Movement joints in tiled installations

The various components that form a tiled installation, i.e. background, adhesive, tiles etc. all have unique physical characteristics that affect their behaviour and cause them to expand and contract at different rates when subjected to things such as moisture, changes in temperature and loading. This differential movement causes movement stresses within the tiled installation which can lead to failures such as grout/tiles cracking and tiles loosening and debonding.
The provision of movement joints help to protect the tiled finish absorbing the movement stresses. Movement joints should extend through the tiling and adhesive bed and can be formed by using suitable sealants or pre-formed movement joint profiles. Sealants are generally suitable for use in wall tiling, around the perimeter of floors and may also be used to fill inter-mediate movement joints in floors which will only be subjected to light foot traffic where neither the edge of the tiles or sealant will be exposed to high levels of impact or abrasion.

CONSIDERATION
British Standard BS 5385, the code of practice for the design and installation of internal and external ceramic, mosaic and natural stone tiles, states that the building designer should assess the magnitude of any stresses and decide where movement joints should be located. Consideration should be given to the construction materials, bedding systems, anticipated temperature and humidity conditions, areas concerned and the setting out of the tiling.
Where underfloor heating is to be used, the pipes or cables should be located to ensure the system is contained within the pattern of expansion joints. When wall tiling is planned onto mature and stable backgrounds such as existing render or plaster, the non-structural movement joints in the tiling might need to extend only through the tiling and its bed. It is essential to ascertain that the background or base is able to support the additional weight of tiling before the type of movement joint is determined. It should be noted that the use of large format tiles may result in tiles being cut to accommodate movement joints in the tiled finish.

INTERNAL WALLS
In accordance with British Standard BS5385-1:2009, movement joints should be provided:
a. Over existing and/or structural movement joints
b. Where tiling abuts other materials
c. Where tiling is continuous across junctions of different background materials.
d. In large tiled areas, at internal vertical corners and at 3m to 4.5m centres horizontally and vertically (where large degrees of thermal movement or vibration are expected, the frequency of movement joints should be increased to accommodate the movement)
e. Where stresses are likely to be concentrated, for example at changes of alignment.
f. Movement joints should be of a suitable width to permit the sealant to accommodate the expected movement (typically 6mm)

EXTERNAL WALLS
In accordance with British Standard BS5385-2:2015, movement joints should be provided:
a. Over existing and/or structural movement joints
b. Where tiling abuts other materials
c. Junctions between different background materials, where tiling is continuous across them
d. Storey heights horizontally and approximately 3m to 4.5m apart vertically; ideally they should be located over movement joints in the structural background and at structural material changes; for example, horizontal joint at top and bottom of floor slab, vertical joint at internal corners and at junctions with columns
e. External building corners, vertically between 0.25m an 1m from the corner and symmetrically wherever possible
f. At internal corners
g. Movement joints should be of a suitable width to permit the sealant to accommodate the expected movement (typically 6mm)

FLOORS—INCLUDING HEATED FLOORS
In accordance with British Standard BS5385-3:2014, movement joints should be provided:
a. Over existing and/or structural movement joints
b. Perimeter movement joints should be inserted at door thresholds and where the tiling abuts restraining surfaces such as perimeter walls, columns, curbs, steps and plant fixed to the base
c. In larger internal floor areas, intermediate movement joints should be provided to form bays of size not greater than 10m x 10m
d. In larger external floor areas, intermediate movement joints should be provided to form bays of size less than 10m x 10m
e. On suspended floors, stress relieving joints should be inserted where flexing is likely to occur, e.g. over supporting walls or beams.
f. Internal floors, which might be subjected to significant thermal changes, i.e. direct sunlight in atria, or underfloor heating etc, the floor area should be divided up by intermediate movement joints provided at 5m intervals in both horizontal directions to provide 25m2 bays. N.B. These bay sizes may be increased to 40m2 when Norcros Permalayer anti-fracture matting is used.

HEATED ANHYDRITE/CALCIUM SULPHATE SCREEDS
In heated calcium sulphate floor screeds, movement joints should be detailed:
• Over structural joints in the underlying construction. These movement joints through the screed and tile bed should coincide with and be designed to accommodate the same movement of the underlying structural joints.
• at perimeters of floors where the screed abuts walls and up stands and at door thresholds.
• as a movement joint through both the screed and tile bed dividing the tiling into areas not greater than 40m2, or in accordance with the screed suppliers or screed manufacturers instructions. The areas bounded by movement joints should be square to rectangular with the width to length ratio not exceeding 5 to 8.
• as movement joints at significant changes of width of the screed surface and in doorways (ground plan length over 5m) with several rooms arranged one after another within a floor plan.
• as a boundary joint isolating areas of screed with separately controlled heating circuits.
• at doorway thresholds between separate areas of use.
• at junctions between heated and unheated sections of the screed.

The width and spacing of movement joints should be sufficient to accommodate anticipated thermal movement of the screed between the maximum operating temperature and expected lowest temperature of the screed. The coefficient of thermal expansion of the pumped calcium sulphate screed should be taken to be 0.012mm/m2/oC.
If the detail provided by the screed manufacturer states that there might be changes in length during installation (expansion), these must also be taken into account when calculating the necessary width of movement joints.
Note that, though pumped calcium sulphate based screeds can be laid in large areas without joints, where joints are required in heated screed they will have to be formed during the application of the calcium sulphate screed. This will require the use of formwork or the use of proprietary pre-formed movement joint profiles designed for this purpose.

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Technical Support

For technical information about Norcros Adhesive products please call: 01782 524140

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