Architects and contractors know how stressful it can be when things go wrong. The way to avoid such stress over tiling installations in is to ensure the tiles themselves are free from movement stresses. Ceramic and stone
tile installations can be subjected to a variety of stresses leading to tiles bulging, cracking or becoming detached from the substrate. IAN KNIFTON, Technical Manager at Schlüter-Systems Ltd, world market leader in tiling solutions, says the correct placing of appropriate movement joints will absorb many of these stresses, preventing damage. Q: What do movement joints do?
A: A movement joint is a stress-relieving profile, compensating for the movement of tiles and/or the substrate. Without them the shear stress builds up between the
tile and the screed, causing debonding, bulging and cracking. Therefore, stress-relieving joints are an essential part of any tiling installation, and should be incorporated at the design stage.
Q: How do they work?
A: Movement joints create a
tile field which moves independently from those around it. They should be included at set distances in floor tiles in accordance with recommendations from the British
Standards Institution (BSI), which say 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.
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 asked of them.
Tilers, architects and specifiers generally know that movement joints must be used, the problem is often the lack of knowledge as to which joint is right for which application. TIPS ON SELECTING THE CORRECT MOVEMENT JOINT 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.
Generally aluminium is ideal for light commercial use, with brass and stainless steel needed for heavy 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.
However, on a number of occasions Schlüter-Systems Ltd. has seen where damage has still occurred to the
tile, and to the profile -- because it's not been fitted correctly.
Q: What is the most common reason for installations failing, even when movement joints have been fitted?
A: Assuming that the correct joint has been chosen for what is required of it, namely aluminium for commercial use, with brass and stainless steel needed for heavy duty commercial and industrial flooring -- and that they create
tile fields of no more than ten metres in each direction, then the main reason for failure is that they're not installed correctly.
When fixing movement joint profiles it is important that the profile is either fitted flush with the finished surface, or actually placed up to 1mm below. If it's raised, however slightly, the profile can't disperse or absorb the point load correctly, and damage to the joint and the
tile usually occurs.
Also, of course, if there are wheeled loads going over the top of it, they can easily damage the edge of the profile.
Q: If the profile is damaged, does the whole movement joint have to be replaced?
A: If the anchoring legs become damaged, you will need new ones. However, some movement joints, such as the Schlüter-DILEX-KS profile, have a replaceable synthetic rubber insert which is the part of the joint that actually absorbs and disperses the movement. If it's only this rubber insert which has suffered damage, these can simply be levered out by inserting a screwdriver, and rolling a new one in place.
Another benefit of replaceable rubber inserts is that they can be used to improve the aesthetics of an installation. On a number of occasions the architect has asked that once the movement joints are installed, the replaceable rubber insert is taken out and put back in staggering the joints in the anchoring legs. This can make them look almost invisible in the application, improving the appearance of the finished surface.
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.
Q: Do I need to place movement joints in the
tile covering directly above any movement joints within the substrate, as this will destroy the
tile design?
A: Yes, you must place them directly over any existing joints in the substrate. We're often asked if surface joints can be offset by putting them just a small distance away, but this is rarely possible.
On many occasions we've seen designs where installers have offset the movement joint in the surface only by millimetres from the one in the screed, and the ceramic
tile or stone covering has cracked.
The surface covering of
tile or stone will crack because they're rigid, and you're installing them over a flexible substrate. By lining up the movement joints in the surface with the joint in the substrate you're creating individual areas where the substrate and surface move together, preventing cracking.
If it's not absolutely over the top, problems do occur. There are some ways round it occasionally, depending on the type of joint in the screed, but you would need to take expert advice from movement joint specialists as to whether it's possible in specific, individual applications. As a rule of thumb, though, they must be directly over the top.
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.
For further information and advice about solving tiling problems, contact Schlüter-Systems Ltd., on 01530 813396.
Using the schluter joints is easy....and can be bought from any CTD store....
