Plinth waterproofing

Plinth and foundation wall damp- and waterproofing
Structures coming against ground should be waterproofed in places where hydrostatic pressure can develop against the surface of the structure. Situations where there is hydrostatic pressure may be incidental, typically occurring with heavy rainfall or meltwater making the ground waterlogged in spring.

Damp-proofing is sufficient for structures subject to normal ground damp and where hydrostatic pressure cannot occur. The capillarity of soils around structures should always be as low as possible. The slope of the topsoil away from the building should be sufficient so that hydrostatic pressure cannot occur around buildings.

Waterproofing should always be made with elastomer bitumen membranes. FOUNDATION WALL AND RADON BARRIER MEMBRANE is a torching felt developed for this purpose. Alternatively it is possible to use other TL2 class elastomer bitumen membranes. To ensure adhesion, the foundation wall should be primed with bitumen solution K-80.
Damp-proofing may be done with brush-applied bitumen solutions K-80 (primer) and K-70, two layers usually being applied over the primer. The coatings should be surface dry prior to applying the next coating.

Katepal Dimple Sheet is manufactured from weather resistant HDPE plastic. It is a black studded board, which is installed against the foundation wall surface with the studs facing the wall. The upper edge is always sealed with a cover profile, which will then be overlapped by the facing of the plinth. The footing and the lower part of the foundations should be protected with foundation wall membrane before installing the dimple sheets. The upper edge of the foundation wall membrane should be at least 300 mm above the lower edge of the dimple sheets. If there is a possibility that the level of trapped water in the ground may rise higher, the upper edge of the membrane must be correspondingly higher.

In many instances, as is nearly always the case with shallow foundations, the dimple sheets may be replaced by the foundation wall membrane all the way to ground level, which eliminates the need to use two separate products and overlapping installation.

DPC (Damp Proof Course) strips are used between the concrete structure (Leca lightweight concrete blocks etc.) and timber structures to prevent capillary movement of moisture into the timber. The most common case is between the foundation and the cill plate of a framed timber wall. Similar usage is found between concrete floors and framed timber walls and partitions. Normally the DPC over the foundation is manufactured from bitumen felt by cutting it into suitable strips. Their thickness and surface coatings (mineral granules, sand, plastic/torching bitumen) vary. Common widths of DPC over the foundation are 100, 150 and 200 mm.

Self-adhesive DPC strips for foundations have adhesive bitumen on their lower surface under a plastic film. The top surface has a coating of mineral granules. The width is 330 mm. It may be used like other types of DPC strip for foundations, but thanks to its easy adhesion, it is easy to install over the plinth below exterior brick or blockwork and to bend the other edge up against the back of the wind barrier so that water that may have entered the structure drains towards the open header joints of the lowest course and out of the structure. In this case a separate DPC strip should be installed under a framed timber wall or the inner leaf of a brick wall.

If a radon membrane is installed over the foundations, a separate DPC strip below the framed timber structure is not necessary. In a framed timber building with outer brickwork facing, a self-adhesive DPC strip is needed to protect the timber frame from water dripping to the bottom of the cavity.