Natural stone in “jura grey” in foyer and gallery:

Many floors in the Congress Center Heidenheim, a.o. the foyer at the ground level, the wide staircase leading to the gallery and the gallery itself, are covered with natural stone in “jura grey”. The areas in the entire building sum up to about 1600 sqm plus 350 running meters of tread and risers. To meet the requirements as to resistance of the floors (5 N/mm²) it was decided to install natural stone flags, 2 cm thick. The surface of the natural stone - which is formed from flags of different lengths and a width of 20, 25 and 30 cm according to the specification by the architect office Zürn, Dasch, von Scholley - was diamond-blasted and brushed. This surface treatment gives the originally rather soft sedimentary rock a rustic and vivid surface. Inevitable signs of handling due to a mishap at the buffet or when walking on the surface remain practically invisible because of this surface structure.

Starting with the stairs:

On May 19, 2009 the comprehensive natural stone works in the CCH started with the main staircase. Three employees of company Mack and the boss himself were engaged in daily laying 6 steps of the staircase with an average width of 10 meters. They used the bedding mortar PCI Carrament grey especially suitable when working with natural stone. Speaking of the daily output it must be considered that 120 recesses for lights had to be created into the treads. The natural stone surfaces of the intermediate landings of the main stairs were bedded in trass mortar. The work in all staircases was completed on June 9, 2009 with about 350 running meters of treads and risers.

Laying flags in the foyer in stages:

The natural stone covering of the floors rests on a flowable screed installed in February 2009. After the first CM measurings in April 09 the area was such aerated that the required value of £ 0.5% was reached at first in the lower foyer in May 09 enabling to start the tiling work. Unfortunately the planarity of the installed screed did not meet the requirements all over leading to delays in the work progress. PCI employees took samples as to adhesion with “very good” results. The uneven surfaces required an additional application of bedding mortar and PCI therefore recommended to prime the surfaces with PCI Gisogrund 404. The employees of company Mack – all educated floor tilers, mosaic tilers and/or stonemasons and stone sculptors – started to lay the flags in the sublevel foyer (approx. 486 sqm) subsequently to the tiling works in the staircases and the access to the underground parking on June 9, 2009. The surface was rough-ground at first and – as recommended – primed with PCI Gisogrund 404 in two layers. Then the natural stone was laid with PCI Carrament grey. The work was completed by the end of June followed by the tiling works in the gallery and the ground level foyer (approx. 578 sqm).

Georg Mack: “A layout drawing was made up for the floor in the main foyer of the ground level. The area was divided in trapeziums which were supposed to be separated from one another by profiles. This solution played into our hands because now we could make separating joints on an area of 51 x 11 meters across the tiling direction and without affecting the overall picture.” All joints were sealed with silicone by the specialized company Mikelopoulos, mostly in the evenings and at the weekends. Initial cleaning and impregnation of the natural stone floors by employees of company Lehmann of Karlsruhe was mainly done at the weekends. Employees of company Mack covered the floors such prepared with a special fleece which is breathable and permeable to vapour. This protection helped let the newly laid natural stone dry up without staining. Hard wood fibre building boards, 3 mm thick, were placed on top of the surface and held in place by means of adhesive tapes. Due to this protection the surfaces could be exposed to pedestrian traffic and to air-tyred or soft rubber tyred equipment.