Visual observations are not sufficient to determine the cause of failures in masonry walls. However, visual observations, combined with technical knowledge, provide a good direction for further investigation. In the Pacific Northwest, with the predominance of rainy winter weather, the effect of moisture saturation on masonry walls is readily apparent. Moisture is the primary cause of masonry deterioration. Horizontal surfaces will accumulate organic growth, mortar and masonry surfaces show rain water runoff patterns, and any discontinuity in roof runoff systems quickly cause further deterioration to the masonry walls. Severe masonry deterioration does occur in the northwest but its occurrence is considerably less dramatic when compared to harsher winter climates in the Midwest and East. For instance, brick spalls due to freeze thaw effect are a rare occurrence in the northwest.

When severe deterioration of masonry walls is not a prevalent condition, what other non-visual processes are employed to determine the cause of deterioration? Two common techniques, well known to historic preservation professionals, are non-destructive testing (NDT) and material testing in the laboratory. NDE methods include RILEM tube water absorption tests, metal detector scanning, video scopes, infra-red photography, ultra sound testing, ground penetrating radar, and in some cases, x-ray diffraction. Common laboratory testing include petrographic examination, electron microscopy, and Fourier Transform Infrared (FTIR) methods.

FTIR, when combined with the diagnostic RILEM tube field test, in particular is an effective evaluation to determine if masonry sealers have been applied to a wall surface impeding the capillary evaporation of trapped water. RILEM tests also provide an observation of a masonry wall’s initial rate of absorption under wind driven rain circumstances. Petrographic analysis of both masonry and mortars determines the material composition and will identify harmful natural elements and harmful additive elements like salts.

A common misconception in the northwest is that surface spalls are a result of freeze thaw cycles. Freeze thaw susceptibility can only be determined through laboratory testing. Visual observations are insufficient to conclude masonry spalls resulted from freeze thaw forces. Since freeze thaw tests are graded either pass or fail, further tests methods are typically required for additional diagnostic evaluation. More likely sources of surface spalls are hard Portland cement mortars which exceed the strength of the masonry, salts introduced into the masonry through incorrect material selection, or surface sealers impeding the evaporation of water and thus creating a saturated sub surface layer which will freeze. (It is important to distinguish that the masonry unit may not be susceptible to freeze thaw but rather the sealer creates a dam like effect inducing a layer of water subject to freezing)

By combining visual observations with NDE and lab testing, most surface masonry deterioration can be determined and thereby implement proper repair, maintenance, and protection methods.

Written by Peter Meijer AIA, NCARB, Principal