Cheap Conrete Mix?

[adbert]

Does anyone know where we can buy concrete mix cheaper than from Bunnings? I think Bunnings is selling 20kg bag for around $6.25.

[Master Splinter]

Buy bags of cement and a trailerload of sand/gravel mix from the local landscaping yard. Way cheaper.

[adbert]

Argh you just reminded me of something. I still have unused tons of gravel from my garden, should mix them up with cement to turn them into concrete mix. I'll be re-stumping my house so I'll need lots of concrete mix for stump footings. Thanks. But don't know if this will be the same as pre-mixed concrete sold in stores though.

[stevoh741]

1m3 by bunnings bags costs approx $1000, 1m3 by truck $200ish, 1m3 sand/gravel/cement (and mixer) from landscaper $130ish. I know what I'd be using.....

[adbert]

Would garden gravel suitable for concrete mix for footings? I don't know what my unused garden gravel is called but they look like honeycomb sandstone.

[Bedford]

If you can post a reasonably close up pic of what you have, that will help to answer your question.

[adbert]

86860

I think they're called Scoria. Now thinking about them, don't think they're suitable as concrete mix.

[stevoh741]

Scoria is the right size but as we don't get it in qld couldn't comment
On strength in concrete. If it was only going in holes I'd
Probably use it.

[adbert]

I feel they won't last - absorb water/damp and will break up. Hence, weaken the concrete.

[PeteV]

blue metal is what you usually find in concrete. the sand required is a washed sand. a description on what parts are required are written on your cement bags.
hope this helps!

[Cementer]

be very careful using scoria, may not survive the test of time. As PeteV says, blue metal or river gravel better option. If it was my place, I wouldn't be using it that's for sure.

[adbert]

Thanks guys. I won't be using it in my concrete mix :)

[Ken-67]

Get the concrete blend from landscape supplier, cement bags wherever cheapist, hire concrete mixer. Save money, get good excercise:2tsup:

[adbert]

Yeah I'll do that. I think some landscape suppliers also supply dry concrete mix (not in bags). Probably it's sold by cubic metres.

What's about vocanic gravels, do you think they're suitable as concrete mix?

[Master Splinter]

The compressive and shear strength of the aggregate is what gives concrete a lot of its strength, so really you'd have to know the details of that for your gravel to see if it is suitable for your intended application. If local suppliers aren't using it that's probably an indication that you shouldn't, either.

TL:DR - It'll probably be more expensive to consult an engineer about it than you will save by using it.

[Ken-67]

Volcanic gravels are usually used for making lightweight concrete for uses such as concrete boats. I'm not sure how it would go as a structural concrete, but I would imagine that volcanic gravel would be a lot more expensive.
I'd be sus of a dry mix not in bags. It would be susceptable to atmospheric moisture, so the curing process would have already started before you bought it.

[PeteV]

ken, the dry mix comes without cement in it. you add the cement as you mix it. also, volcanic gravel is usually about half the price of blue metal. the scoria shown in the photo several posts earlier is an example of volcanic rock. also, lightweight concrete is usually made by adding a plasticiser to the concrete. this is so that the concrete "holds" air in the mix. they don't use volcanic rock in lightweight concrete. light weight concrete is also used for some precast panels. hope this helps!

[adbert]

Thanks guys. Very informative and educational.