How do I insulate a strip foundation from below?

Question

While building a strip foundation (a concrete wall starting several feet below ground) I have to insulate it from moisture because otherwise moisture will get into the foundation and into the basement. Insulating the sides is relatively easy - once the wall is there I can glue some stuff like ruberoid onto the wall or paint it with resin.

What about the foundation wall bottom? I cannot paint the wall bottom or glue anything to the wall bottom before the wall is there and once the wall is there it's pressed hard onto the ground and I cannot do anything with its bottom. This is kind of chicken-and-egg problem.

How is moisture insulation done for the strip foundation bottom side?

Answer 1

I have doubts that you are expressing yourself clearly or if, so , that you grasp the concept that concrete does not mind water a bit (if you are just building a wall, not a foundation that encloses a buried space as normal for a building, where is the water going to go that causes you a problem, down in the ground?)

In any case, you can lay a sheet of plastic on the base before pouring concrete. But I seriously doubt you need to do that or any other waterproofing, if you are just putting in a foundation for a free-standing wall. If that's not what you are doing, have another try at explaining what you are doing, please (edit your question) since that appears to be what you are describing with "strip foundation"

If you are building a normal, space-enclosing foundation wall, you can also lay plastic or EDPM rubber under the entire floor area, but the main thing is to lay drainage pipe outside the foundation, slightly below the floor level to remove water from the foundation area - depending on films or coatings alone is prone to failure against high water pressure - removing the bulk of the water is the most effective method to prevent water in the basement.

Answer 2

Damp Proof Membrane

To prevent dampness getting through a ground bearing concrete floor should be protected by an impervious layer, usually a 1200 gauge (0.3mm) heavy duty polythene damp-proof membrane.

The DPM can be positioned either on the sand blinding or on the concrete slab. Joints in a Polythene DPM should be welted or taped and should overlap by at least 300mm. The DPM must be linked with the DPC in the walls, to ensure that the entire interior of the building is protected from moisture by a continuous, impervious barrier. The DPM will need to be dressed up around service entry points.

http://www.buildingregs4plans.co.uk/foundation_floor_wall_3d_detail.php