The term “expansion joint” is used in the tiling industry. It defines a narrow gap, deliberately created through a tile installation, which allows a slight movement of the installation itself to occur after its completion without sustaining any damage.
The term can be interchanged readily with “movement joint” without losing any meaning. The joints themselves are either filled with a specific, highly elastic sealant, or left empty and shielded with a protective cover.
A PVC expansion joint which can absorb small movements in a tiled floor.
Mitigating Against Movement
With regards to construction, the designers (we’ll refer to all professional architects, surveyors, specifiers, and engineers as “designers” from now on) are very aware that the majority of the components of a completed project are likely to move, if only fractionally, at some stage. It is crucial, therefore, to allow for this movement during the design stages, so that all parts of the building are free from undue stress. Thus it is extremely unlikely that there will be any related structural problems in the future.
This movement allowance extends to the installation of ceramic, stone, and porcelain tiles. While these are generally not loadbearing or structural components, they require the same attention as other aspects of the build, because they're usually cemented fast to structural substrates. Indeed, one of the most important aspects of fitting these products is allowing for their likely movement.
There are many requirements and standards laid down in UK building regulations (BS 5385) broadly dealing with the issue of expansion. These cover every aspect of the construction, such as walls, roofs, and foundations. These standards provide reliable recommendations concerning the location and design of the joints. Designers are expected to be fully compliant with them – expansion joints are not optional. They will have at their disposal, for example, lists of expansion rates of the majority of building materials – certainly the most common ones.
It's up to these designers, and not the builders, to perform the necessary calculations which will evaluate the extent of the expected movement, over either a long or short period of time, of all the materials used in the project.
Particularly on large commissions, the designers, having performed these required calculations, have the responsibility to outline in the plans the requirements, locations, and details of any movement joints required, before handing over to the construction team. They should be clear and unambiguous. Included in this task are the details concerning tiles and stone. They’re also responsible for ensuring that instructions have been followed, through regular inspection of the project.
A rubber filled metal expansion joint, which will absorb movements in a tiled floor.
What Causes Movement of Tiles?
There are a number of conditions under which there can be movement in wall and floor tiles. It should be noted that in all circumstances where these types of movements might be expected, the use of flexible adhesives and grouts should be specified.
Physical Dynamic Movement of the Building Itself
Any settlement of a building, or vibration, or deflection at any stage can transfer stress through the tile installation, leading to movement. For extreme cases, large “seismic” movement gaps are created. The magnitude of the forces involved is such that it will make no difference whether the moving surface is tiled with standard ceramic or a tough porcelain - if there is no space for the tiles to move into, some of them will be destroyed as the stress is transferred through the installation
Changes in the ambient temperature of the environment in which the tiles have been installed can lead to failure of the bond between the tiles and the substrate. Even during the course of a regular day, there'll be significant variation in temperatures experienced by the tiles. Add to that the increasing trend towards underfloor heating systems, which provide quite a sudden surge in the energy through floor tiles, and it becomes apparent there'll be thermal expansion of the area.
In fact, in situations where tiles fitted indoors are surrounded by large glass windows, exposure to hours of hot sunshine will have the same effect. This becomes more obvious with outdoor installations where surface temperatures can easily reach 50C in direct sunlight, but could plummet in a matter of seconds in the event of a sudden rain shower.
Bear in mind that the thermal properties of the tiles, the adhesive, and the substrate will all be different, and they will all expand and contract at different rates.
Shrinkage of the Substrate
One of the most common causes of problems concerns the shrinkage of a freshly poured concrete screed on which the ceramic or porcelain tiles are laid. As the substrate cures, it loses a percentage of its water content, and therefore volume, to the atmosphere. The resultant shrinkage can cause catastrophic failure of the tiles, usually in the form of cracks as they are rent asunder by these massive forces.
In small areas an expansion gap may not be required. However, it’s still crucial that the tiling is done either after the moisture level of the screed has reduced to the required level, or in conjunction with decoupling systems, which is a thin flexible “mat” laid between the concrete base and the tile adhesive.
In large areas, expansion joints will be necessary for the concrete itself, for all the same reasons as are needed for wall and floor tiles.
Expansion of the Substrate due to Ingress of Moisture
Like shrinkage, any change of moisture content will result in a change of shape and size, ultimately leading to movement, with similar consequences.
Intrusion of other building substances
This refers mainly to areas where the tiles come into close proximity to other materials in the building, such as walls, pillars, skirting boards, architraves, window frames, step risers, baths, shower trays etc. If these other elements experience movement in a situation where they directly abut the tiles, it’s possible that the increased pressure will cause damage to the tile installation. A safe gap, therefore, should always be left around the perimeter of the tiled area.
An aluminium expansion joint where wall and floor meet, designed to accommodate seismic movements and deformation of construction materials.
Damage and Failure
The damage to a tiled floor or wall that has been caused by any of these complications can manifest itself in a number of ways:
- Grout can become cracked or loose, and come out of the tile joints.
- Tiles can crack under the enormous forces encountered when they’re cemented to a section of expanding or contracting substrate.
- Tiles will usually crack if the substrate itself cracks, presenting a more serious problem.
- Tiles can become loose as the bond fails. If tiles are being forced towards each other they can often “rise up” in tandem slightly from the floor, like a tent. To get an idea of how little movement it takes to create this problem, place a plastic ruler on a flat surface and push each end towards the other so that the ruler bends upwards. At just 2 mm shorter, the ruler will have buckled upwards approximately 3 cm at its highest point.
Note that tiles that are bonded particularly well are more likely to crack to relieve the pressure, as opposed to de-bonding from the substrate.
Types of Joints Used in Construction
A Cold Joint is the accommodation gap allowed between two separate pours of concrete slabs. Where possible, the tiling joint should be located directly in line with this. Otherwise, it should be located as close as possible, and a decoupling mat should be used.
A Construction Joint – Like cold joints, which separate two sections of substrate entirely, a construction joint is specified where two pours of substrate will meet, but the intention is not to treat them as separate units. Due to time constraints, it may not be feasible on any given day to continue installing the substrate. However, the intention is to continue the substrate as if it were all one unit, so either mechanical fixings are affixed or changes of angle in the interfacing plane are created.
An Isolation Joint is created at the meeting of two separate construction elements, such as a wall and a floor substrate, two different walls, or a floor and a pillar.
A Structural Joint separates different sections of the entire building, allowing for independent motion.
Control Joints are groove sawn into the substrate, usually concrete, to approximately 1/3 of the depth of the substrate itself. The intention is that if any future cracking occurs in the substrate, it will happen at this weakened point, and not randomly.
In the above situations the designers will ensure, where possible, that these types of joints will be carried through the substrates, adhesives, and ceramic or porcelain tiles, creating a full clean joint through that section of the building.
Locating Tile Expansion Joints
The designers, when calculating the appropriate location for the joints, take into consideration a number of factors:
- the co-efficient of expansion of the tiles and substrates, the figure for which should be available from the manufacturers and general architectural references,
- the maximum expected range of temperatures that the installation will experience,
- the distance between the joints, which will have a lot of determining factors and may be dependent more on the overall structure of the building than just the tiled area itself.
As specified in BS 5385, the size of any one area of tiles should not exceed 10 metres in any one direction. However, in reality, and depending on the particular situation, somewhere around 8 metres is more appropriate for floors, and every 4 metres on walls. On suspended floors, this can often reduce to 5 metres. Outdoors, the joints should be more frequent again.
It should be noted that where there is an expansion joint in the substrate, the joint in the ceramic or porcelain tiles should correspond exactly in location, and be no narrower in width. This ensures that freedom of movement in either material will be in harmony with the other.
In every instance, movement gaps should be left around the perimeter of the installation (6mm is recommended), as well as in the circumstances mentioned above where the tiles meet a different building component. Joints are often required where there is continuous tiling over two different substrates.
What Are Joints Filled With?
While a “movement joint” is merely an empty space into which building components can expand and contract, in practice these gaps are occupied by specialised strips fabricated from one of any number of different materials. In turn, the strips are filled with flexible sealants, silicones or foams, or a combination of them, or other appropriate substances, in particular for large deep construction joints. For wall and floor tiles, the joints are usually filled with a flexible rubber.
These expansion joints prevent dirt and grit filling the space, as well as providing a more aesthetically suitable solution. The wider ones will usually incorporate a cover slip into their design.
Different kinds of environments demand different types of joints:
- In residential projects, nothing more than a PVC joint is required. This type will also be applicable in areas of light traffic, such as offices or around swimming pools.
- Aluminium models would be used in light commercial areas, such as showrooms or schools.
- For heavy commercial or industrial areas, where there may be ride-on floor cleaning equipment, pallet trucks, shopping trolleys etc., stainless steel is more applicable, as is brass.
An aluminium expansion joint for areas of heavy traffic. The clever ball and socket joint supports multi-directional movement, including up-and-down.
Nobody would argue that an expansion joint running across a floor or down a wall is in any way attractive. Aside from all the technical and engineering aspects, therefore, the designer also has to consider what the final appearance of the construction will be.
The joint strips come in an array of colours, and ideally they are matched as best as possible to the colour of the grout.
Since the tile joint is visible, many manufactures offer silicone sealants which match the colour of the grout. Where it’s possible to use a sealant instead of a strip, it can be difficult at first glance to distinguish between the expansion joint and the other grout lines.
To Wrap Up
All buildings move to a certain degree, and therefore it’s vital to allow for this movement using expansion joints. There are several reasons why this motion occurs, all of which need to be taken into consideration by designers.
Expansion joints for wall and floor tiles should ideally be located directly over the building’s own expansion joints. In large areas, many factors will determine how often a joint will be required. Each situation is different and needs to be assessed on its own merits.
Images courtesy of Emac, a leading manufacturer of trims and expansion joints.