Base plate - gravel underneath or not

Hello everyone,

In my soil report, it is recommended to "lay" a layer of gravel below the foundation slab because the soil conditions are not very good (waterlogged). The basement will be constructed as a [white tank].

Now the general contractor suggests omitting the gravel layer because, from his point of view, the benefit is lower than the risk that the gravel could gradually be washed away by water (slight slope) and this could possibly lead to cracks (eventually). The general contractor has no financial interests, as it is not included in his fixed price anyway. The contractor told me that there is apparently a kind of "war of beliefs" – some say one thing, others another. The argument that small stones under the house are washed away over the years by water makes sense to me.

My general contractor will also consult with the soil expert again.

I just wanted to ask for opinions here in the forum – maybe someone can say something about it.

Best regards Oliver

I really can't help you, others have to do that. BUT: I wonder where the small stones under the house are supposed to go? The gravel is compacted in layers and filled around it and also compacted. If there is a risk that something could be washed away under your house, then I would generally ask myself whether it should really be my property

By the way, I have never heard that one can do without the gravel base under a slab on which a single-family house will stand. But you never stop learning.

What is the soil condition down there? Is the soil compactable without gravel and still drainable?

By the way, I have never heard that you can do without the crushed stone sub-base under a slab on which a single-family house will stand. But you never stop learning.

Sure, it's possible - we did it no differently. Natural sandy soil - blinding layer and then the slab.

By the way, I have never heard that one could do without the gravel sub-base under a slab on grade, where a single-family house will eventually stand.

In principle, structural engineers decide, based on the results of the soil report, which foundation is carried out.

Lean concrete is more precise regarding the cover dimensions during the later concreting process. A blinding layer, as executed in Sebastian’s construction project, is somewhat more difficult to handle. Both ways are possible.

Of course, I don’t know any construction project where the gravel shifted. And if it did – the civil engineer would probably have completed his first and also last job.

Rhineland regards

My clean layer was made of lean concrete - that was the first thing I insisted on

That strongly depends on the foundation and the soil conditions. For us, strip foundations were used down to a depth of 1.30m, a blinding layer made of lean concrete, and on top of that gravel as a capillary break layer.