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Products For Flashings, Accessories, And Reinforcing
1) Flashing For Masonry
2) Masonry Accessories
3) Reinforcing Steel In Masonry
4) Guide Specifications For Masonry Reinforcing
1. Flashing For Masonry
Flashing provides a degree of control over moisture penetration and movement within masonry. It is difficult to completely prevent rain water from entering at parapets, sills, projections, recesses, roof intersections, etc., unless proper flashing is installed. And without proper flashing, water which does penetrate a wall will not be diverted back to the exterior of the building. Flashings are usually formed from sheet metals, bituminous membranes, plastics, or a combination, the selection being largely determined by cost and suitability. Both installation and material costs vary widely. The differences in total costs reflect each and cannot be compared by comparing material costs alone. Because replacement costs can exceed the original costs, it is prudent to select a permanent flashing material for the original installation.
1.1. Copper. Copper is durable, is available in special preformed shapes, and is an excellent moisture barrier. It is, perhaps, more costly than most other flashing materials. Although exposed copper may tend to stain adjacent masonry, it is not materially affected by the caustic alkalies present in masonry mortars. It can safely be imbedded in fresh mortar and will not deteriorate in continuously saturated, hardened concrete, unless excessive chlorides are present. When using copper flashing, prohibit the use of chloride-base additives in mortar.
Combination flashing example foil sheet of 2, 3, 5, or 7 oz. copper is bonded to asphalt coated glass fabric with a ductile asphalt.
1.2. Zinc. Galvanized coatings are subject to corrosion in fresh mortar. Although the corrosive products apparently form a very compact film around zinc and apparently form a very good bond with the mortar, the extent of corrosion cannot be accurately predicted. Some zinc-alloy flashings are available. Like many alloys, these may have properties considerably different from those of the pure metal.
1.3. Aluminum. The caustic alkalies present in fresh, unhardened mortar will attack aluminum. Although dry, seasoned mortar will not affect aluminum, corrosion can again occur if the adjacent mortar becomes wet. Since the purpose of flashings is to direct the flow of water, it is apparent that uncoated aluminum will prove unsatisfactory as a flashing.
1.4. Lead. Lead, like aluminum, is susceptible to corrosion in fresh mortar. Furthermore, when lead is only partially embedded in mortar in the presence of moisture, it develops a differential electric potential, acting as the positive element of an electric cell. The resulting electrolytic action gradually disintegrates the embedded lead.
1.5. Plastics. As a group, plastics are becoming one of the most widely used flashing materials. The better plastic flashings are tough, resilient materials which are highly resistant to corrosion. However, because the chemical compositions of plastics are widely diversified, it is impossible to lump all plastic flashings into one generalized group. Some plastics will not withstand the corrosive effects of masonry mortars. Rely on performance records of the material, the reputation of its manufacturer and, where possible, test data to insure satisfactory performance.
1.6. Bituminous Flashing. Fabrics saturated with bitumen are used as damp checks and as low cost substitutes for metal flashings at the heads of openings at spandrels, and at window sills. If they are permanently insoluble in water and are installed with unbroken skins, they can be effective, although not as permanent as a good metal flashing.
1.7. Combination flashings. Often, materials are combined to utilize the better properties of each; e.g., sheet metal may be coated with plastic or bituminous materials. This particular combination can provide a lower cost flashing through reduction in metal gage or it may permit the use of corrodible metals which would otherwise prove unsatisfactory. It is beyond the scope of this bulletin to describe the numerous combination flashings available today.
1.8. Weep holes. All flashing must be drained to the outside. Tests at the National Bureau of Standards indicate that concealed flashings in tooled mortar joints are not self-draining without weep holes. Rather, they serve as a trap to collect moisture. Every 24 inches, provide weep holes in head joints immediately above all flashing; keep weep holes free of mortar droppings. When wicks of 1/4-in. Fiberglass rope or similar materials are used to prevent staining, weep holes should be spaced every 16 inches.
2. Masonry Accessories
Ladder type reinforcement with adjustable ties.
Adjustable veneer anchor for seismic zone 2 use.
Control joint for CMU walls.
Masonry accessories continued on next page...
The NW Masonry Guide Table of Contents
Masonry Institute of Washington
Washington State Conference of Mason Contractors
