An accurate choice of a re-pointing mortar is fundamental for successful restoration work. The use of an incompatibel mortar can affect the moisture transport inside the masonry and consequently lead to a different drying behaviour of the various materials: this can cause damage or speed up the decaying process already present in a masonry wall. For this research we have measured the moisture transport in a small masonry samples with dimensions of 50x30 mm and a thickness of 30 mm. In figure 1 the experimental set-up is given.

Figure 1: The experimental setup

In this experiment dry air was blown over the left side of the sample. The experiment lasted 24 hours. Using a backward projection method the moisture distribution was determined for every hour.  In  figure 2 the measured 2D moisture distribution is plotted for various times.

Figure 2: The 2D moisture distribution as  measured during a drying experiment, at 0, 1 ,2 ,3 ,4,8, 16 and 24 h.

At t=0 the different materials show a moisture content related to their porosity. As can be seen in this case the cement pointing mortar is drying first. The bedding mortar is dry after 16 hours aftes which the bricks ared dried.
In figure 3 another example is given of the drying of a sample. In this case the drying was measured for a sample saturated with water and a sample saturated with a 4 M NaCl solution. As can be seen the drying is very similar in both cases only that the drying is much slower in the case of NaCl.

Fig. 3: The 2D moisture distribution as  measured during a drying with: (a) pure water; (b) 3m NaCl solution.