How do you prevent cracks in the screed on a precast concrete slab floor in the bathroom?

In precast concrete slab floors, a prestressed reinforcement is applied at the bottom. That reinforcement is placed under tension. As a result, it’s slightly bent in the factory and then settles into a neutral, horizontal position due to load and the passage of time.

This type of floor is full of hollow channels which reduce the weight of the floor. The floor slabs are connected to each other by pouring a funnel-shaped connection with a fine (spramix) concrete. If this isn’t done properly, rectilinear cracks can form on the seams of the floor elements, which also continue into the screed.

For both structural and watertightness reasons, Forbo Eurocol recommends finishing precast concrete slab floors with a concrete topping. In practice, this type of floor isn’t always equipped with this. Thanks to this concrete topping, all recesses are properly filled, underlying thickness differences between the precast concrete slabs are prevented and almost all pipes on and in the floor are concealed. Any tensions in the floor are absorbed by the topping so that no damage or leaks occur. It also creates a tight wall-floor connection.

Afterwards, a sand-cement screed can be lubricated with the additive 055 Additive to achieve watertightness. The mixing ratio for this is 3 litres of 055 Additive to 50 kg cement. After sufficient drying, the 063 Eurotape/685 Eurocoat system can be applied without any cracks to the tight wall-floor connection. Once this has been done, the floor tiles can be fully glued with a cement-bound powder adhesive, for example 705 Special Adhesive. Once the tiling has dried sufficiently, the tiles can be grouted with 706 Euro Grout Special WT. With this method, the risk of shrinkage cracks in the sand-cement screed – and thus in the tiling – is reduced to a minimum. In short, the result is better quality, which prevents many complaints!’