When designing stone structures, account has to be taken of deformations caused by temperature changes and shrinkage. In the internal leaves of cavity walls and internal walls this mainly involves shrinkage. Stresses will occur as these deformations are generally impeded to a certain degree. If of sufficient magnitude, the tensile stresses could lead to cracks. The design of the movement joints must be aimed at preventing these cracks as far as possible. Movement joints can also be necessary from a structural viewpoint!
Two types of movement are distinguished, building physical movement and architectural movement. Movement joints that are required to prevent crack formation as a result of imposed deformations are known as building physical movement joints. Movement joints that are required from a structural viewpoint are known as architectural movement joints.
With walls we consider three situations:
Load-bearing walls Load-bearing walls connect to concrete floors at the top and the bottom. Concrete and masonry have different material properties and each wants to deform in its own manner. A wall made from calcium silicate will shrink somewhat, but this will be impeded by the floors. Because this deformation is impeded, stresses are created. Whether or not a wall cracks depends on various factors: •length / height relationship •thickness of the wall •nature of the impediment •presence of gaps •the magnitude of the impeded deformation
From a certain wall length movement joints will be required in order to prevent crack formation.
Non load-bearing walls The same factors as above are involved for non load-bearing walls. We distinguish two cases for non load-bearing walls. A non load-bearing wall on foundations is not impeded from moving at the top of the floor in comparison with a load-bearing wall. The maximum wall length without movement joints can therefore be greater than for a comparable load-bearing wall. For non load-bearing walls on a bending surface, (floor or steel girders for example) the structure will be subject to some bending. This means that the wall is not fully supported. The result of this is that other stresses can occur in the wall in addition to shrinkage stresses, which can lead to the earlier formation of cracks. Movement joints in the wall reduces these stresses. In this case we are concerned with an architectural movement joint. Here it can be assumed that, with non load-bearing walls without foundations, movement joints are required for two reasons: to reduce the shrinkage stresses and/or to prevent the stresses as a result of building on a bending surface.
Movement joints All load-bearing and non load-bearing internal walls should have movement joints included at specific distances to prevent the formation of cracks. For projects using modular blocks free and without obligation, movement joint advice can be requested from our Building Engineering department in Vuren. The movement joints in large format blocks are shown in the working wall drawings. Three types of movement joints are distinguished:
Dry movement joints Can be finished by the direct application of at least 150 mm wide self-adhesive glass-fibre tape, having a perforated fabric with a width of 50 mm in the middle (manufacturer MB Dilatape or equivalent). If the wall components on either side of the movement joint change in relation to each other then the movement joint should be levelled first using a skim plaster. Allow this skim plaster to harden before applying the self-adhesive glass-fibre tape. It is not possible to construct toothed movement joints in chamfered large format blocks. Cold movement joints in a wall with a plaster layer, over which a non-elastic paint layer is applied, can be finished with 2 x casing bead with 1 to 2 mm intermediate space with a sealant that remains elastic behind this.
Filled movement joints Can remain visible in the wall finish by not terminating the plaster layer on both sides in a so-called casing bead. It is necessary to keep the casing bead at least 3 mm apart from each other and to fill the opening airtight with a sealant that remains elastic and can be painted over.
Flexible joint Walls on bending surfaces should always be flexibly connected to walls on the non-bending surfaces using a flexible anchor or dilation anchor. In addition, connections between walls of materials other than calcium silicate should be using a flexible construction.
