How do I know how much concrete I need?

[Tas_Dean]

Hi All,

I have to fill a hole in a slab, the hole is about 2m long, 1m wide and around 100mm deep. I intend to buy some gravel and cement and concrete the hole up myself. How do I work out how much gravel I need?
It's non-structural, indoors and will only have foot traffic on it, no need for reo.

Cheers, Dean

[scooter]

Dean, don't take this as gospel, just a quick nut out.

My guess would be your hole is 2x1x0.1m = .2 cubic metres

I think a basic concrete mix is 3:2:1 sand stone cement.

So the stone would be 1/3 of the mix which would be .06 cubic metres.

Wait for an informed opinion.


Cheers................Sean

[DavidG]

The sand almost fits in between the stones.
Same with the cement.
so you need almost .2cu m of gravel and of sand
or .2cu m of sand and gravel mix
always get a little more as it is a pain it the ... to be a little bit short.

[ozwinner]

What Scooter said, but double it, once it all gets wet and the sand and cement hides in the rocks you wont have enough.

Al

[pawnhead]

I think a basic concrete mix is 3:2:1 sand stone cement.

It's more like 3 stone, 2 sand, 1 cement.

You order it by the tonne, but in the yard they usually just guess how much a tonne is when they scoop it up with their tractor.
Here's a calculator.
Plug in "0.2 m3" and you get about 1/4 tonne of sand, 1/4 tonne of gravel, and 4X 20kg bags of cement. I'm sure they'd scoop up a bit more than your order so you'll probably have a bit of material left over to get rid of somewhere.
Then again, 0.2m3 isn't a whole lot, so they might just sell it all to you in bags which would be a bit more expensive. The cheapest way would be to just bring your own trailer or ute, and just shovel in whatever you need. Use a tape to "guestimate" the volume of each.

[Tas_Dean]

Thanks for the replies guys, the hole is now full. The local concrete supplier (as in concrete trucks) sells concrete gravel, which already has the sand mixed in. Told them I needed about 0.2 Cu meters, and he jumped in the loader and dropped half a bucket on. He told me it might not be quite enough, but as it has been phissing down with rain for a couple of days now, he wouldn't put any more on my poor old trailer, she was sitting on the spring chocks as it was. There was about 3/4 of a ton of wet gravel!

He knew how to estimate, I needed about 4 more shovelfuls than I got!

[pawnhead]

I needed about 4 more shovelfuls than I got!

A few brick batts would fix that.

[Terrian]

It's more like 3 stone, 2 sand, 1 cement.

You order it by the tonne, but in the yard they usually just guess how much a tonne is when they scoop it up with their tractor.
Here's a calculator.

Much more likely to be sold by volume rather than weight (worked in garden /concrete supplies for 12 years )

roughly .75 m3 stone, .65 m3 sand, 240kg cement to make a 1 m3 of 20mpa

[Blocklayer]

This concrete volume calculator might help you calculate concrete volumes for slabs. It has options for different shapes, perimeter and internal thickenings as well.

http://www.blocklayer.com/Concrete-Calculator.aspx

Its been a while since I mixed concrete by hand (mixer) but we just got premixed stone/sand

[kekemo]

When you work out what you need, before you make it up, check to see if you need to cement anything else, do you need to move the hills hoist, do you need to put some cement under the drain pipe out the side of the shed....need some cement to make sure the brick pavers don't move sideways in the winter..... perhaps get the grandkids/kids to put feet marks in the garden.....lol
then you can easy calculate it by making twice as much as half the amount you need.....
does that help.....
have a great day!
kindest regards KEKEMO......