Moisture management ranks as a top priority in a wall, and appropriate design and installation techniques will go a long way to eliminating the potential for health, legal, and financial devastation caused by excessive moisture in the building envelope.
While it is best to keep moisture from entering a wall in the first place, that is probably an unlikely occurrence. Modern designs are geared to thin wall construction and, to some extent, this allows buildings to leak. Besides precipitation, moisture can enter masonry walls from several different sources, including capillary action, water vapor, and groundwater. The objective is to control the water that enters a wall and provide a way for it to drain before it has a chance to do any damage or penetrate further.
The National Concrete Masonry Association maintains that successful moisture mitigation in concrete masonry walls involves several techniques, including flashing and counter flashing, weeps, vents, sealants, water repellents, post-applied surface treatments, vapor retarders, and crack control measures.
All components should have redundant use, with the preferred approach to controlling moisture being a four-level line of defense so that a wall’s water tightness will still be preserved if one of the systems fails. A proper line of defense includes:
- Surface protection
- Internal protection
- Drainage
- Drying
Detailing Techniques for 3 Common Masonry Scenarios
The following are three of the most common masonry scenarios
1) Full Bed Depth Veneers
In a cavity wall, moisture control relies on gravity and an unobstructed 2-inch airspace to get water down to the flashing and the weeps. This is the basic rainscreen principle wall.
2) Single Wythe Walls
A single wythe wall is a stone, brick, or concrete wall that is one masonry unit thick. Single wythe walls offer the economic advantage of serving as the structural system with multiple finish options on the exterior and the interior. Single wythe walls do not require the backup of a traditional cavity wall construction, but in order to provide full protection from the elements they must be carefully detailed and constructed.
3) Manufactured Stone Thin Veneer
An increasingly popular masonry solution is manufactured thin veneer, which refers to a lightweight, flat-backed, thin surface product that is applied directly to a solid facing. Thin veneers can either be directly adhered or attached to a mounting system.
WATER-REPELLENT ADMIXTURE ADVANCES IN BLOCK AND MORTAR
An effective method in controlling moisture in the building envelope is through water-repellent admixtures. Advances in technology have enabled manufacturers to offer water-repellent admixtures in both block and mortar. When used together, these offer superior moisture control and protection against all types of moisture infiltration.
Because untreated masonry units typically absorb water through capillary suction or wicking, the anti-wicking action of an integral water repellent will minimize the amount of water absorbed, and enable any water that has breached the surface to drain toward flashing and weep holes. No film forms on the surface of the masonry nor is the admixture impervious to moisture so the masonry remains breathable.
Historically, three types of admixtures have been used. Calcium stearate, tall oils and polymetric. Calcium stearate and tall oils have demonstrated an increase in air and a poor bond. Meanwhile, polymetric admixture has shown a better bond between units and mortar, though the air component has varied by manufacturer.
High air content in mortar lowers the compressive strength and can reduce the bond between units. Low air content will reduce the freeze-thaw resistance of mortar. Polymeric admixtures provide a denser, more uniform unit as well as moisture control and limited risk of efflorescence.
Especially effective in lightweight concrete masonry units and single wythe construction as added protection against water infiltration and wind-driven rain, an integrated water repellent agent assures design professionals that the product will be executed as specified and in the proper proportion for maximum protection.
While an integral water repellent in a masonry unit will go a long way to controlling moisture in a building, the joints are still susceptible to water infiltration. Use of both masonry units and mortar with an integral water repellent is necessary to provide full protection and ensure the surface is not breached by moisture in any form.
We’re Only Scratching the Surface
We’ve presented the potential problems with moisture in masonry, as well as an overview of the techniques to overcome them. For more in-depth information on moisture management in masonry, case studies and the latest products and solutions available, download our comprehensive Guide to Moisture Management in Masonry today.
