Masonry Magazine June 1993 Page. 22
Flashing
Coping
Interior
Interior
Drywall Concrete
Masonry
Surface
PVC
Tubing
Grout
Vapor
Barrier
Interior
Furring
Stud
Vent Vent
Surface Treatment
Wire Mesh
Cast-in-Place
Concrete Foundation
Drywall
Vapor
Barrier
Flashing
Concrete
Figure 4. Vents for Concrete Masonry Parapets
Figure 5. Walls with Interior Treatments
Flashings at Copings and Caps
During placement of the final courses of masonry in parapets, and commencing with the second course below the coping/cap location, wire mesh should be placed over cores so that grout can be placed for the positioning of anchor bolts (Figure 3).
In coping installations it is imperative that penetrations of through-the-wall flashing be tightly sealed to prevent water infiltration. A full mortar bed is required to be placed on the through-the-wall flashing to allow proper positioning of coping units. Full head joints are placed between the coping units. The joints between the coping units should then be raked and a joint sealant applied.
Coping units should be sized such that overhangs and a drip reveal occur on both sides of the wall. Metal caps require wood plates for anchorage. Anchor bolts provide attachment of the plates to the masonry wall. Soon after the cap is positioned, the wood plate will undergo a change, generally warping upward along its outer edges. The metal cap thus serves as a continuous vent; consequently, sealant should not be applied along its outer edges.
Positioning of Vents
Interior surfaces of concrete masonry parapets which are surface treated with materials that do not permit vapor transmission should be vented (Figure 4). Vents should be positioned in the course immediately below the through-the-wall flashing and enter the core area of the concrete masonry units. PVC tubing assemblies with elbows directed downward are effective in venting the wall, while preventing rain from entering the vent.
Interior Wall Treatments
Concrete masonry walls receiving an interior treatment provide an alternate method for the installation of flashings compared to that shown in Figure 1. In this condition, the flashing may be placed on the concrete foundation. The flashing should project through the wall and be carried up on the interior concrete masonry surface. Furring strips installed to receive the plastic vapor barrier and the interior drywall will hold the flashing in position. This procedure permits water penetrating to the interior surface of the concrete masonry wall to drain out at the base of the wall. Weepholes should project completely through the wall thickness. Vents should project into the core areas only. This procedure is recommended since vapor barrier backed gypsum board will not serve as an air seal. Joints between adjacent sections cannot be taped/sealed.
SUMMARY
Rain penetration may be the primary reason for moisture in walls, but interior humidity coupled with air movement and cold surfaces may also contribute to water problems. Water penetrating the exterior of a masonry wall must be directed outward by flashings to protect the wall and the contents within the building.
Flashings are essential at foundations, bond beams, above and below openings, and at copings. Weepholes and vents serve to reduce the moisture content of masonry walls. Proper selection of flashing materials, proper detailing, and proper installation will help ensure satisfactory performance.
*Replaces TEK 134, "Exterior Insulation of Block Walls," which has been discontinued.
NATIONAL CONCRETE MASONRY ASSOCIATION
2302 Horse Pen Road, Herndon, Virginia 22071-3406