Prague National Theatre - Prague, Czech Republic

As part of extensive restoration work on the Prague National Theatre, Kärcher was involved in cleaning the building, which dates back almost 130 years: the family-owned company supported the project with its experience and cleaning technology to gently remove stone-damaging dirt from the theatre's facade. The restoration project is being carried out by the local company ART KODIAK s.r.o. Work was begun on the north facade; the restoration is due to be completed in four years.

The ornate facade of the theatre, which was built between 1868 and 1881 in the Neo-Renaissance style, consists mainly of sandstone and plaster surfaces. It was cleaned between 1977 and 1983 during its first restoration and painted with – as would later transpire – an unsuitable acrylic paint, which is now being removed as part of the current restoration project. Dust, organic matter and emissions residues have also been deposited on the surface since it was first cleaned. The black dirt and encrustations, which are very stubborn in some places, not only detract from the external appearance of the building, they also damage the natural stone and must therefore be removed.

In collaboration with the owner, restorers and representatives of the heritage conservation authority responsible for the project, Kärcher application engineers carried out tests before beginning the restoration work to establish the best cleaning method. A particle blasting procedure (dry), with calcium magnesium carbonate (grain size 5 - 300 µm, Mohs hardness 3 - 3.5) as a spray agent, is being used for the work. Hard-to-reach areas on the delicate stonemasonry are being treated with a chemical paint stripper and then cleaned with the hot water high-pressure cleaner.

Kärcher is providing the Prague National Theatre, the organisation responsible for the restoration, with the necessary machines, hot water high-pressure cleaners, blasting systems, wet/dry vacuum cleaners, and cleaning and spray agents.