Restoration of aging masonry buildings

Spalling

Spalling of brick masonry is a very common deterioration mechanism in cold climates and most concerning to building owners. Spalling brick can potentially result in falling hazards that increase liabilities for owners. Prevention of spalling brick starts with sound design and quality installation. However, this must be supplemented through the life of the building with diligent review and rehabilitation practices.

Spalling occurs as a result of water intrusion into the brick combined with freezing temperatures that causes the water to expand and pop off the face of the brick unit (Figure 7).

It also exacerbates the rate of failure of adjacent bricks as they are now more prone to water ingress and future spalling. Additionally, spalling carries an increased potential for esthetic consequences ranging from minor localized brick units to significant large areas of painted brick.

Best practice #4: Liabilities associated with spalling brick are significant. Have all noted locations of brick spalling reviewed to determine causes and consequences.

Regardless of the duration of time an owner intends to carry a property, whether a couple of months awaiting redevelopment or an intent for long-term building ownership, the liabilities from deteriorated brick masonry far outweigh the costs of an assessment by an engineer. Ownership is therefore strongly recommended to investigate and also protect the area of spalling brick immediately.

Spalling that occurs as a result of freeze-thaw deterioration requires the presence of the following two conditions:

• a material that has reached critical saturation; and
• freezing temperatures.

The outer wythe of historical masonry buildings reach critical saturation several times over their lifespan during periods of freezing temperatures, yet remain in sound condition. The primary reason for this is the masonry has not reached freezing temperatures as a result of significant heat loss from the uninsulated mass wall building. As energy becomes more costly, an increasing number of owners are choosing to insulate their historic mass masonry buildings. Due to heritage designations and esthetic concerns, these owners are constrained to only apply insulation to the interior of the exterior wall. Further, these insulations tend to be vapour closed (e.g. closed-cell sprayed polyurethane foam [SPF]) to reduce wall thickness. This inhibits the drying of a mass wall previously exposed on both sides. This type of insulation reduces heat flow from radiation and drying from convection (Figure 8). This may lead to deterioration of the exterior masonry and embedded wood elements, a consequence often overlooked during analysis of insulation options (Figure 9).

Best practice #5: Prior to insulating the interior of a previously uninsulated building, complete site-specific hygrothermal analysis of the exterior wall assemblies in order to confirm their capability of accommodating reduced temperatures.

Hygrothermal modelling software can be employed to understand the temporal impacts to temperature and moisture flows as a result of the proposed insulation system. The software is capable of using site-specific data based on material testing to develop a model that is a reasonable simulation of reality. For these models to be applicable, it is imperative the existing masonry be tested and used as the basis for the modelled masonry performance parameters because critical saturation values for masonry can vary widely.