Managing movement for installation success
By Carl Stokes, Head of Marketing, Schlüter-Systems Ltd.
Schlüter®-DILEX and Schlüter®-DITRA 25: The perfect partnership.
For comprehensive handling of material expansion and contraction, movement joints should be used in conjunction with an uncoupling membrane. Schlüter®-DITRA 25, the unsurpassed uncoupling membrane of over 30 years’ standing, is the perfect partner to Schlüter®-DILEX.
Schlüter®-DITRA 25 is a patented polyethylene membrane with a grid structure of square cavities, each cut back in a dovetail configuration, and an anchoring fleece laminated to its underside. The tile adhesive mechanically locks into the cut-back indentations on the topside of the matting, eliminating the need for additional anchoring mesh. This mechanical lock means that the adhesive does not adhere to the mat, avoiding the formation of a direct bond and allowing for independent movement.
The geometry of Schlüter®-DITRA 25 allows for the absorption of lateral movement in each direction. Through its unique two-layer design, this uncoupling mat truly separates the substrate and tile or stone covering by creating essential free space between the layers, in which the matting can move safely.
Equipped with the knowledge that an uncoupling membrane and movement joints will successfully handle material movement within the substrate and surface covering, we turn to another couple of key questions:
What type of movement joint do I need to specify?
Where do I place movement joints?
What type of movement joint do I need to specify?
To answer this question, it helps to understand the types of movement that can occur. These generally fall into one of the following six categories:
Drying shrinkage: Contraction and shrinkage causing an increase in tensile stress
Differential movement: Different parts of the structure moving at different rates
Deflection movement: The degree of movement when a structural element is placed under a load
Structural movement: Occurs frequently within buildings and can include expansion and contraction of the structure materials due to subsidence, settlement or sway, etc.
Moisture movement: Moisture enters buildings through porous surfaces as liquid or as vapour, causing movement
Thermal movement: Changes in the shape, area and/or volume of materials due to temperature changes and fluctuations
Each of the above influences stress on the structure, leading to movement in the material surfaces and substrates. There are different types of movement joint to deal with different areas of a building project.
We’ll now drop down into each type of joint that you will encounter, briefly explaining each one and highlighting associated examples from the Schlüter®-DILEX range.
Connection joints are movement joints placed in the screed and the covering at construction elements such as window openings, door frames, shower trays and bath tubs.
Example connection joints to specify within the tile covering:
Schlüter®-DILEX-BWA provides a flexible connection between tile or stone surfaces and existing coverings or structures, such as door and window frames.
Schlüter®-DILEX-AS is a joining profile for creating flexible joints to fixtures such as shower trays, baths, door and window frames.
Perimeter joints are movement joints placed in the screed and the covering along walls and construction elements that penetrate the screed, such as columns. They reduce impact sound transmission and absorb the movements of the floor assembly.
Edge joints must not be rigidly closed, since this may lead to the formation of sound bridges and tensions in the covering construction.
Example perimeter joints to specify:
Schlüter®-DILEX-KSA is a connection profile with edge protection. The profile’s anchoring legs, made of aluminium or stainless steel, are connected to a replaceable movement zone made of soft PVC. The profile is used for creating transitions between coverings and fixed structures such as window frames.
Schlüter®-DILEX-HKS is a cove shaped, stainless steel profile with a maintenance-free movement zone for floor to wall connections in ceramic tile or natural stone coverings.
Intermediate joint profiles in screeds
Intermediate joints create a pattern of limited fields in large areas of screed and covering. They must be continued from the surface of the covering to the separating layer under the screed or to the covering of the insulation or waterproofing layer. In door transition areas, the screed should contain movement joints which are continued in the covering, to reduce stresses occurring at these locations and to prevent the transmission of impact sound. Movement joints in the substrate must not be closed or covered with flooring materials.
Example screed movement joints to specify:
Schlüter®-DILEX-DFP is a movement joint profile that is installed at door transition areas or used to divide screed areas.
Schlüter®-DILEX-EP is a movement joint profile for application in floating or bonded screeds. The side sections consist of rigid, recycled plastic connected at the top and bottom with soft, grey CPE movement zones.
Example intermediate joints to specify for the tile covering:
Schlüter®-DILEX-KS is a movement profile with edge protection consisting of lateral anchoring legs made of aluminium or stainless steel, which are connected to a replaceable movement zone made of soft rubber.
Schlüter®-DILEX-BWS is a movement joint profile with side sections of rigid, recycled plastic. The movement zone consists of soft CPE and creates the 5mm wide visual surface.
Structural joints (expansion joints) are joints required for static or engineering reasons, which divide a building in various movement segments. They run through all load bearing and non-load bearing parts of a building and must be continued in the screed construction and the floor covering at the identical location and in the specified width.
Example structural joint to specify:
Schlüter®-DILEX-BT is a structural expansion joint made of aluminium with lateral joint connections to a sliding telescopic centre section. This allows for absorption of three-dimensional movement.
Where do I place movement joints?
Movement joints must be installed in certain locations and positions to prevent cracking, tenting and debonding of the tile, stone or grout. In placing movement joints, the idea is to create tile or stone ‘fields’ large enough to absorb the anticipated movement between the substrate and the tile or stone covering.
Industry guidelines for unheated screeds suggest that the maximum tile or stone field should be no more than 10 metres in each direction, but in practice – depending on the individual applications – it tends to be more in the region of between five and eight metres.
British Standards (BSI) 5385 covers the requirements and methods for movement joint applications. BS 5385 states that the building designer should assess the magnitude of any stresses and decide where movement joints should be located, considering all relevant factors, including the type of flooring, bed and substrate.
A circle provides the best configuration for movement joints, because the forces from the centre are equal in each direction. However, in practice you will more likely be dealing with square and rectangular floors than circular ones, so these provide the best basis. In a square configuration, the ideal field size is where the ratio of the shortest to the longest distance from the centre of the force is approximately 1:1.5.
Generally, the tile or stone field should be kept as square as possible and where underfloor heating is present, the field should not exceed 40 sq. metres.
However, most floors tend to be rectangular rather than square; rectangular shapes are not usually the best configuration, as the ratio of the shortest to the longest distance exceeds 1:1.5.
On suspended floors, stress-relieving joints should be inserted where flexing is likely to occur; for instance, over supporting walls or beams . Movement joints must be carried through and situated directly over any joints in the substrate, and at any changes in the substrate; such as timber to screed, new to old screed, and heated to unheated.
In areas less than two metres wide, perimeter joints are not normally required, unless conditions (e.g. temperature changes) generate stresses which are likely to become extreme.
A decorative finish
Movement joints aren’t the only profile consideration that should be incorporated at the specification stage of a project. When careful consideration has been made to the sanitary-ware, taps, shower, lighting and tile or stone covering in a kitchen or bathroom, the right choice of profiles gives that extra finesse. A strong palette of designs and hundreds of options for finishes, textures, materials and colours are available with Schlüter®-PROFILES.
Edge profiles for floors: Schlüter®-SCHIENE, the original finishing threshold strip or diminishing profile, finishes tiled surfaces and protects the outer edges of ceramic and natural stone floor coverings. The threshold strips, or diminishing profiles, of the Schlüter®-RENO series create a smooth transition between adjoining floor coverings of different heights, protecting the exposed tile or stone edge.
Wall corners and edge profiles: The profiles of the series Schlüter®-JOLLY, Schlüter®-RONDEC and Schlüter®-QUADEC create a highly durable and decorative finishing for wall coverings and skirtings made of tile and natural stone. Designer accents can be created by using these profiles in conjunction with the decorative Schlüter®-DESIGNLINE and Schlüter®-QUADEC-FS border profiles. 2017 saw the introduction of Schlüter®-FINEC, a slim-line profile that provides near-invisible edge protection and is ideal for use with mosaics and thin porcelain tiles.
On-trend textures for wall profiles: Introduced in 2016, Schlüter®-TRENDLINE is a selection of textured finishes for wall profiles. There are a variety of on-trend textured colours available to complement tile or stone: from beiges and greys that provide a great match for concrete, right through to rustic-brown for wood and graphite metal finishes.
Initially available exclusively for the Schlüter®-JOLLY, -RONDEC and -QUADEC ranges, TRENDLINE’s reach expanded in 2017, with its ivory, dark grey and anthracite finishes now available for application onto the internal wall corner profile, Schlüter®-DILEX-AHK.
Decorative skirting profiles: Schlüter®-DESIGNBASE offers a selection of decorative skirting profiles to satisfy a number of requirements. These range from Schlüter®-DESIGNBASE-SL, for no-frills finishing, through to Schlüter®-DESIGNBASE-CQ, which allows cables to be hidden within it, and Schlüter®-DESIGNBASE-QD, which can be combined with Schlüter®-LIPROTEC LED strips to provide lit skirting and wall border detailing.
Stair nosing profiles: The edges of stairs are exposed to heavy mechanical stresses and represent a high risk for injuries. Because of their slip-resistant design and excellent visibility, Schlüter®-TREP profiles improve safety and offer DDA compliance and protection. They can also be combined with Schlüter®-LIPROTEC illuminated profiles to add decorative visuals for unique designs on stairs, steps and plinth edges.
Learn more about specifying movement joints
Host the CPD seminar ‘Specifying Solutions for Crack-Free Tile and Stone Coverings’ to gain knowledge and confidence in specifying appropriate movement joints and uncoupling membranes. In this 45 to 60 minute presentation, held at your offices, you’ll learn how to counteract stresses in the substrate, such as drying shrinkage, deflection and thermal movement, with the aim of preventing cracked tiles, stone and joints etc.
Schlüter-Systems have dedicated consultants on hand to help with any stage of your specification project. For more information, call 01530 813396, email firstname.lastname@example.org, or visit www.schluter.co.uk.
NBS Clauses and BIM Objects for Schlüter-Systems Ltd are available on NBS Plus, National BIM Library and at www.schluter.co.uk.