Volume 4, Issue 1

One of the most common reasons to restore an old (historical) building is the damage of the masonry and the external rendering due to moisture. For the analysis of the damage mechanism and the restoration of the building, experience and specific knowledge are needed. The first step to realize a successful restoration is the determination of the actual condition of a building by appropriate analysis and the deduction of the damage of the damage mechanisms. If rising damp is a causing mechanism, different restoration concepts can be considered. The choice of the final concept is mainly influenced by the cost, aspects of preservation of monuments and the future usage of the building. For the restoration of the School Building Heinrich Bosshard at Zurich-Schwammendingen, the rising damp was stopped by making a horizontal saw cut into the rubble masonry.

Lately, diffusion open underslating sheets (USS) have been inserted to pitched roofs increasingly. These sheets allow moisture to escape from the construction while they remain waterproof The conventional procedures to determine the water vapour diffusion resistance of the USS result in high deviations of the test results depending on the test methods and the boundary conditions. For this reason, an ordinary, non-ventilated roof-system with insulated rafters was tested in consideration of the different s d -values. The characteristic sd-values of underslating sheets based on experiments according to DIN 52165 were assumed to be constant and dependent on the humidity. The calculations prove that a serious danger to the roof-systems (almost by a factor of 10) is possible considering the chosen s d - value of an USS. Thereupon recommendations for an experimental laboratory method of the 'real' s d -value were made in order to be able to judge the roof-system in a realistic way.

To reach a broad application of computation methods for the calculation of the moisture balance in building components, simplified methods for the determination of the necessary hygric material properties are required. Such an approximate method has already been developed for the determination of the transport coefficients for liquid capillary absorption. The drying process mostly shows significantly smaller liquid transport coefficients. A new method is presented to determine approximately these coefficients from results of a simple drying experiment. A comparison of calculated results using this approximation and exactly determined coefficients shows only moderate and acceptable deviations from reality.

The interaction between micro-organisms and natural stone surfaces has been studied in great detail in the past. The destructive mechanisms of micro-organisms can be roughly subdivided into (a) chemical attack and (b) physical attack. Microorganisms may physically destroy the structure of stones by creating an inter-granular swelling pressure. Recently, it has been shown experimentally that black spots formed by yeast-like fungi lead to a local temperature increase by selective absorption of solar radiation. The maximum temperature observed for clean marble surfaces remained below the maximum temperature observed on inoculated surfaces. As a consequence, thermal dilatation of inoculated marble was shown to be more important. Destruction of the heated stone occurs predominantly if there exists a thermal gradient. In this paper, temperature distribution in clean and stained marble plates have been simulated numerically. Thermal eigenstresses have been determined. It is shown that tensile stresses of up to 5 N/mm2 can be expected. This may cause damage in weak zones of the surface. A sudden driving rain leads to much higher stresses. Cyclic thermal loading may eventually destroy the surface by fatigue.