Forming and casting slabs yourself - experiences?

Hello abc

I would do it like this: every 30cm vertically 12mm reinforcing bars into the formwork blocks, 15 to 20cm deep and 10cm protruding at the top. About 7-8cm above the formwork blocks a 12mm reinforcing bar to connect the rods along the entire length. Formwork at the bottom and sides. Then every 20 to 30 cm crosswise 12mm reinforcing bars the whole length. Spacer pieces on top and a cut-to-size steel reinforcement mesh on top. Anchor everything well. (If electrical wiring needs to go in, now would be the right time). Then mix concrete (1:3.5) with 2 to 3 buddies and pour a ceiling at least 20 cm thick. That should hold. As I said, I would do it like this (and have already done it this way). But with work like this, everyone is responsible for themselves. The structural engineer does nothing different, just more delicate. And the concrete mix should of course be well mixed. Not sometimes 1:4, then 1:3 again. The mixer really has to concentrate.

Steven

Hello

sorry, I just noticed that the ceiling I specified is not quite suitable.
So: the first area is 2 x 1.5 meters.
The second 2 x 2 meters.?
And there has to be an opening for a manhole cover in each?
The rebar should be bent. 5 cm to the edge of the manhole cover. Otherwise: more is better. Put in good reinforcement and possibly 30 cm of concrete. Make the concrete nice and thin and tamp it properly.

Steven

Hello Steven, thank you for your response. Since the concrete formwork blocks are completely concreted, I can do it all in one pour then. I have 6m long 14mm reinforcement bars here. I will bend them accordingly and then twist everything directly into the formwork blocks.

I will have the concrete for filling the formwork blocks delivered ready-mixed, that means it only needs to be moved into place. There are no differences in the mixing ratio then. For vibrating the ceiling, I will get a needle vibrator so that the air is nicely removed.

Then the ceiling and blocks are basically cast together... that should provide even more stability since it is a composite.

Thank you very much for your tips.

can I do it all at once then.

Hello abc

don't imagine it to be that easy.
How high will the formwork blocks be stacked? The cavities in the blocks are somewhat intricate due to the crossbridges. And there’s still a lot of rebar in there. You have to get the concrete all the way down. Air pockets would be really bad.
Plasticizer in the ready-mix concrete is a must.
How will the concrete be delivered? Pumped in directly? That works. But parking somewhere and then bringing it over with a wheelbarrow, I don’t see that going well.
How many cubic meters of concrete are needed? If it’s no more than 2 or 3 m³, you can do it yourself on a Saturday with 2 to 3 buddies.
You also have to fix the formwork blocks well. They just lie horizontally on top. They tend to shift during pouring. Not good at all.
If you mix the concrete yourself after all, I would create the walls and the ceiling on 2 separate days. The entire formwork and reinforcement is very complicated. If the walls are already stable, the ceiling is easier.

Steven

Hello

me again:
You don't bend 14 gauge iron. Not by hand.
Use 8 gauge or 10 gauge (if you can still bend 10 gauge).

Steven

I already have the 14-gauge iron here for reinforcing the walls. I bend it in the vise. With the power of physics (leverage), it works.

The shuttering blocks reach a final height of 2m but are intermediate concreted at a height of 1m to prevent them from slipping. Unfortunately, you can't get a bottle vibrator into the blocks, so you just have to poke inside. The filling is not done with the pump but by hand. That means ordering ready-mix concrete with a retarder and then shoveling it in with a few buddies on a Saturday. One person is always by the blocks, poking and tamping the concrete into them. A total of around 11m3 of concrete is needed for the blocks, meaning about 5.5 m3 over two trips... mixing that additionally by hand and I might make new friends... I don't want to do that to them or to myself. This way, you also have consistent quality.

I had a pump for the slab with 14 m3 of concrete, and it cost me 450 euros... so for 2 deliveries, that would be 900 euros, which I can invest better.