Although the temperature of the warmth carrier is not high in the system of floor heating, internal stresses can appear in layer of the concrete screed. Expansion joints are designed to prevent the formation of crack in the concrete screed and reduce stress to a minimum, limiting their distribution to the construction of the finished floor and walls. Significant stresses can appear on incorrectly done temperature joints in large areas or areas of complex shape, and this leads to chipping tiles or lifting of parquet flooring.
The expansion joints should be arranged like this:
- on the perimeter, along the walls;
- for limiting areas;
- with area of the screed more than 40 m² or with respect to sides 2:1with a maximum length of one of the sides being 8 metres;
- at the connection nodes of connections of differing building constructions, for example, a node of connection of a flight of stairs to its landing;
- passes through openings, for example of doors;
- areas with complicated shapes, for example, U-, L- shaped areas
In rooms with high temperature floors (swimming pools or rooms with floor coverings with high resistance to thermal conductivity, for example, carpeting, wood, etc.) expansion joints should be a little more numerous. The risk of cracking in the concrete screed in these structures increases.
Expansion joints (see Figure 109) are made with the help of compensation tape, made of polyethylene foam or other soft material. To make joints inside rooms, wooden (plywood, Plexiglas etc. ) slats can be used, which are removed after pouring the concrete screed and the crack is filled with elastic paste — hermetic. Materials for making temperature joints are also put in place before the installation of floor heating. The pipes should be arranged in such a way to minimize the quantity of passes through the expansion joint. In the places where a pass is unavoidable, the pipe (a 40-cm section) should be installed in a protective tube or in a steel sleeve with a length not less than one metre. This will prevent hard contact between the heating pipe and the screed while passing the temperature joint and also will exclude the possibility of action of shear forces on the pipes and creating cracks in the floor screed.