Small foundation 1.30m x 1.10m - experiences?

Hello,

I need a small foundation, approximately 1.30 x 1.10 m.
A device (weight approx. 400 kg) is to be placed on it and secured to the ground with four screws. Hence the foundation.
Both the device and the foundation are exposed to weather conditions, but the device can get completely wet.

I would now excavate the whole thing, lay about 10 cm of gravel, and then fill it with about 15 cm of concrete. I would omit the steel mesh.
The whole thing with wooden formwork, for which there are so-called release agents.

Are 10 cm of gravel and 15 cm of concrete sufficient? Or is that too much for the stated purpose?
Do I need to compact the gravel layer? I don’t necessarily have a vibrating plate at hand.
For concrete, I would have used 40 kg of concrete screed from the hardware store.

What is your opinion on the whole project?

Best regards

I am not an expert in the field, but I would be afraid of "breaking" the 15cm thick concrete with the anchors (which anchors/screws should go in there?) when fastening the device - especially because there is no reinforcement inside. Does the foundation only have to bear the load, or does this machine also move? I would definitely compact the ground a bit, even if only with a paving stone and a rubber mallet.

The machine does not move. The foundation is simply there so that the device can be fixed to the floor and cannot be "tipped over." I cannot say exactly what kind of screws go in there, as the device is not yet there and these are supplied.

The planning for the foundation is not correct as it is.

You should excavate about 60 cm, depending on soil conditions. Maybe even 80 cm deep.
Add a frost protection layer, preferably using coarse lime gravel, and compact it thoroughly with a tamper or vibrating plate.

On top of that, a construction foil. Then build formwork from boards. You don’t need a release agent there. A thickness of 15 cm is sufficient, with steel reinforcement 10 cm is enough. I would definitely include steel reinforcement. Without it, the concrete slab will crack sooner or later. More likely sooner.

Without foil, moisture will always rise from below. A bit of gravel underneath won’t help either; frost will push the concrete slab upwards and it will break. The substructure must be right.

As soon as you pour concrete, you have a rigid layer on top. Then you also have to establish a frost-resistant foundation, otherwise, you will get cracks in the medium term. Depending on the soil, this is then 40-80cm. You also have to compact the gravel/scree layer. The space for a vibrating plate is quite tight, but you can rent a trench tamper for half a day for little money.

You should dig about 60 cm, depending on the soil conditions. Maybe also 80 cm deep.
Put in a frost protection layer, best to use coarse lime gravel for that and compact properly with a tamper or vibrating plate.

Then a construction foil. After that, build a formwork from boards. You don’t need a release agent there. A thickness of 15 cm is sufficient; with steel reinforcement, 10 cm is also enough. I would definitely include steel reinforcement. Without it, the concrete slab will crack sooner or later. More likely sooner.

Without foil, moisture will always rise from below. A bit of gravel underneath won’t help either, frost will push the concrete slab up and it will crack. The substructure has to be right.

Thank you very much. Phew, okay. I had hoped it would be easier. I have to say that the foundation is not on my property, but rented, and it doesn’t have to last forever. It’s only about securely fastening the machine.

Do you really think I still need 60 cm?

With steel reinforcement, I would be afraid that with 15 cm concrete, I would hit it exactly with the screws when fastening the machine.

As soon as you pour concrete, you have a rigid layer on top. Then you also have to build frost-proof, otherwise you will have cracks in the medium term. Depending on the soil, that’s 40-80 cm. You also have to compact the gravel/crushed stone layer. For a vibrating plate the space is rather tight, but you can rent a trench tamper cheaply for half a day.

Cracks wouldn’t bother me personally. First, you don’t see them when the machine is standing on it, and second, it doesn’t have to last forever. As said above, it’s only about fastening the machine.
Right next to the location is a hardware store, they offer a tamper for rent.