Fluctuations in temperature and moisture cause movement in the subfloor and result in cracks transferring to tile and stone coverings—or worse, cause a loss of bond between the covering and the substrate which can result in overall damage to the surface covering. For this reason, industry standards state that all tile and stone installations should include the use of movement joints.
In many circumstances, movement joints are overlooked or left to the contractor; however, a lack of movement joints can be a contributing factor to many different types of failure. Furthermore, if movement joints are not included in the specification, liability for any resulting problems (even if the problem doesn’t directly relate to a lack of movement joints) could fall to the architect, as it’s their responsibility to specify the type of joint and location of them.
The question, however, is how do you provide the movement joints necessary to ensure a durable installation and what movement joints should you use?
Movement joints have to go through screed to the covering, with consideration to intermediate surface joints and therefore need to be designed into the specification. Understanding the types of movement that can occur—namely drying shrinkage, differential movement, deflection movement, structural movement, moisture movement and thermal movement—will help when deciding which type of movement joint will best counteract the resulting stresses.
In floors, there are two basic types of movement joints: structural and non-structural. Both types will be subject to different movement patterns—for example, whether movement will occur from the covering through to the floor slab or just in the covering assembly, and this will affect the type of joint needed to prevent damage.
Pre-formed joints can accommodate roughly 15-20% of their movement zone. Schlüter®-DILEX movement joints offer complete protection and are available to specifiers in a wide selection of materials, colours, and movement capability.
Schlüter-Systems Ltd has NBS Clauses and BIM Objects available on NBS Plus, National BIM Library and at www.schluterspecifier.co.uk