I under estimated quantities somewhat. Probably because the sandy, cement and water fills the voids between the stones. Two of the brick piers are built -and level with each other! I'll odo the other two this afternoon.
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