Facade Symptoms Related to Steel Corrosion
By: James Monahan
Whether we are performing a FISP (formerly Local Law 11/98) inspection or preparing a building envelope survey, we are constantly inspecting and documenting visual defects or deficiencies in building facades. But, we are also responsible for attempting to detect the underlying causes of these conditions. Vertical cracks at corner columns, rust jacking at window lintels, and displaced or shifted masonry can often be attributed to corrosion of the structural steel members embedded in the facade.
If the exterior structural elements of a building are not properly waterproofed, moisture will eventually infiltrate the facade through deteriorated mortar joints and face brick. When water and oxygen come into contact with steel, corrosion begins to occur. Essentially, the iron (Fe) atoms that are a primary component of steel will lose electrons, becoming positively charged ions that attract negatively charged ions like water and oxygen. This attraction results in a chemical known as iron hydroxide. As iron hydroxide continually reacts with oxygen, it results in hydrated iron oxide, better known as brown rust. The more hydration cycles the steel experiences, the more the steel will rust. When enough rust sets in, the steel will flake off in layers, expand and build up pressure against the exterior wythe of masonry. As the pressure builds, the exterior mortar joints and face brick will begin to shift and crack.<
Building Envelope Consultants will recommend and design repairs to address these types of deficiencies, along with the structural steel issues that caused them. Corner column rebuilds, lintel replacements and face brick replacement are a few of the typical repairs detailed in the Consultant’s design. Each repair requires that a Contractor demolish the exterior masonry, and expose the structural steel. The Contractor must always install temporary shoring wherever masonry is unsupported. After the steel is exposed, The Building Envelope Consultant inspects it to determine the extent of deterioration or section loss, and whether the expertise of a Structural Engineers is required.
In many cases, common cost-effective repair options can be employed. These might include replacing a loosely laid steel lintel, or mechanically removing corrosion from a steel column or beam before priming, painting and waterproofing the steel member. These scenarios are ideal when compared to those that must address more serious damage to the structural steel.
Building Envelope Consultants must be particularly diligent when inspecting the columns, braces and spandrel beams that comprise the structural system of a building. The extent of damage may necessitate that a licensed Structural Engineer be retained to perform inspections and design repairs. Rusting that’s lead to section loss, deteriorated or pitted flanges or webs, corroded or cracked structural welds and severely corroded bolts are examples of this type of structural damage. While structural repairs and steel beam/column member replacements are much costlier than routine façade maintenance and repairs, they are absolutely crucial. Failure to maintain and monitor the overall structural capacity of a building can lead to catastrophic consequences.
Once steel members are inspected and reinforced as necessary, moisture must be mitigated to inhibit future corrosion. Typically, a waterproofing membrane is installed on the steel prior to replacing the exterior wythe of masonry. Grace Perm-A-Barrier membrane, with Bituthene Liquid applied at all seams and terminations, will prevent moisture from coming in contact with the steel. Weep vents should also be installed at the bottom of the new masonry to allow moisture to escape, rather than build up behind the exterior wall. In addition, Building Envelope Consultants should inspect roofs to check if they are watertight and properly pitched. All drains, gutters and downspouts should be clear, as well. It’s imperative that the roof system moves water away from the building. The longer water ponds, the higher the likelihood it will infiltrate the building envelope.
In New York City, buildings that are 6 stories or less are currently not required to participate in the FISP program; however, these buildings are still subject to aging, weathering and water infiltration. Without periodic building envelope monitoring, façade and possible structural deficiencies can go undetected and pose safety issues. To ensure a building is watertight, and more importantly safe, Owners and Property Managers should retain the services of a Building Envelope Consultant to perform inspections, provide repair and maintenance recommendations and oversee any façade or roof related construction projects.