Water Penetration in Solid Clay Brick Masonry and its Mitigation by Repointing

Clay brick masonry façades are widely used because of their extended durability and aesthetic appeal. They also offer good protection against wind-driven rain (WDR), one of the most common moisture sources in Northern Europe. In clay brick masonry, WDR is associated with elevated water content and the possibility of water penetration, which may negatively impact the hygrothermal performance of building envelopes. Maintenance measures are thus recommended to address elevated moisture content and water penetration associated with WDR, where repointing is a commonly used maintenance technique. Presently, in Sweden, repointing is typically scheduled every 40–50 years from the construction of the building, regardless of the condition of the façade. Given that repointing is a labor-intensive and expensive undertaking, there is a pressing need for a systematic approach to evaluating the necessity for repointing based on rational grounds.

Within this Ph.D. project, a new laboratory test setup is developed to study water absorption and penetration in clay brick masonry. The key feature is to enable uniform water spray exposure at considerably lower water spray rates than in existing test setups while continuously recording both the amount of absorbed and penetrated water. The developed test setup is used in four experimental campaigns to study the interaction of clay brick masonry exposed to water spray.

In the first two experimental campaigns, two series of clay brick masonry specimens without known cracks, built with two different types of bricks and three different mortar joint profiles, are exposed to water spraying. The obtained results indicate that in clay brick masonry without known cracks, water penetration starts when the masonry is nearly saturated (average moisture content above 90% saturation level). As there is a lack of consensus regarding the quantity of WDR penetration through clay brick masonry claddings and the appropriate methodology for incorporating penetration in hygrothermal analyses, a novel water penetration criterion in clay brick masonry is introduced.

As cracks provide low resistance pathways for water penetration, clay brick masonry specimens with different crack widths, created artificially, are exposed to water spray in the third campaign. Subsequently, in the fourth campaign, specimens tested in the third campaign were repointed and tested once again to study the effect of repointing on water absorption and penetration in clay brick masonry. The results indicate a reasonable correlation between the crack width and the average water penetration rate. Further, a strong correlation is observed between the saturation level and the start of water penetration; the larger the crack width, the lower the saturation level at the start of water penetration. The obtained results suggest that repointing can effectively reduce water penetration in cracked clay brick masonry.

Finally, the experimental results are implemented in hygrothermal simulations, providing an understanding of scenarios where repointing may mitigate moisture risks in building envelopes. The results of the simulations suggest that repointing has the potential to notably decrease the mold risk of timber frame walls and reduce the moisture content of autoclaved aerated concrete (AAC) walls. The positive effects of repointing are particularly pronounced when the brick veneer exhibits signs of poor workmanship or visible cracks, especially when walls are exposed to high WDR loads.