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Schlüter-Systems Movement Joint Series, Technology Makes Movement Joints Obsolete
Architects, specifiers and end-user consumers often attempt to dissuade flooring contractors from putting movement joints in the correct places in tiled flooring, because they say it detracts from the visual appeal of the overall installation.
In many cases there can be some leeway as to the precise positioning of surface movement joints. However, there is no leeway at all where there are also movement joints in the substrate.
But, as Ian Knifton, Technical Manager at Schlüter–Systems, explains, advancing technology is eliminating the need for movement joints in the screed, which gives greater flexibility in surface tile design.
Movement joints in the tile covering must be placed directly over any existing movement 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 contractors 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.
If it’s not absolutely over the top, problems do occur. There are some ways around 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 the specific individual application. As a rule of thumb, though, they must be directly over the top.
The surface covering of tile or stone will crack because it’s rigid, and you’re installing it 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.
However, advancing technology is actually changing the way subfloors and screeds are constructed. If your project is at the design stage you could install a modular screed system which doesn’t need movement joints in the substrate at all.
This type of specialist screed underlayment system – known as Schlüter®-BEKOTEC produces a thin, stable screed, without the need for movement joints or reinforcement. Then it wouldn’t matter so much where your surface movement joints are fitted, as long as they fall within British Standards Institution guidelines.
Because there are no movement joints in the screed requiring surface joints to be placed immediately over the top of them, there is much greater flexibility in the tile design. There is no need for the surface to follow movement joints in the screed, or extend surface movement joints down into the screed.
Both conventional cementitious or anhydrite screeds can be used over the underlayment. The screed system will not warp, and no continuous cracks will appear. The reduced screed mass results in a weight of approximately 57 kilograms per metre cubed, and a reduced screed quantity which has a positive impact on the static calculations of new construction or refurbishment projects.
Next month - we look in detail at the technology behind this system, and how it overcomes the problem of meeting building regulations when tiling onto heat and sound insulation.
For more information contact:
Stewart Bint
