Concrete mix for internal slab - correct gravel?

[goldeagle]

I am meant to be laying a new concrete floor today in my house to replace an old floor I dug up. I really struggled to find on the internet what gravel you are meant to use in the mix, but eventually ordered some "20mm" gravel and also some pea shingle - about 850kg of the 20mm and 250kg of the pea shingle to make up the amount of aggregate I need.

However, looking at the 20mm gravel the stones are a larger than I was expecting, picking up a handfull of stones these were measuring up to 40mm.

Is this larger aggregate going to cause me a problem in mixing the concrete for the floor? Appreciate any thoughts as I am due to start mixing in a couple of hours! For information, I am planning to use a 1:2:4 cement:sharp sand:gravel mix.

 

[Jackrae]

I'd suggest they've given you ungraded material. 40mm is far too large for what you need unless your slab is going to be about 200mm thick (which it obviously isn't). Tell 'em to take it back and supply what you ordered.

 

[goldeagle]

Thanks for the reply, that's what I thought. Pain in the ass because I paid for a cement mixer this weekend to make the concrete. Attached a photo below with a £1 coin (22mm) in for reference. Assume I am right in thinking it should all be under 20mm?

Untitled

• goldeagle
• 12 Oct 2014
• 1

 

[SFK]

I am Not a builder so please let them put in their answers.

But my understanding (and what I have always used for concrete) is called "ballast". It comes pre graded with all the different sand and gravel sizes included to make a good concrete mix. For a quick look type ballast into the wickes web site.

To add that I normally make mix as a 5:1 ballast to cement.
Sfk