Do I need coarse aggregate in my mix ?

[JackSpratt]

I have a four inch concrete 'slab' to lay on top of a DPM sheet (that sits on 10mm of sand).

My local Wickes sells 'Ballast' (an all-in aggregate) - will this give my floor the strength it needs at a ratio of 1:4 ? They don't sell a coarse aggregate.

The floor has to support a Mira shower tray, a toilet pan and one person !

Thanks

 

[mattysupra]

Its not ideal mixing your own concrete base for floors. I would have it pre mixed and dropped off. You can ask the company for what mix etc you want. You will get better finish as it all goes in at once rather than uneven mixes and delayed time between your own mixes.

 

[noseall]

ballast is perfect, but mix it at 6 parts ballast to 1 cement.

 

[JackSpratt]

many thanks for the replies

i'm tiling the floor with Blackstone un-calibrated tiles and very poor access to the road for anything premixed.

And it's only 8.5 cu ft

 

[mattysupra]

If its that small i wouldn't worry at all. Like noseall said- ballast will be o.k.

 

[JackSpratt]

Final check here:

How many bags of Wickes Ballast should I use for each 25kg cement ?

(They don't say how many cu.ft each bag is)

Is it all dreadfully simple and therefore six ballast to 1 x 25kg cement ??

 

[noseall]

the ratio of mix is 6 parts ballast to 1 cement.
this ratio will not change wether you use a spoon, a shovel, a bucket or even a digger bucket to gauge the mix.

25 kg's of cement will need 150 kg's of ballast added to it.

6 x 25.

 

[JackSpratt]

I didn't explain well - the bag weight/volume is unmarked. I had kind of assumed it was 25kg, but they don't say even on their web site. Anyway, I weighed a bag and indeed found it to be 25kg.

So yes, I am now the proud owner of 3 cement and 18 ballast. All in 25kg bags.