ᐅ Foundation – How deep does the excavation need to be at minimum?

Hello everyone,

I urgently need expert advice as I am quite inexperienced in this area.

Here is the situation:

I would like to build a 2m x 2m (6.6 ft x 6.6 ft) foundation on my property. First of all, I live in a remote area in Africa where the soil consists entirely of sand. You can easily dig one meter (3.3 ft) deep without hitting a single stone. However, the soil becomes quite compact at a depth of 30 cm (12 inches), so it’s not like sand dunes. I need a firm base that I can walk on without sinking :p. Apart from my own weight, the foundation doesn’t need to support any other loads.

I have gravel, cement, and sand. But most of all, I have no idea how to build this.

Here are some questions I’m asking myself (and you):

How deep should I excavate this area?
Should I first put gravel in the hole to stabilize the ground?
What should the gravel/cement mixing ratio be to ensure stability?
How long does it take to cure, considering daytime temperatures of around 40°C (104°F)?

I hope these questions are not too silly. As I said, I have no clue!

I’m grateful for any tips. I probably have missed important points as well.

Thanks in advance for your help.

Best regards,
Paulus

Hello Paulus,

If you are mixing the concrete yourself, use gravel with a grain size of 0/16 and Portland cement PZ 35 in a mixing ratio of 4 parts gravel to 1 part cement. Of course, water is also needed. The water-to-cement ratio (measured in grams) should be about one to two. For example, with 10 kg (22 lbs) of cement, this corresponds to 5 kg (5 liters) (11 lbs / 1.3 gallons) of water.

6Richtige schrieb:
Hello Paulus,

if you mix the concrete yourself, use gravel with a grain size of 0/16 and Portland cement PZ 35 in a mixing ratio of 4 parts gravel to 1 part cement. Of course, you also need water. The water-to-cement ratio (measured by weight) should be about one to two. For example, with 10 kg (22 lbs) of cement, that corresponds to 5 kg (11 lbs) or 5 liters (1.3 gallons) of water.

Hello 6Richtige,

Thank you for the prompt reply! The mixing ratio is clear now (yes, I have water too 😀 ).

Do you (or anyone else) perhaps have any tips or comments regarding the other points?

Curing time: Approximately 1 week, do not forget to keep the slab moist to prevent cracking.

Depth: The base should be made of material that allows water to drain, such as gravel or similar, and be well compacted. The slab should be about 10–20 cm (4–8 inches) thick, depending on the intended use. It obviously does not need to be frost-resistant 😉 Steel reinforcements to prevent cracking are also beneficial.

🙂 Thank you 6Richtige,

that would settle everything.

And here we go...