The paint testing machine

1/4 images   The testing machine   Die paint (below) is bent until cracks form.

1/4 images The testing machine Die paint (below) is bent until cracks form. (Photo: TU Wien, free to download and use) Die paint (below) is bent until cracks form. (Photo: TU Wien, free to download and use)

How can you prevent cracks from forming after painting? TU Wien has recently patented two new measuring processes that show which paint is best.

It’s a familiar problem for anyone who has renovated a house or flat: no building is a perfectly rigid body. Walls and ceilings can move slightly over time, which often leads to cracks in the paint on the walls. Until now, there has been no reliable test method for measuring whether a wall paint is elastic enough to permanently cover cracks. Researchers at TU Wien have developed two different processes that can help with this, both of which have now been patented.

No sooner is the renovation work complete than more work is required

"If you want to prevent cracks from developing in the wall, you need to select the right materials - from filler through to interior wall paint. Until now, we have had to rely primarily on experience," says Dr Aleksandar Radoevski. "Time and again this causes unsightly cracks to develop in the walls of newly renovated buildings, so further work is required after just a few months."

Aleksandar Radoevski has therefore developed methods to reliably characterise the elastic behaviour of interior room coatings and coating systems; these can accurately predict which coatings will enable you to prevent cracks to the greatest extent possible. His work, which he carried out at the Institute of Construction, Structural Dynamics and Building Technology at TU Wien, was part-financed by the City of Vienna University Jubilee Foundation (Hochschuljubiläumsstiftung) and has already been recognised with a Christiana Hörbiger Award in 2018.

Rapid test or more detailed test

For Radoevski’s ’cantilever beam elasticity measuring process’, the wall paint is first applied to a beam in a precisely defined way. After that, the coated side of the beam is slowly stretched for a period of five to fifteen minutes. A camera takes two high-resolution pictures per second from this side of the beam - this enables the user to precisely assess at what degree of expansion cracks occur. The decisive point is when a crack reaches a width of 0.2 mm - this is the limit from which a crack is considered to be a defect according to the relevant DIN standard.

"This test method is straightforward and can be carried out in next to no time," says Aleksandar Radoevski. "This is perfect for quality control in series production, if, for example, you are a paint manufacturer and want to check that the paint still has the planned elasticity." This method does have a downside, however: The beam that the paint is applied to needs to be made from a specific carrier material. Ideally, the material used should be as similar as possible to the wall you want to paint. Sometimes, however, you might want to be able to examine the paint yourself, fully independently of the carrier material. A solution has also been found for this.

"We investigated how to create a sample of just the paint, which can then be examined in an expansion test without the need for a carrier material," explains Aleksandar Radoevski. "This method is somewhat more cumbersome and takes longer, but is also more precise."

Reduced renovation costs

Both processes have a patent pending in association with Research and Transfer Support at TU Wien. "Using this process, it is now possible to find a sufficiently elastic wall coating that is ideally suited to a specific application," says Radoevski. "This not only enables higher quality crack repairs in buildings, it also makes them more cost-efficient." The two methods therefore bring huge benefits for both paint manufacturers and test institutes.

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