Grey concrete

[Marcgreenf]

Evening all, this sounds so silly but it's been vexing me for ages.

How do you make grey concrete?

The only concrete I've ever made (OPC & builders sand) is buff.

I want to do a pour job in the garden and would like the industrial grey you see in cast concrete, hell at this point I'll take a grey pavement finish!

Many thanks in advance.

Marc

 

[noseall]

How do you make grey concrete?

Is this a wind-up?

 

[Marcgreenf]

Sadly not.

I want to pour some walls and countertops and need them to be grey like the pre cast stuff you see.

I know if you buy it bulk and pump it it will be grey but it's not that big a job.

If you have mixed OPC and builders sand you'll know it's not grey.

Obviously I'm missing something simple but that's why I asked.

 

[kingandy2nd]

Mortar tone is what you need

 

[Marcgreenf]

Mortar tone is what you need

As simple as that?

Is that what the big cast guys use?

 

[kingandy2nd]

I don't know what the big cast guys use to be honest, probably just non-red sand.

I've just mixed a load of black mortar for my extension build (blue engineering blocks and black mortar below dpc). Basically if you use black mortar tone you get varying shades of of grey which gets darker until eventually black the more tone you add to the mix.

 

[23vc]

If you mix OPC and building sand, you get mortar.
To make concrete, which is crucially very different to mortar, you mix cement with ballast or sharp sand/aggregate. I’ve done that a lot, and it’s never not been grey.

 

[Marcgreenf]

There we go, the aggregate!

Theres no yellow sand in fine aggregate.

Like I said, simple.

Thank you very much.

 

[^woody^]

You don't use building sand for concrete. Funnily enough, you use concrete sand.