Masonry Magazine July 1961 Page. 13
Lime in Masonry Mortar
(Continued from page 10)
Hundreds of years old masonry walls constructed with straight lime mortar without cement have not had moisture penetration. It should be remembered that through the years lime hydroxide converts back into carbonate, or limestone, and this action helps to seal up cracks which may develop during early curing of masonry. This action is known as "autogenous healing."
QUESTION "Is cement really necessary, or is it just a method of getting quick, high strength?"
ANSWER-The answer is "yes." Cement is required for both static and lateral stresses, due primarily to the fact that walls of modern buildings are thinner than those of older structures. Another reason is higher working stresses-and economy are effected by the use of cement in mortar. Still another reason is that of economy in time of construction by permitting loads to be imposed on masonry walls at a much earlier age when a lime-cement mortar, rather than a straight lime mortar, is used.
QUESTION "What is the effect of lime in grout?"
ANSWER-The building codes permit up to one-tenth part of the cement to be lime, for the purpose of holding the mass together and thus preventing segregation particularly where relatively coarse sand is used. Lime in grout has been found also to reduce shrinkage in the grout space where the spaces are more than 26" in width. When well-graded mortar sand is used, lime is not generally used in grout. Lime in grout is effective in hindering the rapid deletion of water in grout where used in conjunction with units having a high rate of absorption in excess of 0.025 ounces per square inch per minute.
QUESTION-"Can any other material be used with lime to increase mortar strength and decrease the amount of lime and still maintain durability?"
ANSWER-Authentic research over the recent past years indicates that strength and workability of mortar depend upon accepted proportions of Portland cement, lime, and sand. It has been found that maximum strength and bond between units, in flexure and diagonal tension or shear, has been obtained by using mortar composition of one part Portland cement, one-half part lime and four and one-half parts graded sand.
This mortar is generally used only in areas subject to high lateral force such as earthquakes and tornadoes.
Outside these areas a mortar containing one part Portland cement, one part lime, and six parts well-graded sand has been found to give adequate strength of masonry in the three respects previously mentioned.
Again, answering the question, no other materials have been found to equal the constituents and proportions mentioned.
QUESTION "What is the curve indicating the percentage of water tightness plotted against the percentage of lime content in masonry mortar?"
ANSWER Without considering strength, the curve representing sand without lime and sand with lime is a straight line in proportion to the amount of lime used up to a mix of about one part lime to five parts sand -the top of the curve being the maximum water tightness.
QUESTION "I have heard it said that lime in the mortar both improves and harms the water tightness characteristics of mortar. Which is right?"
ANSWER-The first statement is definitely right and the latter is definitely wrong.
QUESTION "Does lime cause efflorescence?"
ANSWER-The use of lime in mortar, according to Stanford Research Institute, does not measurably contribute to efflorescence. Neither do brick, sand or water. The major source of efflorescence, which invariably consists of water-soluble sulfate salts of sodium and potassium, is contained in cements. Witness old lime mortar buildings, many years old, which have shown us efflorescence except where continuous water leakage has occurred from downspouts, etc. Witness, too, severe conditions of efflorescence which frequently occur on buildings where no lime whatever is contained in the mortar.
As the result of research over the relatively recent past, the problem of efflorescence has pretty definitely been removed from lime's doorstep.
QUESTION-"When lime is used in mortar, is there a certain standard for cleaning walls?"
ANSWER-The first answer is that no standards have been set. One method of cleaning is to saturate the walls with water-then, working from the top down, scrub with a solution of one part muriatic acid to nine parts water. This should be followed immediately by rinsing the masonry with clear water. One objection to this procedure is that it may damage other materials or shrubbery. My company is presently engaged in laboratory and field research into acid cleaning, and it may be possible to expand upon this subject at a later date.
Masonry walls should be kept clean as they are constructed by bricklayers being careful and using only a bricklayer's stiff fiber brush and never (Continued on page 16)
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Other reinforcing may be heavier but, Grade for Grade and dollar for dollar, WAL-LOK puts more steel IN THE MORTAR where it counts 19.2% more than competitive products. SUPERSTANDARD Grade has 8 ga. Siderods rather than the 9 ga. used by others and it's the Siderods that end up in the mortar. Ladder type construction means no wasted steel to get in the way of insulation, pipe or conduit in the walls. No extra freight on steel that serves no useful purpose.
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1501 E. MICHIGAN ADRIAN, MICH.