Waterproofing the foundations of a house

1. Why is waterproofing necessary?

What needs to be waterproofed? Balconies, terraces, flat roofs, and the joins between the structure, the ground and the foundation slab – these are all parts of the building that must be protected from water ingress using a continuous layer of polyurethane or bituminous waterproofing. Waterproofing also needs applying when repairing damage caused by hail or overheating, which leads to materials stretching or cracking.

2. Waterproofing materials

There is a whole array of new waterproofing materials available today. The most common are polyurethane and bituminous strips, the edges of which are glued or flame welded together to form a continuous layer. Narrower tape can be welded over the joins to give even greater protection. An easier method is self-adhesive sheets, which are applied direct to the structure. The advantages of polyurethane foil membranes are that, in addition to being 100% waterproof, they are resistant to all weather conditions, UV radiation, temperature fluctuations, and mechanical damage.

Bituminous coatings such as Fragmat or Ibitol are composite materials used in the waterproofing process. These mixtures are applied directly to the structure before the bituminous strips are laid. This can be by using the hot-applied method around the foundations, by placing the self-adhesive strips with grouting, or by gluing waterproofing panels.

3. Waterproofing the basement from the inside

Standard waterproofing methods, which have long been used, involve applying waterproofing on the inside of the building, i.e. onto the base slab. The plinth is lined with rigid foam insulation, in accordance with SIST EN 13163 of the European Directive on Construction Products. XPS is used for waterproofing, but also serves as thermal insulation. (1) The foundations and the outside of the wall of the building should be coated with Ibitol before the installation of waterproofing. (2) Bituminous strips are then flame-welded to the plinth area, from the height of the basement slab up to about 30 cm, and over the foundation slab. (3) If the building is exposed to water under pressure, two or three layers of bituminous strips are applied. The number of layers of waterproofing depends on the depth of the structure.

4. How to properly install waterproofing

More modern waterproofing techniques involve the concrete slab being waterproofed from the outside, where the building and the ground meet. The procedure is carried out as follows: (1) In order to protect against the pooling and penetration of water, which after a long while can cause the foundations to swell and lift the whole building up, rigid foam boards, 5 to 8 cm thick, with shiplap edges on all sides, are laid beneath the foundation slab. They are placed over the prepared subbase. (2) Self-adhesive bituminous strips are glued over the foam boards, with the overlaps welded to ensure water cannot penetrate. (3) Polystyrene boards, 2x10 cm or 20 cm, are laid over the bituminous membrane. (4) The outside of the wall is coated with Ibitol, over which bituminous strips are stuck with the overlaps welded, and finally (5) another layer of polystyrene is applied. (6) If there is water pressure or hydrostatic pressure, a dimpled membrane is also laid.

5. Waterproofing a flat roof

Due to its direct exposure to the elements, a flat roof must be waterproofed to ensure its longevity. There are various types of flat roofs, on concrete or other types of structures, but what they all have in common is that they must have a minimum slope of 2% so precipitation can run off as no waterproofing can protect against standing water. Generally speaking, (1) the roof structure must first be coated with Ibitol and then (2) bituminous strips are placed over it as a vapor membrane if there isnt already one on the inside. Depending on the complexity of the building, (3) 10 to 25 cm thick polystyrene insulation boards faced with fleece are then laid. (4) For the final layer, two layers of bituminous strips are applied; the first layer is only welded at certain points, while the second is welded completely, along its entire length and width.

6. Dimpled membranes

6.1. What is a dimpled membrane for?

A dimpled membrane is made of high-density polyethylene. It is pressure resistant and waterproof. The dimples create a drainage space that protects the surface below. This membrane is used for waterproofing foundations, retaining structures, and the joins between buildings and the ground.

7. Izotekt V4

7.1. What is Izotekt?

Izotekt or Izotekt V4 is the commercial name for a bitumen waterproofing membrane produced by Fragmat, although the name is increasingly being used to refer to bitumen waterproofing in general. Izotekt is ideal to replace fibreglass mesh, which is usually coated with bituminous mixtures and serves to enhance the strength and durability of the waterproofing membrane. It is mostly used for waterproofing residential buildings and is applied in one or two layers. As with bitumen, it is applied using the welding method and strips must overlap.