Elastomeric Coating: More than Just Paint - by Brian DeFrias
Many older multi-residential condominium buildings in the London and surrounding areas are constructed with concrete and masonry exterior walls and cladding systems. These materials were (and still are) widely used for this type of construction because of their architectural appeal and performance in the Canadian climatic environment. There is a downside to using this type of exterior wall system however, in that both concrete and masonry are porous materials. If the design of the wall does not allow for absorbed water to be properly drained or dried out, the trapped moisture within the material may lead to several issues which can worsen over time. These issues range from visually unappealing (such as weathering and moisture staining of the exterior wall face) to structural and safety concerns (such as cracking and spalling caused by freeze/thaw cycles). So how do we protect these concrete and brick masonry buildings from the damaging effects of water penetration? There are numerous over cladding options available such as metal siding or Exterior Insulation and Finish Systems (EIFS), but these can be quite costly and drastically change the appearance of the building, which may not be desired. What about just coating the exterior? Careful thought and planning need to be put into this option or you may be doing more harm than good! Elastomeric Coatings vs. Paints Elastomeric coating often gets used interchangeably with exterior paint, but they are two very different products. Simply put, paints improve aesthetics only, and coatings improve both aesthetics and performance. Elastomeric coatings are basically paints with a purpose. Here are some key differences between the two:
Brian DeFrias, C.E.T., BSS is the Manager of Building Sciences at IRC Building Sciences Group and can be reached at bdefrias@ircgroup.com or 519-281-3754.
Thickness:
One of the main differences between the two is the thickness in which they are applied. Paint leaves a very thin film on the surface whereas elastomeric coatings are applied much thicker – typically 6 times thicker than paint.
Flexibility:
While most typical paints dry to a brittle finish, elastomeric coating have elongation (stretchiness) and memory characteristics which allow it to tolerate movements and bridge hairline cracks in the substrate it is applied to. In other words, if the wall experiences thermal contraction / expansion movements, the coating moves with the substrate without cracking or permanently deforming.
Breathability:
Elastomeric coatings are unique in that they are barriers to water in its liquid form (rain, snow, etc.) while at the same time having permeability to allow water in its gaseous form (moisture vapour) to pass through without affecting the films adhesion to the substrate. This breathability is very important to not trap moisture within the material which can cause continued freeze/thaw damages to occur. Trapped moisture vapour could also result in peeling or blistering of an incorrectly chosen exterior paint finish as the pressure forces ‘push’ the paint away from the substrate.
CASE STUDY: More Than Meets The Eye
Building Summary: 10-storey high-rise condominium building located in London, Ontario. Brick masonry veneer with concrete block backup wall construction type built circa 1990.
The Problem: This building had a history of brick masonry spalling and cracking issues leaving the corporation with a costly forecasted repair program for the duration of the building’s remaining service life. In addition to the failing brick issues, several of the residents were reporting water leakage along the top of their large living room / dining room windows.
10 — 2020/2021 - 2
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