Sweden's SP tests buildings for warped cladding

Homoblastic marble: its microstructure means that it will lose strength and bow.

The idea of the device, Bow-meter, came about after the research team wanted a technology that could estimate the magnitude of the problem of warping on site, so that they could follow annual changes without taking panels down and bringing them to the lab every time.

“The project started to deal with a very real problem and a visible one too, the bowing of facade panels of marble,” said Björn Schouenborg, the coordinator of the project at SP. “Later we found out that the bowed marbles lost a lot of their original strength. Still later we found out that some of them lost strength without bowing – even worse because you can't see that there is a problem until it may be too late.”

Stone has long been used in the construction of buildings. More recently thin layers of stone, such as marble, have been used to cover and beautify the outside of buildings, including many landmarks across Europe. Many of these stone claddings have not withstood the test of time. Deterioration, from bowing and warping to total failure, has raised concerns over safety as well as corrective and preventive maintenance.

Schouenborg said the benefit of the Bow-meter, a digital device that can be connected to a PC for quicker measurement and recording, is that it does not harm the building façade and it is inexpensive. It can also alternatively be applied to screen stone intended for use in cladding. He added the device could be used by “anyone with a marble clad façade – the building owner or caretaker”.

The device was produce by Schouenborg, Bent Grelk from Ramboll in Denmark and Jan Anders Brundin, of Jan Anders Consulting in Sweden, after an earlier prototype from SP turned out to be too heavy for one person to operate on their own.