The High Cost of Improper Drainage and Ventilation in Adhered Masonry Walls
Today’s adhered masonry veneer walls are typically more vulnerable to moisture problems than older “thick mass” masonry walls or today’s masonry cavity walls. The reason is simple – most of today’s typical masonry veneer walls are built without a space between the veneer and the substrate, so they don’t allow fast and complete drainage and drying behind the veneer. The traditional method of using two layers of building paper between the substrate and scratch coat may provide some drainage, but it doesn’t allow ventilation and it won’t prevent mortar bridging.
Since the characteristics of moisture movement in veneer walls are the same as those of masonry cavity walls, it only makes sense to provide the equivalent of a cavity behind the adhered veneer. Without this cavity, often called a “drainage/ventilation plane” in adhered masonry walls, mortar bridging between the veneer and substrate can occur, which can conduct infiltrating water from the veneer to the substrate. In addition, without a drainage/ventilation plane behind the veneer, there is no way for air to circulate and dry the veneer or the substrate. Veneers, mortar, cracks and flashing failures will allow moisture into the wall, and without a drainage/ventilation plane, it can damage moisture-sensitive wall components.
As a result, the need for efficient drainage and rapid, complete drying are important considerations when designing and installing adhered masonry veneers.
Moisture Intrusion Problems
When moisture can’t dry behind an adhered masonry wall system, the consequences range from merely inconvenient to very expensive, plus wall failure can seriously damage a builder’s reputation. They include:
- Mold growth
- Chronic efflorescence
- Excessive humidity
- Deteriorating fasteners
- Wall cracking and spalling
Let’s examine each of these potential problems in greater detail:
Mold growth – Insulation, sheathing, drywall and any wall materials with organic content are vulnerable to mold infestation resulting from moisture trapped in walls. Mold remediation is often an expensive and complicated process requiring professional expertise, and extensive mold infestations can lead to lawsuits that can damage a contractor’s reputation. Affected areas must be sealed off to minimize spore dispersion, and it is necessary to completely remove and replace affected wall components.
Chronic efflorescence – Efflorescence is the white powder that results from minerals in the mortar migrating to the exterior surface of the masonry veneer. Chronic efflorescence is caused by there being more moisture inside the wall than in the outside air. This causes the moisture to migrate through the mortar and results in a continuing cycle of mineral stains, surface cleansing and more mineral stains. While efflorescence doesn’t cause structural damage, it is unsightly, requires ongoing maintenance and will definitely create an unhappy customer.
Excessive humidity – Too much moisture in the air encourages bacterial growth, and relative humidity inside the walls of greater than 60% can feed mold growth, which may compromise interior air quality. When excess humidity infiltrates walls, interior humidity levels rise. This often increases the amount of heating and cooling required to maintain the comfort of occupants.
Deteriorating metal components – If the metal lath used for the scratch coat rusts, the rust will expand and may create cracks and even push the veneer off the wall. The metal fasteners used to adhere the masonry veneer to the structural substrate may also rust or corrode and eventually fail, and if the veneer pulls away from the substrate, it not only creates the opportunity for more water damage but can also injure people and damage property if it falls without warning.
Cracking and spalling – Excess moisture which migrates to the wall’s surface may lead to cracking and spalling, which can allow more moisture behind the wall, creating a vicious cycle of water damage leading to more water damage. Widespread deterioration may also have an adverse impact on leasing, and will almost certainly decrease a property’s value.
Unfortunately, moisture damage behind adhered masonry veneers may remain hidden for months or years before it becomes obvious, and by that time, repairs may be very expensive, sometimes reaching into the tens of thousands of dollars. Money spent on prevention of moisture problems will always be a good investment and is likely to pay for itself multiple times during the building’s life.
Of course, it is best to design moisture management into the wall to prevent damage rather than try to fix the wall once moisture has damaged it.. A properly designed wall will include:
Drainage/ventilation planes – A plastic mesh drainage/ventilation plane at least ¼” thick should be installed continuously behind the adhered veneer to allow drainage and airflow vital to managing moisture in the wall. The continuous mesh acts as a mortar break to prevent bridging, and moisture that does get behind the veneer travels to the bottom of the wall where it escapes through openings in the weep screed. The mesh also allows air circulation to promote rapid drying. Modern substrates are designed to withstand occasional wetting without damage, but if a substrate and other wall components never dry completely, mold and structural problems will result.
Weep screeds – Weep screeds are often used at the bottom of adhered masonry walls to provide a clean termination line for the veneer. While a weep screed has holes for drainage and ventilation, they are not considered to be weep holes as the term is used in masonry cavity walls. However, like weep holes, the weep screed holes provide a means for the moisture that flows down the drainage/ventilation plane to exit the wall and they provide a way for air to move into the drainage/ventilation plane to dry the wall components and the veneer from the back.
Moisture damage is the leading cause of masonry building failure – it can cost big dollars to fix and ruin a contractor’s reputation. Mortar Net Solutions is the industry leader in masonry moisture management, and DriPlane and LathNet are two solutions designed specifically to provide the drainage and ventilation plane vital to adhered masonry wall sustainability and beauty. Click here to find a distributor near you. Click here for free samples. For additional information, please contact us today!