Moisture and especially salt can give rise to the deterioration of porous building materials. Two major effect of salts are salt efflorence, which can cause both visual and structural damages, and the corrosion of steel in concrete structures, which can cause structural damages. Therefore a detailed knowledge of moisture and salt transport is essential for understanding the durability of these materials. For measuring the combined moisture and ion transport often destructive methods are used. These methods usually involve drilling or grinding of the sample, gravimetrically determining its moisture content, and chemically determining its salt concentration. These methods have the disadvantage of destroying the sample, which complicates any time-dependent measurements, and usually lack sufficient resolution (of the order of 10 mm).
By using NMR both the moisture and the Na profile can be measured non-destructively during absorption of a salt solution. The absorption of a 4 M NaCl solution in calcium-silicate brick was investigated by NMR. The resulting measured profiles are given in figure 1.

Figure 1: The moisture (+) and Na profiles ( ) measured during the absorption of a 4 M  NaCl solution. The dashed curves through the points are meant as guides to the eye, whereas the times are given as an indication of the elapsed time.
As can be seen for moisture a sharp wetting front is observed. However, the Na profiles clearly lag behind the moisture profiles. Almost no Na is observed near the wetting front. This is due to the interaction of the Na ions with the pore surface.