Masonry Magazine June 1976 Page. 11
Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road, McLean, Virginia 22101
BRICK MASONRY WITH HIGH-BOND MORTAR
INTRODUCTION
The principal function of a masonry mortar is to bind structural units together and in so doing act as an adhesive and a sealant. For this reason, it is important to develop a mortar that will produce a complete, strong and durable bond with the masonry unit. It is true that masonry is affected by other properties of mortar, such as workability and strength. However, these properties are of secondary importance, except as they contribute to complete, strong and durable bond.
Historically, the mortar in brick masonry has been the weakest link in the system. This is not meant to indicate that brick masonry is weak, only that the mortar properties have been the governing factors. Conventional portland cement-lime mortar systems, however, when used in the proper proportions and with the proper aggregate, as outlined in Technical Notes 8 Series, produce excellent masonry that is strong, durable, watertight and has been widely used for decades.
For many years development work has been under way to produce mortars or mortar additives which will increase the mortar's bonding properties to structural clay masonry units. One such development currently on the market is Sarabond mortar additive, developed by The Dow Chemical Company. Sarabond is a liquid saran polymer additive which greatly enhances the bonding, compressive and tensile strength characteristics of the resultant mortar.
SARABOND BRAND MORTAR ADDITIVE
Over 20 years ago, The Dow Chemical Company began development of a liquid polymer known today as Sarabond. Originally developed for use in concrete bridge deck resurfacing and for chemical resistance, the polymer was tested with portland cement and found to have dramatic effects on the physical properties of mortar. Dow's research staff, in consultation with the Structural Clay Products Institute (now BIA), developed this additive to produce a mortar that would be strong enough to approach the brick strength and thus produce brick masonry more homogeneous in nature, rather than high strength clay masonry units held together by moderate strength mortar. It is not uncommon for Sarabond mortar cubes alone to show an 8000-psi compressive strength.
Most brick masonry design has been directed toward gravity structures which utilize the compressive strength of brick masonry. Sarabond brand mortar additive permits the designer to take advantage of the inherent tensile strength of the masonry units and utilize the Sarabond modified mortar's high tensile and bonding capacities-something not always available in conventional mortars. These features of brick masonry with high-bond mortar are especially helpful in the design of curtain walls and panels.
SELECTION OF MATERIALS
A most important aspect in the use of Sarabond additive is the selection of materials; e.g., brick, portland cement, sand and workability additive. These materials, as in conventional mortar used for engineered brick masonry, must meet certain minimum physical property requirements and be able to perform within the required stress ranges.
Selection of Brick. Certain physical properties and characteristics of the brick units may have considerable effect on their compatibility and performance when used with high-bond mortar containing Sarabond mortar additive. Additionally, the physical properties and characteristics of brick units will vary substantially from one type to another, and from one manufacturer to
FIG. 1