The Important Issues with Masonry Barrier Systems Words: Steven JuddPhotos: Steven JuddA barrier is an element, device, or material that is intended to stop something from passing through. Road barriers stop traffic, for instance. Sun lotion with a high SPF rating will stop UV rays (for a limited time) from damaging the skin. In masonry, barriers can be good things or bad things. There are many kinds of barriers that relate to masonry in general and exterior building enclosures in general. There are water barriers, vapor barriers, and air barriers, to name a few. They all do different things and are used for different purposes, some fairly technical.Air and vapor barriers serve critical functions in an exterior wall design. They allow moisture to evacuate from a wall assembly in the correct direction, either inward or outward, depending on the climate and the season, and to avoid trapping moisture in the wall. Too many barriers are not necessarily a good thing, however. These air and vapor barriers are generally designed, specified, and detailed by the design consultants and do not typically impact the scope of work of a mason. Water barriers, on the other hand, are often the responsibility of the mason. It would be good to know which kind of barrier might be exposed while installing masonry material, and avoid creating breaches in that barrier during masonry installation. Patch holes, rips, or tears as specified, should they occur.Air passes through gaps, holes, openings, and seams in air barriers. Vapor migrates or diffuses through materials at the microscopic level. Obviously, a hole in a barrier will allow both air and vapor to pass through. Air leakage through a hole in an air barrier can move 100 times more moisture than via vapor diffusion through a material.There is another word that gets misused or misapplied, at times, when it comes to masonry, and that word is “sealants.” Sealants, in terms of joint treatments, are necessary things to prevent water and debris (and other little creepy things) from penetrating an otherwise open joint, like an expansion joint in brickwork, or a control joint in concrete work, or a seismic joint that allows building segments to move independently. Joints between adjacent materials, like around windows and doors, should also, most likely, have a sealant joint.“Sealants,” in terms of surface coatings on masonry walls, need to be carefully clarified and understood. A surface treatment sealant can be a barrier in the wrong way.Some masonry materials can be porous, such as limestones, sandstones, and plain/normal CMU, which allows water migration through the exterior surface. Travertine can have actual holes, unless they have been filled (“filled travertine”) with a cementitious mortar, grout, or an epoxy mortar. Other masonry materials like glass block, which has zero water permeability, and some brick units with very low absorption, and some stones (granite, basalt, slate) are very effective water barriers. However, water can still pass through walls built with impermeable masonry units via the mortar joints. Mortar joints may not be properly filled, may have breaches, open spots, or “B” holes, and may have cracks due to wall movements. These phenomena allow a path for water to enter the wall.Cavity wall construction (or anchored veneer systems) is one of the best water management systems available and is considered a “rainscreen” by the Rainscreen Association in North America (RAiNA). Rainscreens first became popular in Western Europe and other areas. These systems use the exterior surface of the cladding material as the primary water barrier, backed by an air gap providing a capillary break, which is then backed up by another water barrier wall with waterproofing or water-resistant barriers. Some of these systems are even designed with open joints. These systems do not need any surface treatments (film-forming surface treatments) on the cladding to enhance the performance of the overall system.Single wythe masonry walls tend to be the biggest challenge with water infiltration and have the greatest need for the right kind of barriers.We all know “regular” CMU can be very porous, so the first step to control water infiltration is to add an “Integral Water Repellent” (IWR), one or more “hydrophobic” (water-hating) chemicals, to the dry (or wet) concrete mix at the point of manufacturing. These chemicals act to repel water throughout the matrix. The IWR acts to repel liquid water but allows water vapor to pass through, which is critical to long-term wall performance. IWR is a “long-term to permanent” solution. The material is not exposed on the surface to be degraded by UV, abrasion, cleaning, or abuse. In some extreme situations where water is nearly always present (think about a tunnel car wash), a topical breathable water repellent can also be applied. It is best not to use an impermeable, film-forming surface coating.Most fired clay structural masonry units (“hollow clay units” per ASTM C652) have lower absorptions than most CMU and so can be sufficient unto themselves for most applications as an effective primary water barrier. As with CMU, extremely wet environments may warrant the application of a topical breathable water repellent.Regardless of the masonry material (CMU, stone, or brick), single wythe walls have mortar joints that can be the weak link for water infiltration. It is common for IWR admixtures to be added to mortar for assemblies with IWR-modified CMU. IWR added to the mortar generally changes the “feel” of the mortar; it does not “suck” or hold the masonry units as easily. This is something that can be dealt with by the mason, with some experience or practice. CMHA promotes the use of IWR admixtures in mortar when used with IWR-modified CMU. The Brick Industry Association (BIA) officially does not recommend the use of IWR admixtures in mortar for brickwork, as doing so negatively affects the bond between the brick units and the mortar.Without IWR in mortar, the best way to reduce water infiltration is to use a breathable water repellent surface treatment that will not only treat the masonry units but will also treat the mortar as well. Think about a typical brick masonry wall with modular-sized brick; roughly 19% of the surface area of the wall is mortar.Topical breathable water repellents (often incorrectly called “sealers”) generally have limited penetration into the masonry unit surface and can degrade over time. These treatments are not a permanent solution and must be reapplied to maintain their performance at intervals ranging from 5 to 25 years, depending on the concentration of the chemicals and the type of chemicals used. The most common hydrophobic chemicals used are silanes and siloxanes. These chemicals are silicon-based, not silicone-based. Silicon is a chemical element. Silicone is a chemical compound that has silicon as one of its ingredients.Silanes and siloxanes will not bridge cracks or gaps. Those cracks or gaps will remain pathways for water infiltration, so they should be repaired. Silanes and siloxanes work best in small/tiny pores and micro-fissures measured in microns, up to about 1/10th of a millimeter (0.1 mm), or roughly 1/256 inch; very small. They repel water by not allowing the surface tension inherent in water to be drawn into small pores and cracks via capillary action. They do not create a physical film. It is critical for the long-term performance of the masonry assemblage to allow it to breathe and allow any infiltrating water to evaporate and escape from the wall so the wall can dry out. Films and true impermeable surface sealants can trap water in the wall and create expansive freezing lenses of water in cold weather that can spall the face of the masonry.It may not “B” possible to prevent all penetrations and cracks from being present, so a drainage and weep system becomes a critical element of single-wythe structural masonry walls. Solid grouted walls may still have “inherent voids” which can provide “channels” to control water, depending on the type of masonry units being used, such as head joints, for instance. Partially grouted walls or walls without any fill can easily be drained via several different weep systems, each with pros and cons. Examples are pan flashing, membrane flashing, and mesh channel systems. Designers should take care to consider the paths that water can take, getting past the primary barrier surface, and provide systems to capture and channel water back out to the surface of the building. Weeps immediately above horizontal bond beams in partially grouted walls are one such location.Masonry walls are generally chosen for their beauty, low maintenance, and permanence. Any applications considered for use that will alter the performance of the walls, such as water repellants, used to reduce water infiltration or reduce water penetration, should always be evaluated for the performance enhancements they can offer, while also investigating any negative impacts that the material may have on the masonry. Some applications are touted as not changing the appearance of the masonry, but they often do, to some degree or another. Test all applications in an inconspicuous location or on the mock-up, prior to mass applications on the walls. And most importantly, enjoy building a lasting addition to the built environment by using masonry that will last for generations.About: Technical Talks
