Managing movement for installation success
By Carl Stokes Head of marketing Schlüter-Systems LTD.
MOVEMENT joints play a vital role in a tile or stone installation; each individual installation will feature different materials and the exact dynamics of their interaction are far from certain.
One thing is for sure, however: in almost every case the substrate will move differently to the covering material, and with so many variables at play, neglecting to consider movement joints at the design stage is a risk.
Specifiers often voice concerns about the appearance of movement joints, deeming them to have a negative effect on the aesthetics of an installation. But if specified correctly, movement joints should work with rather than against the overall installation and go largely unnoticed.
The primary focus of a movement joint is obvious from the name, but the modern market offers various material and colour finishes to suit an installation, making them more inconspicuous by the day.
The movement, expansion, and control joint profiles of the Schlüter-DILEX series offer a maintenance-free and functional solution, controlling movement in the substrate and surface covering when installed inline with the recommendations of British Standards (BSI) BS 5385.
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:
- Thermal movement – changes in the shape, area and/or volume of materials due to temperature changes and fluctuations
- Moisture movement – moisture enters buildings through porous surfaces as liquid or as vapour, causing movement
- Drying shrinkage – contraction and shrinking 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.
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 you’ll 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 joint to specify:
Schlüter-DILEX-BWA provides a flexible connection between tile or stone surfaces and existing coverings or structures, such as 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:
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 10m 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’ll 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 about 1:1.5.
Generally, the tile or stone field should be kept as square as possible and where underfloor heating is present, the field shouldn’t exceed 40sq m.
However, most floors tend to be rectangular rather than square; rectangular shapes aren’t 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 aren’t normally required, unless conditions (eg temperature changes) generate stresses which are likely to become extreme.
Uncoupling membranes and movement joints: The perfect partnership
For comprehensive handling of material expansion and contraction, movement joints should be used in conjunction with an uncoupling membrane. If tile or stone is bonded directly to the building structure, there is no ‘give’ between the two parts of the assembly; the differing rates of expansion in the materials can result in the development of tension and cracking of the surface covering. An uncoupling membrane is installed as an intervening layer between the tile and substrate to prevent this from happening.
Schlüter-DITRA 25, the unsurpassed uncoupling membrane of over 30 years’ standing, is the perfect partner to Schlüter-DILEX movement joints.
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 the adhesive doesn’t 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 and mechanical lock, 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.
SOLUTION IN ACTION
Project Intu Victoria Centre, Nottingham
The Intu Victoria Centre is a high-profile East Midlands’ shopping destination in the centre of Nottingham. Originally constructed between 1967-1972, it underwent a refurbishment and extension in 2014-15 that included external alterations to the clock tower entrance, change of use of existing floorspace to provide new food and drink units, new lighting, new flooring and bathroom upgrades.
When it came to uncoupling and movement joint provision for the upgrading of Nottingham’s main shopping centre, Schlüter-Systems provided a solution that is helping the new floorcovering to withstand the footfall of over 20 million visitors a year.
The project utilised 5,000sq m of Schlüter-DITRA 25 uncoupling membrane and 1,250 Schlüter-DILEX-EKSN 12.5mm stainless-steel movement joints with grey inserts, to provide protection for the vast expanses of 800x400x10mm porcelain tiles installed within the project.
The uncoupling membrane was used on the ground level, where the tiles were being overlaid onto an old terrazzo floor, and the movement joints were used throughout the 10,000sq m area.
The shopping centre remained open throughout the project, which is testament to the ease with which the product solutions were installed; installers worked through the night, laying 100-150sq m of tiling per session using rapid-set adhesive.
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 45-60 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.
NBS Clauses and BIM Objects for Schlüter-Systems are available on NBS Plus, National BIM Library and at www.schluter.co.uk.