Another stupid question from a novice - Cement mix

[mcquitmp]

I've tried to find the information from the calculators on the site but can't quite find the right info...

I have an area which is 0.2189 cubic meters to lay with concrete. The concrete needs to be suitable for posts - judging by previous posts the mix is not so crucial but I'm trying to not overdo too much the amounts I get and still not have too little.

The actual volume of the space is 0.3105 cubic meters but I have allowed a bit for the volume of the posts.

The local merchant sells bags of ballast (20mm 20kg bags) and 25kg bags of cement.

How many required of each? Am i right in thinking 16 bags of ballast and 3 bags of cement? The calculators on site show sand, gravel and cement separately so in arriving at my numbers I jsut added the gravel and sand numbers together and assumed the ballast bags were in the right mixture.

Is that right?

Any views?

Basically my trench will be 2.3m long - 300mm wide and 450mm deep - the posts will be 120mm diameter.

Thanks...
Maurice

[lutonlagerlout]

i reckon 600kg so that 30 bags and say 5 cement
cheaper and more convenient to buy a bulk bag (normally about 850kg) and 5 cement,cost you around a nifty this way maybe a little ballast left for future stuff
btw why are you digging a trench for a fence?
correct way is a hole 300mm by 300 mm by 600mm deep
cheers LLL

[mcquitmp]

Hi,

Thanks. I'm digging a trench cos I'm laying a whole line of round posts beside each other to create a wooden feence to hold back the soil.

Maurice

[matt h]

wont the soil rot out the base of the posts so effectively negating all the work?

[Suggers]

Trees grow in soil. :p