Movement Joints, Expansion Joints And Control Joint Profiles. - Tile Advice

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Movement Joints, Expansion Joints And Control Joint Profiles from Schlüter®

The movement joints, expansion joints and control joint profiles of our Schlüter-DILEX series offer maintenance free and functional solutions for all relevant movement joints in tile coverings. The range includes profile types for movement joints, expansion joints and control joints, as well as edge and transition movement and expansion joints. All profiles are installed at the same time as the tile covering. A wide variety of Schlüter-DILEX movement and expansion joint profiles in various material combinations are available in accordance with the expected mechanical or chemical stresses on the covering. For more information, or to find your nearest distributor, contact Schlüter-Systems Ltd on +44 (0) 1530 813396.

 

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An Introduction To Movement Joints

Ceramic and stone tiles can be subjected to a variety of strains and stresses caused by movement in the tiled surface, leading to tiles bulging, cracking or becoming detached from the substrate. Movement joints compensate for the movement of tiles which extends down through the tiles, the bed and screed layer below.
Without them the shear stress builds up between the tile and the screed, causing debonding, bulging and cracking. Therefore these stress-relieving joints are an essential part of any tiling installation, and should be incorporated at the design stage.
Movement joints create a tile field which moves independently from those around it, and should be included at set distances in floor and wall tiles, in accordance with recommendations from the British Standards Institution (BSI). BS 5385 says the maximum tile field should be no more than ten metres in each direction for floors - but in practice, depending on the individual application, it tends to be between five and eight metres for floors, and every three to four-point-five metres on walls.
Installing the appropriate movement joints in line with those recommendations, will prevent tiles from cracking, bulging and debonding. And by "appropriate," that means one which can do what is being asked of it.
There are different widths of pre-formed movement joints, and the correct width and material - brass, aluminium, stainless steel or PVC - must be specified to take thermal movement into account.
The amount of movement that can be absorbed - and therefore the degree of protection given by the joint - depends on the size of the profile and the compressible material used. Pre-formed surface joints will usually accommodate movement up to 20% of the movement zone width.
A 10mm joint will extend and compress by approximately 2mm. One of Schlüter's stress relieving movement joints, the Schlüter-DILEX-KS, has a movement zone of 11mm, will accommodate up to 2.5mm of tile movement. Because there are specific movement joints for specific types of application, most tiling failures are caused by using joints that aren't suitable for what is being demanded of them. There are many situations, each with their own technically engineered solution in the form of the correct joint.

Very often the problem can be caused by using the wrong joint - one that is not able to meet the requirements that are demanded of it.

Generally aluminium is ideal for commercial use; with brass and stainless steel needed for heavy duty commercial and industrial projects such as warehouses, production facilities and airports, and where the tiled surface is cleaned by a scrubbing machine, or where there are rolling loads such as pallet trucks and metal-rimmed trolleys. Stainless steel is also ideal in places like laboratories and food processing plants where chemicals are used. PVC can be used for residential and medium duty commercial applications including offices and swimming pools, and areas subject to light mechanical loading such as showrooms and car dealerships.
Many calls to Schlüter's technical support service refer to application problems, where no joint or the wrong joint has been used.
Other callers seek advice before the work is carried out - and we would say that it's in everyone's best interests to ensure that ceramic and stone tiles are installed with the correct movement joints.
Prevention is always better than the cure which is why Schlüter is always happy to advise on the requirements of individual projects, as well as delivering a variety of training courses on the use of movement joints.

 

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Why Are Movement Joints Needed?

Ceramic or stone covering can be compared to a sheet of glass, in that each is rigid by nature. Movement joints must be installed in certain areas and positions to prevent tiles or grout from cracking...and in some cases prevent the tiles from tenting and becoming debonded from the substrate.
A movement joint is the interruption of the surface to allow for movement. Common terms are:
· Movement joint
· Expansion joint
· Stress relieving joint

They are needed because all tiles expand and contract with temperature and moisture changes. In almost every case the substrate will move differently to the covering material. The larger the tile field, the more it will expand and contract, and be vulnerable to failure. In 95 per cent of today's tile installations they will be fixed using the thin-bed method. This means the tile is adhered directly to the substrate with an appropriate adhesive. Movement joints accommodate the differential stresses within each "field" of tiling, so they don't build up to a level which would cause shearing stresses at the bonded interface, protecting the tiles from cracking, tenting and debonding.

Stresses from drying shrinkage, deflection and moisture movement in the substrate, plus thermal and moisture changes affecting the flooring, can cause loss of adhesion, resulting in bulging or cracking of the floor. In particular, deflections in suspended floors can induce high compressive stresses in rigid floor tiling, and may be the principal cause of "hollowness" in those situations. The shear stress resulting in the substrate and ceramic or stone surface moving differently from each other is often too great for the adhesive to hold - shown in the top picture.
Therefore, stress-relieving joints are an essential part of any tiling installation, and should be incorporated at the design stage.
There are different widths of pre-formed movement joints, and the correct width and material - brass, aluminium, stainless steel or PVC - must be specified to take thermal movement into account.
The amount of movement that can be absorbed - and therefore the degree of protection given by the joint - depends on the size of the profile and the compressible material used. Pre-formed surface joints will usually accommodate movement up to 20% of the movement zone width. For example, one of the larger stress-relieving joints at 15mm wide, with a movement zone of 11mm, will accommodate up to 2.5mm of tile movement.
However, as the majority of tiled installations involve the thin-bed fixing method, cracks in the substrate will readily be transferred to the surface, causing the tiles to crack. Where irregular hairline cracks in the screed or timber board joints are present, its not practical or possible to position movement joints over those. In this situation the best way of preventing damage is to incorporate movement joints with an uncoupling system, such as a polyethylene membrane, to separate the covering from the substrate, in order to guarantee the long-lasting integrity of the installation.

 

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Where Should Movement Joints Be Fitted?

The theory is to create "tile fields" large enough to absorb differential movement between the substrate and the ceramic or stone covering -- movement joints must be installed in certain areas and positions to prevent tiles or grout from cracking...and in some cases prevent the tiles from tenting and becoming debonded from the substrate. But the exact positioning of movement joints is vital to them successfully protecting the installation. If they're installed in the wrong place they won't work.
Industry guidelines suggest that the maximum tile field should be no more than ten metres in each direction - but in practice, depending on the individual applications, it tends to be between five and eight metres.
British Standards (BSI) 5385 covers the requirements and methods for movement joint applications. Part 3: 1989-Section 3 - 19.1.1 states that the building designer should assess the magnitude of any stresses and decide where movement joints should be located, having regard to all relevant factors, including the type of flooring, bed and substrate.
While the floor areas to be tiled come in all shapes and sizes there is a general formula for working out where movement joints should be placed.
A circle provides the best configuration for movement joints, because the forces from the centre are equal in each direction. However, in practice, because hardly any floors are circular, it is best to look at square floors and rectangular floors. 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 (see figure 1) -- for example 5 x 7.5 metres. Generally, the tile "field" should be kept as square as possible, and where underfloor heating is present, the tile field should not exceed 40 square-metres.

However, most floors tend to be rectangular, rather than square, though. And rectangular shapes tend not to be the best configuration, as the ratio of the shortest to the longest distances exceeds 1:1.5. In the example shown in figure 2 the crack risk is at the centre of the area. If no movement joint has been installed, cracking of the tiled surface is highly likely. In large floors it is advisable to incorporate movement joints forming bays at no more than 30-metre intervals. Each bay is then sub-divided into smaller bays by stress relieving joints not greater than ten metres apart.
On suspended floors, stress-relieving joints should be inserted where flexing is likely to occur...for instance, over supporting walls or beams. And, as always, joints must be situated directly over any joints in the substrate, and at any changes in the substrate, such as timber to screed.
For areas less than two metres wide perimeter joints are not normally required, unless conditions generate stresses which are likely to become extreme, for example temperature changes.

 

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Sealants, Or Pre-Fabricated?

The normal installation methods are either field-applied sealant, or a pre-fabricated movement joint profile. And which is better depends very much on the application. While sealant-type methods are suitable for most applications - and indeed, is the only method in some - a straight analysis of the two methods does identify a weakness in the sealant-type joints.
Silicone Expansion Joint
No edge protection
Retains memory
Requires maintenance
Two-step installation
Pre-fabricated expansion joint profiles
Edge protection
High elasticity
Maintenance-free
One-step installation
Straight uniform joint
Prevents sound transmission
Long-lasting professional installation

Figure 1 shows where the differential movement between the floor and wall has resulted in a torn silicone sealant joint. This also shows what is meant by "retains memory," where the sealant used has stuck to the surface with which it has the better bond - either the wall or the floor.
This type of damage is particularly common where a floating floor has been used, such as a heated screed, or timber. The damage seen here needs expensive remedial action, with the removal and cleaning of the damaged areas followed by the re-application of the sealant, which may fail again.
The problem is more acute in areas with high hygiene requirements, such as hospitals, food preparation areas, and leisure facilities. And, of course, if waterproofing was reliant on the sealant joint, that, too would have failed.

But the performance of a pre-fabricated joint profile in the same situation, would be very different.

Figure 2 shows a two-part corner profile which provides a permanent flexible connection at the floor-to-wall transition. This type of profile features a tongue-and-groove connection of approximately 8mm, which absorbs large degrees of movement - whereas, if a sealant-type joint were used in the same application, the width of the joint would need to be between 20-25mm to absorb the same movement. In addition, the tile pocket integrated on the floor anchoring leg allows cut edges of tile to be tucked into the pocket to give a better aesthetic appearance to the finished installation.

 

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Stopping Unsightly Fungal Growth

Most tilers can probably recall seeing where a silicone sealant joint has become soiled with a fungus infestation. Many field-applied silicone sealant joints have additives included in the material to prevent such problems, and may keep the problem at bay for some time, but even with these additives, fungal growth on and within the silicone sealant always seems to get a hold eventually.
Not only is it unpleasant to look at, it may cause problems in areas with strict hygiene requirements, such as hospitals and food preparation areas - particularly industrial kitchens - along with washrooms and shower rooms etc.

A simple and effective solution is to install a pre-fabricated profile at the internal wall-to-floor junction. The requirements of each individual application will dictate which material is used. For example, Figure 2 shows a stainless-steel cove-shaped profile which provides an easily-cleaned corner, where limited movement is expected. Aluminium and PVC are also commonly used, depending on the degree of movement the joint has to protect against, and what chemicals it may come into contact with. So either metal or PVC pre-fabricated joints are going to be of benefit at tiled floor-to-wall transitions.
The use of pre-fabricated coved profiles has an added benefit in that "sit-on" or "sit-in" skirting tiles are not required. A skirting tile is probably the best looking solution; however these are expensive, and a movement joint still needs to be incorporated. The coved profiles give both an attractive coved shape and movement joint protection all in one.
Other benefits include being very economical due to their long life, there can be no tears or cracks in the movement joint, and, with PVC profiles:
· The chemical structure makes them resistant to ageing, and the materials cannot rot
· They are unaffected by oxygen or ozone
· Resistant to the majority of diluted and concentrated acids, lyes and hydrous salts
· Resistant to fungi and bacteria
· Difficult to ignite, and self-extinguishing in the event of fire.
And with metal profiles:
· Choosing the correct material type guarantees protection against anticipated chemical or mechanical stress
· Resistant to fungi and bacteria
· No special maintenance required.

 

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Movement Joints - The Right One For The Job (Part One)

We've all seen cases where a tiled surface - particularly in heavily-trafficked areas such as shopping centres and airports - has become damaged. The right movement joint will prevent that from happening.
Without the appropriate solutions being in place, shear stresses can cause the tiles to crack, split and delaminate, as shown in Figure 1. To protect the tiles, intermediate stress relief joints should be incorporated into the surface assembly.

However, it's not a case of "one-fits-all" -- a different type of joint will be required for different types of application, depending on whether it is heavy duty, light commercial, or domestic. For instance, in areas exposed to high traffic, such as shopping centres and airports, it is important to use a movement joint with metal edges to protect the edges of the joint itself, while preventing damage to the edge of the tiles (see figure 2).
However, for residential or light commercial applications, such as offices and car showrooms, PVC profiles will be suitable. But metal edged profiles should also be considered where the tiled floor surface is likely to be mechanically cleaned. The profiles are fixed at the same time as the tiles are installed, so the only additional work needed is to grout the anchoring legs into place.
To ensure that there is a joint which is suitable for every conceivable individual application there are many different systems on the market. Because of this, their special features will make a particular joint absolutely right for one application, but wrong for another. Tilers must select a joint which is capable of doing what is being asked of it.

 

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Movement Joints - The Right One For the Job (Part Two)

The reason there are so many different systems available, is to ensure there is a joint which is suitable for every conceivable individual application. Most tilers know movement joints must be installed in certain areas and positions to prevent tiles or grout from cracking, and in some cases, the tiles tenting and becoming debonded from the substrate. But certain features make a particular joint absolutely right for one application, and wrong for another.
Some joints which are designed and engineered specifically for residential, offices, or light commercial use just wouldn't be able to cope with the mechanical stresses of heavy duty applications such as airport terminals and railway stations, for instance. For those sort of uses, you would need a much stronger profile which is also capable of withstanding greater degrees of shear stresses.
Here, we look at a selection of movement joints covering a wide variety of different applications. Figure 1 features an aluminium profile with a central movement zone. When installed, the visible profile is 6mm wide, which corresponds to the width of the average grout joint. This type of profile is suitable for commercial and heavy duty applications.

Many joints come in a variety of metal anchoring legs, as shown in Figure 2 - either aluminium, brass or stainless steel -- connected to a replaceable rubber movement zone. It's this zone which actually absorbs the movement, and can be replaced in the future if it becomes worn or damaged, without having to remove either the tiles or the profile. Each material is suited to different types of applications - whether a heavy duty or lighter duty profile is required all depends on how strong the joint needs to be. And, of course, that depends on what is being asked of it...namely, it has to respond to the expected mechanical or chemical stresses that the tiled surface will be exposed to.
Aluminium is suitable for areas like shopping malls, supermarkets and offices. Brass can be used in the same areas, but is much more resistant to high mechanical loads such as vehicular traffic, or those found in production facilities and railway stations.
While stainless steel can also be used in all applications it is particularly suited in areas which may be exposed to chemicals - places like laboratories, chemical production facilities and leisure centres.

 

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And for areas where the stresses aren't expected to be as forceful, Figure 3 shows a one-part PVC profile, with a visible surface width of 10 mm. These PVC profiles can be safely used for tiled surfaces both indoors and out. They're ideal for residential or light commercial use in offices, retail stores, shopping areas which aren't exposed to metal wheeled traffic, and car showrooms.

And for coping with structural expansion...Figure 4 shows a structural expansion joint profile which can be made of aluminium or brass with lateral joint connections to a sliding telescopic centre section. This allows the absorption of three-dimensional movement.

 

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Movement Joints - Part of a Complete Systems Solution

Figure 1 shows a familiar sight of a cracked tile. While the installation of movement joints will normally prevent such cracking, a particular problem can result from the tiles bridging a board joint over a timber substrate. In some cases it is simply just not practicable to insert a movement joint over every joint in the floor, especially if the joint or crack is irregular.
Adhesives used to adhere tiles rely on a strong bond to keep the tile firmly fixed to the substrate. But this type of bonding can pose problems with the transmission of shear stresses to the surface covering, particularly where there are board joints in the substrate. A solution would be to remove the shear stresses between the substrate and tile using an uncoupling system.
The British Standards recommend isolating a rigid covering, such as ceramic tile or stone, from the substrate, which is dealt with in BS 5385 Part 3. This states that failures arising from variable stresses can be avoided by isolating the tile bed from the base by using a separating layer which prevents the two elements from adhering to each other, and thus allows each to move independently.

In order to explain how this isolation works we need to go back in time. The sketch in Figure 2 represents tile fixing methods before the introduction of thin-bed adhesives. The floor assembly with ceramic tiles could be compared to a sandwich consisting of a load-bearing substrate, a filler layer of sand, the setting mortar, and finally the tiles on top. The ceramic tile or stone surface covering was the strongest and dominating element compared to the mortar and fill layer. But the stresses, deformations and cracks within the substrate could not be transferred to the surface covering, and floor assemblies like these have lasted for many centuries without damage occurring.

In order to isolate the covering from the substrate with modern thin-bed methods, if we take this type of tiled application and apply state-of-the-art technology, an uncoupling system can be produced that works in a similar way. A membrane type uncoupling system, such as Schlüter-DITRA, which is illustrated in Figure 3, prevents damage to the ceramic or stone surface, even when tiles bridge a board joint as in Figure 1. Schlüter-DITRA has a uniform three-millimetre-deep grid structure of square cavities cut back in a dovetail configuration. An anchoring fleece is laminated to the underside, and the mat is installed by bonding this anchoring fleece onto the load-bearing substrate. A tile adhesive suitable for the format and application of the tile is then applied on top of the mat, and the tiles are set in the thin-bed method. Because the adhesive is mechanically anchored into the cut-back grid cavities, there is no direct bond between the covering and the substrate. Consequently, deformation stresses originating in the substrate are not transferred to the surface. The result: no surface damage.
Although this uncoupling system protects the surface, movement joints are still required. The two work in conjunction with each other to produce a complete systems solution. Stress-relieving movement joints are still needed within the surface to absorb thermal expansion and contraction of the tile.