Lime has been used for mortar for thousands of years. You'd think by now a more modern material would have emerged. But most masons still prefer portland cement-lime mortar. There are some alternatives, though, which their proponents insist can provide a mortar with superior characteristics. Masonry Construction offers two reports that let both sides have their say.
According to Margaret Thomson of Chemical Lime Co., saying it replaces lime doesn't make it lime. Charles D. Meadowcroft of Peninsula Products Inc. contends that lime alternates are not and do not want to be lime.
While the standard used to specify mortar in the United States provides clear benchmarks for quality, it does not provide for the replacement of any of the constituent materials and clearly states that the use of admixtures is not permitted unless specified.
Each of the materials used in an ASTM C 270 mortar has its own set of standards to assure the quality of the mortar. Quality control must begin at the quarry and continue throughout the production process. Lime producers certify that they meet these requirements.
Products marketed as lime-replacement additives fall into two categories: combinations of bentonite clay with diatomaceous earth and cellulose or petroleum byproducts. Neither product is chemically or physically similar to lime. Although marketed as lime replacements, these materials could be more appropriately considered cement replacements, as are all pozzolans.
Whether at a blending plant or in the field, the mix requires adequate dispersion, usually by increasing the mixing time.
The producer of the lime-replacement additive has no ASTM standards to meet.
Chemical Lime Co., compared cement-lime and lime-replacement mortars: water retention and air content of the plastic mortar, compressive strength of the hardened mortar, and flexural bond strength and water penetration of brick masonry made with each mortar. The potential for increased efflorescence was also investigated. Although there is no test available for efflorescence, chemical analysis of the alkali level of the cement, limes, and lime-replacement additives was conducted.
All of the mortars were mixed following the procedures of ASTM C 270, not those of the manufacturers.
The water retention values for all of the lime-replacement mortars were lower than required, and the air content was well in excess of the maximum required. Mortar made with the lime-replacement products did not pass the requirements of ASTM C 270, and therefore, cannot be specified under this standard.
The compressive strength of the lime-replacement mortars was less than that of the cement-lime mortars although both had compressive strengths in excess of the 1800-psi minimum required by ASTM C 270's property specification.
The flexural bond strength of the cement-lime mortars was 50% greater than that of the lime-replacement mortars. The water penetration testing showed that the lime-replacement mortars allowed four times as much water or more to penetrate the wall as did the cement-lime mortar.
The lime-replacement products have significantly higher alkali contents than lime and will, therefore, increase the total alkali in the mix.
Conclusion: With the exception of compressive strength, lime-replacement mortars did not meet the requirements of cement-lime mortars as defined by ASTM C 270, nor were they equivalent in flexural bond strength or water-penetration resistance. Where hydrated lime acts to dilute the alkali in a cement-lime mortar, the lime-replacement products contribute to the total alkali content of the mix. The comparative data indicate that mortars made with products marketed as lime replacements may have some level of workability but do not provide performance in the important areas of masonry structure (flexural and compressive strength), water penetration, and aesthetics (efflorescence).
Suggesting that these materials are equivalent to cement-lime mortars as defined by ASTM C 270 seriously undermines the intent and assurance provided by that standard. If a product is to be a replacement, it should perform equal to or better than what it is replacing. To date, nothing surpasses the performance of lime in masonry mortar.
Charles D. Meadowcroft
At the outset, it should be made quite clear that all the test results are based on the premise that "all of the mortars were mixed following the procedures of ASTM C 270, not those of the manufacturers." In attempting to determine whether a proprietary material is able to produce certain properties, is it not logical to follow the manufacturer's mixing procedures?
Neither a bentonite-based lime alternate nor a sodium bentonite-based alternate to lime is chemically or physically similar to lime.
ASTM Standard Specification C 270 is a document developed to set precise tests, procedures, and requirements for mortars made with standard materials (such as portland cement, lime, and sand) that each must meet its appropriate ASTM standard. ASTM does not name proprietary products in their specifications.
Fortunately, there are two other ways for proprietary products to gain approval for use in construction. One way is to create a generic name for the product and get a standard written for that product, as is true for masonry cement and mortar cement. The other is through the evaluation services of each of the three model code groups (ICBO Evaluation Service Inc., SBCCI-Public Safety and Evaluation Service Inc., and BOCA Evaluation Services Inc.). Contrary to what Ms. Thomson states, these tests are made available to users by the manufacturer.
Producers of lime alternates have to meet the most important standard of all: the performance standard. These requirements include flexural bond and compressive strength, drying shrinkage, water retention, corrosion resistance, freeze-thaw durability, sulfate resistance, and autoclave expansion. Using these performance standards, access is granted to products that might actually improve performance and open up the marketplace to more healthy competition.
Testing of Easy SpredTM, the lime alternate manufactured by my company shows evidence that this lime-alternate mortar easily meets the requirements for flexural bond strength and drying shrinkage, and compares favorably to portland cement-lime mortar for water penetration.
Efflorescence tests performed on face brick showed no efflorescence. Other mortar solution tests showed slight to no efflorescence. In June 1989, the National Concrete Masonry Association's Research and Development Laboratory issued a report titled "Concrete Masonry Wall and Assemblage Tests Constructed with Easy SpredTM Mortar." It concluded that "all tests showed a favorable comparison with respect to mortar strength, mortar plastic characteristics, and mortar behavior in assemblage. It can be concluded that Easy SpredTM can substitute for hydrated lime in masonry mortar and it will behave in a similar manner. The user of Easy SpredTM should follow very strictly the manufacturer's instructions."
Portland cement-lime alternate mortar has been used successfully on thousands of projects in all seismic zones on all types of masonry construction. Many of these projects used the portland cement-lime alternate mortar because the builder and end user wanted to ensure that the structural integrity, aesthetics, and favorable water penetration characteristics described by Ms. Thomson were achieved, especially in adverse weather conditions.
Portland cement-lime alternate mortars compare favorably to portland cement-lime mortars when manufacturer'