Masonry Magazine April 1980 Page. 21
BIA Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road, McLean, Virginia 22102
11E
April/May
1973
INTRODUCTION
GUIDE SPECIFICATIONS FOR BRICK MASONRY
PART V OF V
MORTAR
This issue of Technical Notes is a continuation of Technical Notes 11 Series on "Guide Specifications for Brick Masonry" and contains the requirements for mortar for brick masonry. The Technical Notes will be equally appropriate for masonry constructed in accordance with traditional requirements or for engineered brick masonry.
The guide specifications in this Technical Notes are in CSI format and are based on the requirements of BIA M1-72 contained in Technical Notes 8A, "Standard Specification for Portland Cement-Lime Mortar for Brick Masonry". Mortar meeting the requirements of BIA M1-72 will meet all the requirements of ASTM C 270. A complete discussion of the qualities of good mortar is contained in Technical Notes 8 Revised.
GENERAL
Mortar requirements differ from concrete requirements, principally because the primary function of mortar is to bond masonry units into an integral element. For many years, portland cement, lime, sand and water have been the principal constituents of mortars. The most predictable mortars are still made with these ingredients.
"Standard Specification for Portland Cement-Lime Mortar for Brick Masonry", Technical Notes 8A, is the recommended standard for mortars to be used with brick masonry. It specifies materials, proportions and properties.
Properties of both plastic and hardened mortars are important. Plastic properties determine construction suitability; hardened properties determine performance of finished elements. No one combination of ingredients provides a mortar which is highest in all desirable properties. Factors that improve one property may do so at the expense of others. When selecting a mortar, evaluate all properties, then select the mortar providing the best compromise for the particular requirements.
Water Content. Water requirements of mortars are not similar to those for concrete. Use the maximum water compatible with workability and permit retempering.
Workability. No laboratory test exists for workability. Rely on water retentivity and aggregate gradation requirements to assure workability. To increase workability:
1. Use a well graded sand of which approximately 10 percent passes a No. 100 sieve.
2. Use highly plastic lime (Type S lime or lime putty).
3. Increase air content, but not to exceed 12 percent.
Flow and Water Retentivity. Flow is the percent increase in diameter of a test specimen, when it is placed on a flow table and then mechanically dropped 25 times in 15 sec. Flow after suction is determined by the same test performed on a specimen which has had some water removed. Water retentivity is the ratio of initial flow to flow after suction, expressed in percent. Construction mortars usually require greater flow and water retentivity than those for laboratory mortars. In general, to increase water retentivity:
1. Use a well graded sand.
2. Use highly plastic lime (Type S lime or lime putty).
3. Increase air content, but not to exceed 12 percent.
Bond. Bond is probably the most important single property of mortars. Currently the crossed-brick couplet assembly is used to test tensile bond strength (ASTM E 149). Many variables affect bond. In general, to increase tensile bond strength:
1. Mix mortar to the maximum flow compatible with workmanship. Use maximum mixing water and permit retempering.
2. Use brick whose suctions are less than 20 g when laid. Control high suction by wetting.
3. Use Type S mortar. (Increasing the cement content increases bond up to a cement:lime ratio of 1:2.)
4. Keep air content to a minimum.
5. Use mortars having high water retentivity.