Masonry Magazine January 1968 Page. 36
Cold Weather Mortar Admixtures
(Continued from page 35) certainly this field has come a long way in just the past few years. Unfortunately, cold weather mortar techniques are not as well explored, and worse, most of the information developed about cold weather concrete does not apply directly to cold weather mortar construction. Much of it is worse than useless to the mortar contractor-attempting to transfer these techniques directly to mortar work will almost invariably mean poor results.
The reason for this lies in the difference in composition, and thus physical nature, between concrete and mortar, and it is important to understand and keep clear the distinctions between these two materials. So let's quickly review some basics:
Portland or Blast Furnace Slag Cement performs three major functions-creates the initial set and the compressive strength, and provides adhesion. The cement creates bond strength, and while some functions are similar in mortar and in concrete, there also are important differences:
* In concrete, cement acts as the whole medium of strength.
* In mortar, cement is but an element working with lime.
Today's mortars, generally classified as N, S, M or O types, are basically very similar in composition. The ingredients-cement, lime, sand-while the same, differ in proportions used in each of these mixes (Quality Proprietary mason's mortars omit the sand and use other selected admixtures, with proportions depending upon the particular manufacturer).
CEMENT requires moisture and favorable temperatures to reach maximum performance, developing most of its properties within days.
ABOUT THE AUTHOR
Daniel Guntin
Daniel A. Guntin is Marketing Manager for Sonneborn Building Products, Inc. in Des Plaines, Illinois.
Mr. Guntin has been in the construction industry for over fifteen years and prior to that served as an economic advisor to one of the larger manufacturers in the field. He has authored numerous articles for use in the construction industry with several appearing in the CSI SPECIFIER and CONCRETE CONSTRUCTION on leading industry matters. During the past year he served as one of the featured speakers on MCAA's All-Weather Conference which provided mason contractors with factual information in this vital field.
LIME is used to supply particular properties vital to mortar performance. Through its water retention qualities, it produces the workability characteristics of mortar, creating the retempering values common to lime mortars. In the hardened mortar state, lime provides elasticity values to mortar joints, and contributes significantly to control of shrinkage and cracking via its ability to heal cracks autogenously. In direct contrast to cement, lime is slow acting, requiring a much greater amount of time to convert to the hardened state. In fact, lime only begins to act when the mortar starts to dry out a direct contradiction to the requirements of cement for proper curing.
SAND is the inexpensive filler for the mix; properly graded, it favorably influences the workability of the mortar.
WATER is the catalyst that makes the process work, and it is a catalyst in the true sense of the word: it initiates and sustains the chemical reaction that results in hardened mortar with properties that can last for centuries.
The combination of these four elements under proper conditions leads to development of the hardened mass we know as mortar. This blend of elements differs from that hardened mass we know of as concrete, and consequently, we must ignore those factors that are critical only for concrete, and focus on those critical to the performance of mortar.
Some of these factors stem from composition, some from installation or usage factors. For example, concrete invariably is poured in fairly thick sections, and this sheer mass from both a design standpoint and as an in- (Continued on page 49)