Masonry Magazine June 1964 Page. 15
Problems In Specifying Mortars
Type of Mortar. Is there an established relationship of mortar type to type of masonry unit used, particularly with respect to bonding of mortar to the unit? What are the relative merits of straight portland cement mortar, masonry cements in which pulverized limestone has been added, high-lime mortars, and straight lime mortars? With so many varieties, each with its particular claims, it is readily apparent how difficult is the choice.
Ingredient proportions. As we study recommended proportions of ingredients for the various mixes it is most difficult for the specifications writer to keep all of these combinations constantly in mind. As you must realize, "Masonry and Mortars" is only one of many sections in a specification with which the specifications writer must be familiar. He is unable to maintain the continued and close familiarity with this subject enjoyed by the specialists dealing daily with cement mortars. It would be of greatest help to have available a ready reference listing all of the various mixes, the proportions of all ingredients in each mix, and the particular advantage of each combination.
Joint sizes. Does the size of the mortar joint have any purpose other than esthetics? For instance, architects generally prefer narrow joints; does that affect the strength of the wall, leakage, etc.? What is the best joint, if any, to reduce or eliminate leakage in walls?
Construction weather. This is an area generally left to chance in the average specification, other than to limit the placing of masonry in freezing weather without special arrangements for continuation of the work. To what extent are mortar mixes affected by weather? What adjustments should be made for hot, dry weather, and freezing conditions? Does fast drying of mortar affect its set, strength, bond and similar characteristics? Does freezing of mortar adversely affect its set and durability?
Workmanship. Mortars can affect workmanship more than is readily apparent. All mortars should possess sufficient workability to provide ease of spreading and well filled joints without segregation. Mortars should produce intimate, complete and durable bond with the units, set up reasonably early to permit proper tooling and otherwise fulfill its intended purpose. This phase of use of the material should be borne in mind when discussing many of the other aspects previously mentioned.
Relation between masonry units and mortar proportioning. How does surface texture at mortar interfaces and of exposed surfaces affect mortar proportioning? What are the effects of rate of suction, capillarity, capillary rise, porosity and permeability of masonry units on the function of mortars and wall integrity?
Durability (weather effects). Just what is to be expected as to the effects of weathering on all types of mortars: portland cement, lime mortars, and others? We want to know what effect the two extremes of weather-hot and cold, dry or wet-have during the laying and curing period. We are interested also in the effect of quick changes from hot to cold weather that so often happen in the Washington, D. C., area. The effect on mortars of climate, such as the cold of Alaska, or, at the other extreme, the hot, humid conditions of the South Pacific, is of importance to us. As you realize, American construction projects now are located throughout the whole world. But the specifications are written in this country.
Autoclave expansion tests. What is the value of such a test on the cementitious ingredients of mortars? ASTM: C151, "Test for Autoclave Expansion of Portland Cement," describes the method involved. It is applicable, evidently, only to portland cement and masonry cement essentially compounded with portland cement. Obviously, the test could not be applied to lime, and it is questionable whether it is applicable to masonry cements whose ingredients include a fairly large proportion of lime, or to mixtures of portland cement and lime. Since it applies only to portland cement and to certain types of masonry cements, what is the test's value in the comparison of various types of mortars?
Color and discoloration factors. What are the most accepted types of materials for coloring mortars and for non-fading permanent coloring? Which colors are most subject to change from action of the weather or other elements? Do color admixes affect the strength of the mortar? How do we obtain a uniform color in mortar between different laying periods? Also, an explanation of the reasons some mortars dry in patchy color is needed.
Efflorescent factors. Just what is efflorescence? What are its causes? How can it be avoided? How can it be eliminated, once started? Is there a reasonably simple, quick, most effective test to guard against efflorescence that can be specified? This may appear to be self-explanatory, but actually it needs much study.
Leakproof factors. We are aware that this condition depends primarily on the application of mortar. However, we feel that more studies on consistency of mortar, workability, adhesiveness, etc., are needed so as to minimize failure. Are leaky walls due to poor mortar and mortar materials, or poor workmanship, or a combination of these? Or is it a matter of high strength mortars against lower strength and more absorptive mortars? How important is measuring and mixing of materials in producing good workable mortar and leak-free walls? Why do so many mortars, even with high portland cement ratio, cure out sandy and rapidly weather-out of the joints? Just how vital is furrowing the bed in avoiding leakage? A great deal apparently can be covered in this subject including parapets and other walls exposed to weather on both sides, and walls subject to superimposed loading functioning under various weather conditions.
Information on strength tests. Compression, tension, shear-just what do they mean? Do we mean that the mortar is related to the same respective factors in the masonry units, or do we mean performance in connection with the masonry units only? Should the mortar have greater strength than masonry units in all of these categories-compression, tension and shear? Do these factors have a direct bearing on some of the aforementioned items-leakage, color, efflorescence, water retainage, etc.?
Extensibility. Just how valuable is the characteristic of mortar and how does extensibility vary with ingredients and their proportions?
Admixtures. In addition to the effects of water-repellents and air-entraining agents, what can be expected from the use of cement-dispersing agents and of accelerators, such as calcium chloride? What effect do bacteria repellent admixes have on mortars, if any?