Masonry Magazine July 1961 Page. 10
Lime in Masonry Mortar
The relationship of lime to watertightness, proper mixes and handling for maximum results.
In a question-answer period at a recent meeting of the Arizona Masonry Guilding, Inc., in Phoenix, Ariz., S. G. "Jack" Bishell of the Flintkote Co., had some interesting things to say about lime. Bishell is Southern Division Sales Manager, U. S. Lime Products Division.
Below are his remarks and answers to questions from mason contractors and architects attending the Guild meeting.
Lime is an essential ingredient of a good mortar. It is the oldest mortar material used continuously from the time of the erection of the Egyptian pyramids to the present. In fact, it was the only cementing agent available for mankind until the advent of Portland cement in the latter part of the 19th century. It provides to mortar workability, water retention, bond strength and elasticity.
QUESTION-"What does the lime content of mortar have to do with the difficulty of cleaning masonry walls?"
ANSWER-If walls are cleaned within a month or two after erection, the lime in the mortar will contribute to only a small portion of the cleaning problem. The most difficult stains are those caused by hydraulic cements. It should be remembered that it takes many months in the presence of moisture for lime to recarbonate into insoluble form. Even lime carbonate is easier to remove than hardened cement. Cements harden after about seven hours. Certain masonry or proprietory cements are of low strengths as exhibited in ASTM Specifications and these low-strength cements obvi ously can be cleaned off much more easily thah straight Portland cements.
QUESTION-"Are there any problems with lime in mortar that could affect various interior finishes where exposed masonry is scheduled-i.e.- various masonry paints, clear sealers, etc.?"
ANSWER-The first answer would be "yes" the reason being that if finishes are applied before mortar containing lime has hardened, the lime plus cement could burn through a finish. However, after the mortar has hardened, there should be no burning through provided the masonry has dried out.
Where it is desired to paint a wall before it has completely dried out, the only presently known covering is a first coat of a good water cement paint which is a "breather" type and will allow moisture to evaporate as a vapor. A second coat could consist of an acrylic resin or other breather type coating. Positive sealer types such as oil base paints should not be used on masonry of an age under several years except for parapets, planter boxes, etc.
These comments apply to any masonry with any type of mortar-with or without lime. Of extreme impor tance in connection with painting of masonry, or painting of anything for that matter, is the selection of top grade sealers and paints of the pr kind. As you all know, there a great many inferior and untested ings on the market today, and u them is asking for trouble.
QUESTION "How can we ge maximum from the lime we us mortar (workability, strength, tightness)?"
ANSWER- Maximum workal may be obtained by using Type hydrated lime which attains high ticity immediately. This shoule added to the mix as follows:
1-Approximately 80 per cent volume of water.
2-Total sand.
3-Total lime-mix for about minute.
4-Total cement mix for at five minutes.
5-Add balance of water to bri proper consistency-and con mix for at least another five utes. The mortar is "fatte as the mix continues.
Type "N"-normal hydrated require pre-soaking before being ed to the batch as does proce quicklime or pebble quicklime v require slaking into putty and a prior to using.
Maximum strength may be tained by proper proportioning mixing in the manner previously lined.
Water tightness is achieved by ing of mortar joints while the m is still sufficiently plastic to be pre against the unit edges before it stiffened.
It is important here to reme that to get the maximum of the desirable characteristics which lime imparts to mortar, one must use lime which has them to offer in the greatest degree. In other words, are limes and limes-some are si better than others. So far as the of Arizona is concerned, you are tunate in having available one o very finest Type "S" hydrated lin the entire country. This is Bo Canyon Miracle Lime a pressur drated dolomitic lime, manufac at Henderson, Nev. Although je ably proud of this product, we fra admit that its excellence essen goes back as the old miner sale "what God put in the hill." The s of our raw material is Sloan tain, near Las Vegas, where we c virtually inexhaustible deposit o ually pure dolomitic limestone. Sloan limestone, many million years old, is converted by me processes and controls into a revolutionary hydrated lime for struction.
QUESTION "What informati you have on lime against moi penetration thru the mortar joint
ANSWER-The best answer te is the exhibit of thousands of