TEGO® Phobe from Evonik Protects Heritage Buildings against Dirt and Decay

The interior of the late Gothic Willibrordi Cathedral in Wesel, Germany, is a picture of perfection. Sunlight streams from dozens of antique glass windows into the basilica, illuminating the altar table and the organ. Mighty columns and arcade arches support the edifice; wooden decks and slate flooring lend a splendid, solemn air. But on leaving the building, it is immediately obvious how time has slowly but inexorably ravaged this Wesel landmark, with algae and lichens covering parts of the basalt base. Dust and dirt from the air have over the centuries discolored some windowsills and cornices to gray or black. But now a product from Evonik’s chemistry labs will eradicate the marks of time and also protect the Cathedral over the next few decades.

TEGO® Phobe is a special active ingredient for formulations to protect large buildings or small single-family houses against water. Its special feature is that in silicone resin paints and waterproofing formulations the product repels rainwater; it does not, however, seal the stone but allows water vapor to escape from the interior to the exterior. TEGO® Phobe is industrially available as a milky emulsion or solution, which is then formulated to the end product, silicone resin paint or impregnation.

Ten cycles in the soiling machine

A quick round of the laboratory gives an excellent insight into the expertise behind a product like TEGO® Phobe. New formulations for silicone resin paints and impregnations are developed in serial trials and are compared with competitive products to market standards. Each stone is investigated in detail to determine, for example, how much water it takes up, and how much soiling occurs in the course of time. Using special cameras and computers, lab technicians measure the water repellency of a coated surface.

Individual samples are then treated in an adapted industrial dishwasher, where they are flushed in ten cycles with a mixture of water, tar, and soot. This is the soiling machine lab technicians usually call. It allows a quick simulation of how silicone resin paints will stain over a period of several years.

Preventive protection against algae and lichens

TEGO® Phobe has been used on Willibrordi Cathedral before the end of 2008. The Wesel cathedral was severely damaged in the Second World War and then restored over several decades. This work naturally used the old plans and the traditional building materials of the Middle Ages, including the Oberkirchen sandstone. "This stone is indeed very strong," says the master builder, Prof. Dr. Deurer, "but unfortunately it rapidly takes up dirt from the air and becomes discolored." The pale sandstone turns gray and black. Additionally, algae and lichens can attack the mortar in the interstices and crack it; sooner or later, moisture penetrates into all masonry.

“Construction is a lifelong battle against water,” says Prof. Dr. Deurer from experience. Water moves upward from the foundations; piping becomes leaky; the masonry “sweats” in summer; and in winter the water freezes and expands, developing tremendous explosive force. TEGO® Phobe not only permanently protects the facade and arrests the discoloration process; formulated with the right auxiliaries, it also prevents the growth of algae and lichens. “This would be an ideal solution for our church,” says the master builder, “because frequent cleaning of the facade is simply too expensive.”