It happens time and again that complaints are received about cracks in or the complete rupture of base joints. In most cases, this is caused by excessive tensile stress acting on the elastic sealant – the maximum allowed distortion is 20 – 25% for most sealants – or by shrinkage occurring in the screed.
Almost any screed undergoes some shrinkage. In most cases, jointing work is performed before the screed has dried fully. Gradually, the structure which was still relatively moist when completed, will dry to the extent possible in the given situation. As a result the previously higher edges will start sagging, which in itself is enough to subject a joint to considerable strain.
Additionally, in many cases, the dimensions of joints are too narrow. Hence, the necessary back-filling material can be placed only with difficulty or not at all. For this reason, the joint can be spray-filled only as a triangular chamfer. This in itself entails a high risk of cracking, as movement in the zone of the joint is concentrated almost exclusively in the apex of the triangle.
A wider joint spray-filled in the shape of a rectangle and including back-filling is capable of absorbing movement in the zone of the joint without problems and with almost even distribution.
It should also be noted that the unavoidable distortions of floating structures generally exceed the elasticity of the joint filler compounds. These elastic sealing compounds require maintenance.