9 Apr 2010
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United Kingdom
Hi guys,

I'm doing a pond base which will be 3.3m x 2.3m x 250mm depth.

I have phoned around and got a price of £350 for the concrete and £300 to have it pumped. (2 cubic metres)

Now my question is how many bulk bags of ballast and cement do I need to mix it myself? I am after a very strong mix equal to C35

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Thereabouts. Shade more than 2.5 jumbo bags though - more like 2.7 (so three really!) For a strong mix (C35 ish) you'll also need sand.
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Its probably worth trying to mix a retarder in if you must hand mix. Even with help it may take a good morning and you'll end up with a stiff hard to level slab curing at all sorts of different rates.

The workability is especially important if it has a bottom drain and needs grading and finishing down to it
Sorry, I should have said aggregate, sand and cement. (not all in ballast) You could make concrete from all in ballast but you won't get 35N. To get 35N you would need a more precise mix and the only way to get that is agg, sand, cement. All in ballast varies too much.

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