Pouring Concrete slab

[elphingirl]

Hi all

I am hoping that someone can help me with what is probably a silly question- but it's bothering me.

We are about to pour a concrete slab 4.5m x 4.5m square, 100mm depth for a tank base. What I can't work out is how do you level it while the pour is in progress?

We'll have formwork set up to height with a dumpy, but can you actually move across the wet concrete and smooth it down?

Hope somone can help me please! Any other advice would be welcome too. We've done other bits of concrete, and are used to levelling strip footings, and curing etc - but never a slab.

Cheers
Elphingirl

[journeyman Mick]

Elphingirl,
Usually one hand on a screed, one on a shovel, driver of truck on chute.
Driver chutes in concrete close to right height, slightly over if anything, spreading it out as well as he can, pausing as neccesary to allow the screed to catch up.
Screedhand crouches down, dragging the excess concrete back towards himself into the empty section of the formwork.
Shovel hand picks up excess and spreads it into the corners that the chute won't reach.

The workers walk in the formwork, through the unfinished concrete, but stay off the screeded section.

Once the form is full, truck hosed off and gone, screed washed then if the concrete is set up enough floating can begin. with a slab of 4.5 x 4.5 you won't be able to reach into the centre of the slab with a hand held float, so there's two options:
1) hire/buy/beg/borrow/steal a bull float. This is a mag float on a long pole. twisting the pole changes the angle of the float relative to the handle so you can prevent it digging in.
2) stack some concrete blocks up next to your fromwork and lay an ally plank over the top of the concrete. Walk out along this and float by hand.

As it's only a tank base you won't really need to trowel it as well, but if you do, you can carefully walk on the slab by this stage.

Have fun! I absolutely hate working with the stuff and nowadys simply fib and tell people I can't work with concrete. (Actually, I' not really fibbing, my back certainly can't stand it anymore, so I can't really work with it)

Mick

[elphingirl]

Thank you so much Mick for your reply - I feel better already (of course I can't actually do any of the work - being 6 months pregnent).

I like the idea of the ally plank - we have some nice 5 metre pieces of Oregon lying around - they'll do a great job.

It's not good on your skin, but it's still pretty fun to deal with in a sort of child-in-a-sandpit way (until it starts to go off before you've finished).

Cheers
Justine

[Wombat2]

What sort of tanks are you installing? If iron then an old tank maker friend always installs his on corrugated iron. Cuts down on the condensation build up between the base and the slab and delays the bottom rusting out.

Actually with our 4 x 5000 gallon tanks we didn't even use slabs We laid 3 rows of old railway sleepers on some bedding sand nice and flat and level then laid the iron and tanks on top. Stayed like that for over 10 years before we moved and as far as I know they are still there.

David L