Concrete floor for water tank. Some questions.

[Com_VC]

I'm going to be doing a concrete floor for a water tank to sit on. The size for this will be 2.1 x 2.1 metres and 100mm thick. I will be boxing it all up and using F72 reo.

I've calculated the amount of concrete required and it came to .44 cubic feet. That is if my calculations are correct.

Just a few questions.

Will treated pine be suitable for the boxing, we have some at work and I think it's around 25mm thick. I was just planing to nail it all together and then remove the lot when the concrete is finished.

Is that reo suitable, we just had a slab done for a steel shed and that was what was used.

Should I use concrete pre mix bags or cement bags and I think you add crushed rock, sand etc?

How do you work out how many bags are required.

Pretty new to this but am willing to learn.

Thanks

[Vernonv]

I've calculated the amount of concrete required and it came to .44 cubic feet. That is if my calculations are correct.

No, it's 0.44 cubic metres

Will treated pine be suitable for the boxing, we have some at work and I think it's around 25mm thick.

Just use plenty of pegs to support the boxing - concrete is surprisingly heavy.

Is that reo suitable, we just had a slab done for a steel shed and that was what was used.

Yep should be fine

Should I use concrete pre mix bags or cement bags and I think you add crushed rock, sand etc?

I would buy the cement and all-in (sand/aggregate) and then mix on site, but it is personal preference (doing it this way is normally cheaper).

How do you work out how many bags are required.

8 x 20kg bags of cement (16 per m3) and 0.6m3 of all-in (1.3 per m3)

Premixed bags (I think) work out to about 44 x 20kg bags

[Com_VC]

Hi,

Can you give me an a rough idea on the cost?

Also will it be the same strength as using pre mix which I believe is 20mpa?

I bought 5x premix bags the other day at $8.50 each. I'm guessing this way would work out much cheaper?

Thanks

[Terrian]

Hi,

Can you give me an a rough idea on the cost?

Also will it be the same strength as using pre mix which I believe is 20mpa?

I bought 5x premix bags the other day at $8.50 each. I'm guessing this way would work out much cheaper?

Thanks

real rough cost for .5m3 is about $40 for sand & stone, and about $50 for cement, 20mpa is 12 x20kg bags per m3, I am not 100% sure, but I don't think the bags of pre mix are 20mpa (been too long since I was in the game

[Com_VC]

What mpa would be required?

Also with the shed we had to have a 50mm sand bed underneath the concrete, would this be required?

Should I use a plastic membrane as well?

[Vernonv]

Hi CVC,
Terrian's estimates are probably pretty good.

I think the tank manufacturers specify 20mpa be used. Don't know about the sand bed, but when I did mine (I've done 3 in the last 6 months), I didn't use a sand bed but I did use plastic. One of the benefits of plastic is that it helps reduce water loss from the concrete during curing.