Masonry Magazine August 1972 Page. 21
BIA Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road, Mclean, Virginia 22101
23A
INTRODUCTION
EFFLORESCENCE, PREVENTION AND CONTROL
An understanding of the nature and mechanisms of efflorescence, as well as the sources of soluble salts and of moisture in the assembly, is an essential requirement in an approach to the prevention of efflorescence. A detailed discussion of the mechanisms, the sources of salts, the sources of moisture and the nature of efflorescence are presented in Technical Notes 23, "Efflorescences - Causes", December 1969. This discussion is recommended reading prior to the use of this issue of Technical Notes, which presents recommendations for the prevention of efflorescence, analysis of efflorescence problems and removal of efflorescence.
PREVENTION OF EFFLORESCENCE
It is impracticable to attempt to preclude all soluble salts and all moisture from contact with the masonry assembly. However, the reduction of each of these dependent factors to a minimum is highly practical and will usually prevent the occurrence of efflorescence.
Selection of Materials
Selecting materials, facing brick, backup, trim and mortar for their minimum content of soluble salts and their maximum performance for a watertight structure is the first step in the prevention of efflorescence. In the following paragraphs recommendations are presented which should assist the designer in the selection of materials to preclude the occurrence of the efflorescence phenomena.
Brick Units. As stated in Technical Notes 23, brick units are available all over the United States which do not contain soluble salts or contribute to efflorescence. It is recommended that all facing brick be tested for efflorescence tendencies by the wick test contained in ASTM C 67, "Standard Methods of Sampling and Testing Brick". The wick test consists of partially immersing representative samples of brick in distilled water for a period of 7 days. At the end of this period the units are examined for efflorescence and compared to control samples that were not immersed. Brick should be rated at not more than "slightly effloresced" to be acceptable.
Backup. Many backup materials contain relatively high percentages of free alkali which may contribute to efflorescence on the face of a masonry wall. It is suggested, therefore, that back-up units be tested for their salts content by the wick test, as described by W. E. Brownell (Ref. 1).
When back-up materials which may contain soluble salts that would contribute to efflorescence are used, it is recommended that the wall details and design be such that the materials containing salts are separated from the facing brick, to avoid contamination which may lead to efflorescence. This can be done by using cavity walls.
Mortar. In Technical Notes 23, it is noted that the principal culprit for efflorescence contribution in most mortar mixes is the high free-alkali content of the portland cement. The tendencies of cement used in mortar to contribute to efflorescence may be predicted with reasonable accuracy from a chemical analysis of the cement. Cements high in alkaline content are more likely to produce efflorescence than cements of lower alkaline content.
ASTM Specifications C 358 and C 91, for slag cement and masonry cement, respectively, contain requirements for cement specified to be non-staining to limestone, i.e., "Non-staining cement shall contain not more than 0.03 per cent of water-soluble 'alkali"..."
This severe limitation on water-soluble alkali content can be met only by a few cements, other than portland blast-furnace slag cement and masonry cements made with slag cement.
ASTM Standard Specifications for Portland Cement, C.150, contain the following note as part of Section 4, Chemical Resistance: