Masonry Magazine June 1964 Page. 12
Problems In Specifying Mortars
claim their products can be used universally without regard to absorption characteristics and surface texture of masonry units, weather, or other exposure conditions. Their only recommended variation in proportions and ingredients is that necessary to achieve higher compressive strengths under unusual loading conditions. Manufacturers of other mortar materials recommend that proportions and ingredients be varied to suit the masonry units to be used and the exposure to which the masonry is to be subjected. This is certainly in the nature of a contradiction in the specification writer's mind.
Some manufacturers base their statements, with respect to mortar quality, on compressive strengths and autoclave expansion. Others claim strength is relatively unimportant and that an autoclave test has little significance in the actual performance of a mortar in a masonry structure. Some manufacturers claim superiority because of the introduction of water-repellents. Others claim that the use of such ingredients has little permanent effect.
Don't you think we need some clarification and some meeting of minds to eliminate the mysteries surrounding mortar materials and mortar mixes? What are some of the items relating to mortars on which we need more clarification and definite information? To approach these questions in an orderly manner I have organized subjects under five major categories: Masonry Mortar Properties, Mortar Selection, Workmanship and Job Control, Design Details, and General as follows:
1. Masonry Mortar Properties
Aggregates
Mortar Bond as affected by:
Water retention
Mortar flow or consistency
Air Content
Retempering
Brick suction
Type of Mortar
Ingredient Proportions
Joint thickness
Construction weather
Workmanship
Relation between masonry unit characteristics and mortars
Durability (weather effects)
Autoclave expansion
Color and discoloration factors
Efflorescence
Leakage factors
Strengths
Extensibility (flexibility)
Admixtures
Wetting of brick
Reconstitution of bond
2. Mortar Selection
For various exposures
Proprietary masonry cement mortars vs. cement-lime mortars
3. Workmanship and Job Control
Storage and handling of materials
Measurement batching and mixing of mortar ingredients
Wetting of masonry units
Parging (back-up and below grade)
Bonding and reinforcing
Protection during construction
Heating during cold weather construction
Cleaning
4. Design Details
Bonding of facing to back-up
Position of parge coat
Waterproofing coatings
5. General
Let us examine some of these items in greater detail, and particularly in the light of providing for the specifications writer data on each item in terms that are readily usable, and, hopefully, that might be incorporated directly into a specification.
1. Masonry Mortar Properties
Aggregates. Some authorities suggest that proportions be adjusted to compensate for gradation deficiencies. How is this done? What ingredient quantity is to be adjusted and how do such adjustments affect the overall mortar properties bond, permeability, durability?
Mortar Bond as affected by:
Percent of water retention in various mortars. What is really meant by this? Is a high percentage of water retention good in all mortars? If not, when is it good and when is it detrimental? Is water retention related to the initial mix and placing of the masonry, or the result of wetting after the mortar has set up?
Initial flow or mortar consistency. Tests for water-retentivity require an initial flow of 105 to 115 percent. But this does not describe the consistency of mortar as it should be used on the job. What is the optimum initial flow, and how can it be determined on the job site that a mortar has the initial flow necessary to achieve maximum bond? Is a slump test, similar to that used for determining consistency of concrete, of equal or sufficient value in establishing mortar consistency?
Air content. Proprietary masonry cement mortars have air contents ranging from 15 to 30 percent. Cement-lime mortars range from 10 to 15 percent or more depending upon whether or not an air-entraining agent is used. ASTM Specifications call for a minimum of 12 percent for masonry cements, without a maximum. What is an optimum air content? Should air-entraining agents be used at all in cement-lime mortars?
Retempering. What is meant by this term and what does such a procedure do for mortar?
Brick suction. Just how much does brick suction or the loss of moisture in the mortar mix to the brick or other masonry unit affect the mortar bond, adhesion, shrinkage cracking, etc.? Is the addition of lime in portland cement mortar the complete answer, or are other factors involved?