Masonry Cement vs Portland/Lime Blends
There is much confusion between masonry cements and portland/lime blends in the masonry market today. The one question that is always asked is, “Which one is better?” The only way to answer that is, the products are different but when handled appropriately produce quality masonry construction. Masonry cements and portland/lime blends have different ingredients, manufacture processes, and are covered under different specifications. However, the two have similarities which include: bond, workability, weather resistance, water permeance, efflorescence potential, water retention, and board life.
Masonry cements are manufactured in a cement plant using portland clinker, plasticizers, and an air entraining agent all interground together. Some items which can be used as plasticizers are limestone, clay, raw feed, and lime hydrate. These materials when finely ground have the ability to adsorb water thus increasing workability. Air-entraining agents protect from freeze-thaw deterioration and provide additional workability. Air entraining agents produce tiny, microscopic air bubbles in mortar. These air bubbles act as ball bearings, increasing workability. The freeze-thaw protection is accomplished because any water that may freeze and expand will do so inside these bubbles, therefore not allowing stresses to build within the mortar joint.
Masonry cements in Types N, S, and M are covered by ASTM C91, Standard Specification for Masonry Cements. All manufactures of masonry cements must show that their product meets the physical requirements set forth in ASTM C91. ASTM C270, Standard Specification for Mortar for Unit Masonry, covers construction of masonry structures using mortars. Therefore, construction of masonry structures using mortar in accordance with ASTM C270, and masonry cement qualifying under ASTM C91, renders acceptable mortar provided you have quality workmanship.
Portland/lime blends are manufactured in a blending facility using portland cement and hydrated Type S lime. The lime provides for workability, much the same as plasticizers do for masonry cements. Lime is made up of hexagonal shaped hydroxide crystals. These crystals are thin, flat particles which slip and slide over one another, but never separate completely, acting as a lubricant. The particles of lime in a portland/lime blend are very fine, helping to increase its ability to retain water effectively, again to help with workability.
Portland/lime blends in Types N, S, and M are covered by ASTM C270 only. This is due to the fact that the two ingredients in a P/L blend, portland cement and lime, are each covered by their respective specifications: ASTM C150, Standard Specification for Portland Cement, and ASTM C207, Standard Specification for Hydrated Lime for Masonry Purposes. Therefore, construction of masonry structures using mortar in accordance with ASTM C270, and a P/L blend using ASTM C150 portland cement and ASTM C207 lime, renders acceptable mortar provided you have quality workmanship.
Despite the differences between masonry cements and P/L blends, they still are very similar materials where end results are concerned. One of the most important items when constructing a masonry wall is to insure its ability to keep the water out, often referred to as water permeance. Both masonry cement mortars and P/L blend mortars have the capability of providing for water permeance, given they are used effectively by the mason. The key to water permeance is full, complete bed and head joints. It is common for a mason who is comfortable using one of the products, to have problems using the other. The most common reason for a wall to lack water permeance is the mason was not familiar with the product being used and thus was unable to get full, complete head and bed joints. Another item which follows into this same idea is bond. Full head and bed joints provide for a stronger more complete bond, which is achieved by a mason who is familiar with the product they are using and knows how to use it effectively.
May times, those opposed to masonry cements contend that the air bubbles in the mortar interfere with bonding and thus water permeance. Studies have been preformed to test bond with different cements, but many of these tests are preformed in “stored-in-air” conditions, which do not readily compare to real life situations. Tests preformed in a way that resembles actual field conditions show that masonry cements achieve high bond strengths, just like P/L blends do. This is due to the fact that all cement based products need water to hydrate all of the cement particles. When a specimen is stored in a laboratory without atmospheric moisture, the cement particles are not allowed to hydrate completely, decreasing bond and water permeance capabilities.
Another issue commonly misunderstood is efflorescence. Efflorescence is the white colored “stain” which can appear on masonry construction. Many people confuse this white colored stain for lime and blame the P/L blend. However, this “stain” occurs when water dissolves the soluble salts contained in all masonry materials, the water then evaporates, and the salts are left behind. This occurrence is common on newly constructed masonry structures, due to the inherent moisture trapped within the structure itself. Given time, it fades and does not reoccur unless moisture is introduced somewhere else in the system.
One last issue that comes up when talking about masonry cements versus P/L blends is the potential for autogenous healing of fissures in mortars when a P/L blend is used. The theory is that when a fissure develops in a P/L mortar, the lime in the mortar is capable of filling in the fissure. It is important to point out that it is the tiny micro-fissures that can be healed, not cracks. This happens because water is allowed to enter through the fissure, which dissolves some of the calcium in the lime rich mortar. Then carbon dioxide from the air reacts with the dissolved calcium producing calcium carbonate, which plugs the fissure. There is no doubt that this can occur, the only question is what happens to the void that is created when the calcium dissolves and moves to fill the fissure. One final thing, autogenous healing will not remedy cracks and other problems usually contributed to poor masonry techniques.
The controversy surrounding masonry cements and P/L blends will more than likely never go away. Just remember, the key to having a successful masonry project, is a well qualified mason on the job who is comfortable with the product he is using, not which type of mortar the designer specifies for the project.
Guide To Masonry Mortar
Types Of Mortar ( ASTM C-270)
Fire walls prohibit the spread of fire from one compartment of building to another for the time it takes the fire to burn itself out. The purpose is to prevent major property loss, a level of performance which also provides a significantly higher contribution to life safety than fire separation walls. Concrete masonry, due to its inherent qualities of durability, reliability and superior fire resistance characteristics, is considered by most to be far superior to other types of non-combustible materials and is well suited to fire wall construction. A fire wall must restrict the spread of fire and extend continuously from the foundation to or through the roof and have sufficient structural ability under fire conditions to allow collapse of construction on either side without collapse of the wall.
Concrete masonry products are often used in fire walls because it doesn’t burn, melt, twist or warp when exposed to fire. If a stud wall endures a fire, chances are good that it will be damaged beyond repair, not to mention the damage that the piece of sheetrock will sustain when blasted with a fireman’s hose. Block walls, on the other hand, can be simply cleaned and/or repainted.
Some believe that having a sprinkler system will replace the need for good fire resistant masonry walls. This isn’t the case. Although sprinkler systems may reduce the amount of damage in a building during a fire, they do not prevent them or even stop them. At best, they reduce the rate at which a fire spreads. Sprinkler systems are best used only as backup measures.
The dimensions of your masonry unit will help create the impression you wish to make with your project. Create height or width, strength or warmth, using relative thickness and length, as well as absolute size. Each market has its favored residential size, but may sizes are available for residential and commercial use. Utility size brick (11 5/8″ x 3 5/8″ x 3 5/8″) are frequently used on large institutional projects. Closure, or econo size brick (7 5/8″ x 3 5/8″ x 3 5/8″) are an option to utilities, giving a different dimensional aesthetic. More traditional appeal is acheived with small, residential-style units. The most common unit in the Central Virginia market is engineer modular, known as oversize (7-5/8″ x 2-5/8″ x 3 5/8″).
Enduring, Maintenance-Free Finish
While a number of exterior finishes may look fabulous on grand opening day, many age badly and quickly. At best, their appeal can be extended with regular reapplication and/or cleaning, erasing the installation cost savings that made them attractive options in the first place, and creating an annuity for a maintenance provider. Masonry does not look dated or dog-eared after ten years, but instead looks great after twenty, or fifty, or hundred. It fequently looks better over time. With no painting. With no washing. Still standing and looking beautiful long after its alternative has passed through its dated embarrassment phase, through its eyesore phase, and into its demolition and replacement phase.
Safety/Security of Masonry Products
With recent concerns regarding safety from life threatening acts such as bombings, biological weaponry and random shootings, many Contractors are opting to use building products that offer the best protection. This effort toward the highest security and durability is especially sought after in buildings used as government offices, schools and correctional facilities. Designers of such buildings as the Pentagon in Washington, D.C. have opted to use masonry products to provide the maximum security for both the human lives as well as the important records housed inside the structure.
In the case of a bombing or fire, masonry plays an integral part in securing a building. Masonry walls can be used to compartmentalize a structure for the containment of fires. Masonry can also be used to structurally stabilize as well as defer much of the weight load in the event of a blast that causes the loss of a column. Masonry, in turn helps to prevent progressive collapse of the structure.
Under test conditions, walls made using 8-inch solid or solidly grouted concrete masonry units as well as those made of 12-inch hollow concrete masonry units with sand-filled cores both deterred bullets from high-powered rifles, revolvers and machine guns from passing through them. In the case where natural light is preferred, bullet-resistant glass block can be used effectively for security without creating the look and feel of a bunker.
Because concrete block and brick are very durable and can take all kinds of abuse it is often used in schools, correctional facilities.
A key element in the heating and cooling of any structure is the relative tendency of its skin to resist heat flow. An exterior resistant to heat transfer effectively provides a layer of insulation which more heat conductive materials do not. Masonry walls have a more favorable rate of heat transfer because of their greater heat storage capacity, which is sometimes referred to as thermal mass, or capacity insulation. Builders used this characteristic in their designs for centuries prior to the development of modern air conditioning methods, which are capable of overcoming less efficient designs at the cost of increased fuel use.
Aesthetics – Color Options
Masonry provides a wide variety of colors for architectural variety and visual warmth. Traditional reds, browns, tans, grays, and other tones are available in a broad range of textures to create looks that are unique as well as timeless.
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