Drying behavior of masonry units

Before occupants of buildings affected by water damage can safely return to their homes, they have to wait until the walls have completely dried out. To predict how long this will take, and to choose the best drying methods for different wall structures, researchers at Fraunhofer IBP have conducted laboratory tests on numerous different types of masonry units.

© Fraunhofer IBP

Infiltration of water from above into a tiled section of an aerated concrete wall.

Wet walls contain a lot of water that not only reduces their insulating properties but also increases indoor air humidity levels and encourages the growth of mold on exposed surfaces. Hence the importance of enabling waterlogged walls to dry out as rapidly as possible, using specialized drying equipment if necessary. But the drying method is not the only decisive factor: the drying rate also depends on the composition of the wall. To establish a drying curve and predict how long it will take for different wall structures to dry out, different material characteristics were defined on the basis of laboratory tests and climate chamber simulations. In addition to traditional building materials such as clay bricks, expanded clay aggregates, porous concrete blocks, and pumice concrete, more modern products designed to improve insulation performance, such as composite blocks filled with mineral fibers or perlite, were included in the tests. Another factor that influences the drying behavior of walls is surface plastering. To evaluate this effect, additional laboratory tests were carried out on plastered and bare walls, and on walls with a damaged plaster surface.

Prior to the drying tests, the chosen samples of different masonry units were first left to soak in a water tank to determine how much water each of them is capable of absorbing. The samples were then dried in climate-controlled chambers under constant environmental conditions and weighed at regular intervals to establish their respective drying-rate curves. Other characteristics such as water absorption coefficient, diffusion resistance factor, and moisture storage function were also determined in the laboratory. By feeding the obtained material-specific data for different masonry units into various hygro-thermal simulation programs, the researchers were able to simulate the drying behavior of different wall structures under a wide range of conditions. The results of the simulations served as a basis for more detailed investigations into the efficiency of different drying methods as a means of speeding up the drying process.

The test results reveal that the different masonry units vary widely in their drying behavior. But the factor with the greatest effect on the drying rate turned out to be plaster rendering.

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