Deterioration+ of+Lime-Based+Mortar+Joints

Deterioration of Lime Based Mortar Joints //Ethan S. Fogle, BAE/MAE, Penn State 2015-16 // toc
 * City, State - Date 2012 **

=History of Lime Based Mortar= Masonry, in all its forms, is possibly one of the oldest and most prevalent building methods used throughout history. Whether used for enclosure or foundation, cladding or aesthetic, masonry is an integral part of almost all historic buildings. As permanent as masonry may seem, it's weakest point can easily be the mortar with which it is laid. Even with proper preparation and construction methods, natural elements and other factors can still cause the deterioration of lime based mortars and thus, the deterioration or failure of the masonry structure (Mack and Speweik, 1988).

The first use of mortar with masonry is probably indeterminable, however there is some evidence of a burnt gypsum type mortar used in the Egyptian pyramids (Erlin and Hime 1987). This would date one of the earliest uses of lime as a construction material to around 4000 B.C. Originally mortar was made simply from adding lime (which is simply burnt limestone) and sand together and mixing with water. This mixture essentially hardens itself back into limestone, with the help of carbon dioxide. This process takes a long time and is unable to occur under water or even in very wet conditions ("History of Lime in Mortar").

The Roman Empire was one of the largest civilizations ever to build on the earth and while they may not have been the first to use lime in mortar they did use it extensively and developed guidelines for use. They also created different types of mortar for different purposes, such as building where water was an issue (aqueducts, cisterns, etc.). This was the first documented use of hydraulic mortars and a big step in the use of pozzolan, generally in the form of brick dust or volcanic ash ("History of Lime in Mortar"). Pozzolan is defined as a siliceous or siliceous and aluminous material which, in itself, possesses little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically with calcium hydroxide at ordinary temperature to form compounds possessing cementitious properties. The use of these additives by the Romans led to some of the biggest advancements in mortar production and performance.

Most of the following developments revolved around the refinement of the material that was added to the mortar, specifically the type of limestone, the addition of pozzolans, and the relative amounts of these materials. A few of the large discoveries that occurred in the 18th and 19th centuries can be seen in Table 1.


 * Table 1: Notable advancements in mortar production in the 18th and 19th centuries -** developed from "History of Lime in Mortar"
 * ~ **Discovery** ||~ **Inventor** ||~ **Date** ||~ **Notes** ||
 * Hydraulic Lime || James Smeaton || 1756 || developed from burning limestone containing clays, Smeaton specifically used Blue Lias limestone ||
 * Roman or natural cement || James Parker || 1796 || burning limestone and clay together, mixture was ground and stored (kept dry), better strength development through higher clay content (also great for wet building conditions ||
 * Portland cement || Joseph Aspdin || 1824 || controlled mix of limestone, clay, and other minerals; replaced natural cements and when mixed with lime provided workability and strength which allowed it to replace natural cements ||

Mortar mixes have continued to be refined since the advent of Portland cement but largely this has been in efforts to standardize the production. Builders are now able to tailor their mortar mixes to adjust for different building conditions (in terms of wetness) and different strength requirements. This is able to be done through combinations set by the ASTM C270 standard that set forth possibly one of the most common phrases in the masonry industry: MASON WORK, in which every other letter (M,S,N,O,K) denotes the different types of mortar in descending levels of compressive strength. ASTM C270 was developed in 1951 and is still in use today ("History of Lime in Mortar").

=Deterioration of Lime Based Mortar= Mortar deterioration in any form can be caused by a variety of issues. From something as simple as a leaking gutter to the differential settlement of a building, it can sometimes be difficult to pinpoint the exact reason why the mortar is failing. For this reason, the Technical Preservation Services of the National Park Service recommends that a consultant be utilized to asses the building and determine a solution specific to its context (Mack and Speweik, 1988).

Arguably the most common cause of failure mortar failure is due to moisture. When moisture is allowed to remain in the masonry for extended periods of time it can lead to binder leaching. This leaves the mortar with reduced strength and adhesion properties which obviously can lead to serious problems. As moisture lingers in the masonry it will tend to dissolve any of the soluble components of the mortar. The components most impacted are portlandite (calcium hydroxide) and calcite (calcium carbonate). As these components are dissolved they will simply exit the material with the water and be deposited elsewhere (Forester et al. 2014). If these soluble components are deposited within the masonry units themselves they cant create a problem called crystallization. This is an expansive process and it will add stresses to the masonry units. (Mack and Speweik 1988). Moisture present in the mortar also makes it susceptible to thermal changes which can the be impacted by freeze-thaw cycles (Castellano et al. 1994). While leaching will simply take the binding agents out of the mortar, freeze-thaw cycles will immediately put physical stresses on the mortar, similar to crystallization. Water will expand as it freezes into ice and this will cause movement within the mortar joints that, if large enough, cannot be accepted by the brick or mortar, causing cracking.

Moisture not only causes problems from physically being inside the mortar, but also chemically through process of ettringite and/or thaumasite production. This is an expansive chemical reaction (again putting unnecessary stresses on the masonry) that occurs in moist conditions (Loughran 2006). These are caused by a "reaction between sulfate salts and hydrated calcium silicates or aluminates which are present in mortars based on cement, hydraulic lime or lime-pozzolan" (Castellano et al. 1994). The sulfate salts can come from a variety of sources: brick impurities, water drawn into the masonry through capillary action, and the presence of environmental SO2 (generally garnered through air pollution). Hydrated calcium silicates or aluminates come from the mortar itself through the hydration process of Portland cement.

Evidence and Consequences
Despite the difficulties in determining the cause of mortar failure, the signs are usually quite evident and may help point out the cause. Each different cause of failure can have its own specific evidence, or all the evidence could point to multiple causes. However the case, failure can usually be prevented as deterioration is usually a very visual occurrence. It is very easy to tell if the mortar itself is deteriorating. It will be cracked, chipped, or could even be crumbling or falling out of the joints. Inadequate mortar (either produced inadequately or that deteriorated to the point of inadequacy) will be powdery and break apart very easily, lacking cohesion (Lew and Phan 2006). The failure of the mortar can also result in the failure of the masonry it is supporting. The masonry units themselves could be cracked, spalled or delaminated, indicating possible mortar issues (Mack and Speweik 1988). For example, if a mortar joint is constantly subjected to even slightly wet conditions along with a repetitive freeze-thaw cycle that causes the joint to expand and contract, this will put extra stresses on the masonry units and can cause them to spall, loosen or pop out, crack or even crush (this is also the case with crystallization). These same type of issues can arise from binder leaching. As the mortar loses its binding strength, it can disengage from the masonry units, thus reducing the overall strength of the wall (Forester et al. 2014). Some images can be seen below in Figures 1 - 9 of different types of mortar and masonry failure.



Figures 1 - 9 are images taken by the author

=Failures/Case studies=

Elks Lodge Building Collapse
On Monday, June 26, 2006 the Elks Lodge Building in Clinton, Missouri collapsed with about 50 people inside at the time. All but 10 managed to escape and of these, 9 were rescued. There was one fatality (Casey et al. 2006). The Lodge Building, build in the 1880's was 4 stories of unreinforced brick. Figures 10, 11, and 12 detail plans and a section of the building noting dimensions and materials. The 13 inch bearing walls (east and west walls) were common walls between the lodge and the adjacent buildings. From the bearing walls, wooden joists spanned about 20 ft to a wooden beam which in turn spanned between cast iron columns. These columns were spaced at 18 ft on center and were on levels 1, 2 and 3. The 3rd level had roof joists that spanned from bearing wall to bearing wall, creating a more open floor plan.



Figures 10 - 12 created based on Lew and Phan, "A Summary of Reconnaissance of the Clinton, MO Elks Lodge Building Collapse on June 26, 2006".

The collapse was cause by the failure of the west wall which in turn caused the roof and floors below to fail. When the west wall went down this caused a partial failure of the Kreisler Drug Pharmacy building. This failure is an excellent example of the consequences faced when the mortar in a wall deteriorates. As the mortar deteriorated, it transferred the load from the floors and roof onto the individual bricks, rather than functioning as a whole. For a while this was probably not an issue, however as the wall was continuously exposed to moisture, and the mortar continued to deteriorate, the load became too great for the bricks to carry and they most likely crushed or broke into smaller pieces causing the collapse of the wall (Lew and Phan 2006). Figures 13 and 14 show the collapsed area and illustrate the complete loss of mortar adhesion (no wall segments remain in Figure 13) and the moisture problems that caused the collapse (Figures 14).



Figures 13 and 14 courtesy of Tim Gardner, Executive General Adjuster, Regional Manager, NHI General Adjusters

Majestic Theater Ceiling Collapse
Another example of failures resulting from deterioration of mortar joints is the Majestic Theater in Pittsburgh, PA. The building footprint was about 60' x 75' and the 13" thick bearing walls stood 50' tall. Figure 15 shows a general overview of the building layout. The roof consisted of trusses spanning the 60' dimension of the building. Between the trusses spanned 2 x 6 joists that were notched to bear on 1 x 3 strips nailed to the sides of the bottom chord of the roof trusses. Figure 16 shows a figure detailing this connection. These joists supported the ceiling of the building, which was added when the building was converted from the church it was originally constructed as. The ceiling consisted was wooden lathe that was plastered for the finish. At the time of incident, the endwall was bowed out nearly a foot. This was thought to have been caused by the addition of the ceiling as the bow was not recent but had the wall bowed before the addition of the ceiling, it would have surely collapsed before the event. In addition, a steel channel had been added at about mid height of the wall that was clearly intended to restrain the wall from completely buckling. Regardless of the exact cause and timing of the bowing of the wall, it was most certainly initially caused by the poor lime mortar used in construction of the bearing wall. Despit e the apparent inspection and safety clearance of the building 2 weeks prior to the incident, there were still many, very noticeable issues (Godfrey 1992).

Figures 15 and 16 developed from Godfrey, "Buckling Wall of Theater Causes Ceiling Collapse"

"The rubble wall at the back of the end wall has very little mortar in the joints. The mortar in the brick wall can be picked out easily with a knife. The partition wall is cracked away from the end wall with a wide-open crack. Large cracks appear in the side walls near the end of the building, evident both inside and outside of the building;they are old cracks, for they are full of dirt" (Godfrey 1992).

As this wall bowed out further and further, it pulled the truss closest to it (which it was anchored to with anchor rods; but only to this truss) out away from the rest of the trusses. This resulted in the loss of support of the joists and eventually the collapse of the ceiling panel (Godfrey 1992).

The Campanile Venice
On July 14, 1902 the Campanile of St. Mark's at Venice collapsed. The history of this tower is quite extensive and the spot it marks has been the site of a tower for for fourteen centuries. It first started as a defense tower built into the walls of the city. It was fortified in the ninth century; after being built in the sixth century it needed refortified and thus the foundations needed strengthening. Not long after this the tower was converted into a bell tower, or Campanile. The tower received something close to its final aesthetic in 1510 when it was damaged by an earthquake, causing the rebuild of almost the entire shaft. When the structure collapsed it was almost impossible to discern the initial cause however, it is stated that "the fall of a structure which has stood through many centuries without any known direct causative influence, must be the result of a gradual decay of the material" ("Rebuilding" 1908). This is a very probable theory as the moist sea salt air would give the wall plenty of moisture to take in through capillary action if nothing else ("Rebuilding" 1908). Around the time of the collapse, during repair work it was found that through incorrect repair work, the mortar had become the structural support (as opposed to the masonry units) for the tower (MacCollum and Hughes 2005).

=Prevention= Preventing mortar deterioration begins with the determination of the cause. What may work to fix one issue, may not be the correct fix for another issue. In the case of settlement issues, there may be foundation work required before proper installation of the masonry can be completed. It may be possible to address the issue with the addition of expansion joints as well and these may be used to effectively break up long panels that are subject to large movements due to expansion and contraction, in any of its forms. The first step in moisture protection would be to ensure that the masonry is not being exposed to any unnecessary amounts of moisture. This would involve installing or repairing flashing, or providing proper weep holes for moisture to escape the wall without causing problems in the masonry itself. It is however, impossible to keep the masonry from picking up any moisture. Through natural instances such as wind-driven rain and even capillary action of the humidity in the air, moisture will always find its way into a wall. Because of this fact, mortar selection is critical, whether for new construction or repair of existing or historical masonry. These issues are discussed in the **Repair** section.

=Repair= It must first be noted that in some cases, repair should be considered one in the same with prevention. For example, it will do no good to repoint a section of water damaged masonry, if it is flashed improperly, without first installing proper flashing to prevent future damage. That being said, the actual repair of lime-based mortar is a process that requires appropriate planning and skill to complete effectively. Generally, as long as there are no glaring structural issues (differential settlement, improper initial construction, etc.) the mortar will be repaired with a method called repointing or sometimes just pointing. This is "the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar" (Mack and Speweik 1988).

After any immediate structural issues are addressed, and proper prevention steps taken, the most critical step especially when dealing with historic structures, is matching the existing mortar. This is not only important for the right aesthetic but also serves some other very important functions to the performance of the mortar once in the wall. Mack and Speweiks "Repointing Mortar Joints in Historic Masonry Buildings" notes the criteria that a replacement mortar must conform to in order to achieve the desired outcome:
 * The new mortar must match the historic mortar in color, texture and tooling.
 * The sand must match the sand in the historic mortar. (The color and texture of the new mortar will usually fall into place if the sand is matched successfully.)
 * The new mortar must have greater vapor permeability and be softer (measured in compressive strength) than the masonry units.
 * The new mortar must be as vapor permeable and as soft or softer (measured in compressive strength) than the historic mortar. (Softness or hardness is not necessarily an indication of permeability; old, hard lime mortars can still retain high permeability.)

These requirements place a heavy focus on material selection and the specific types especially. As noted above, the sand will play the biggest role in color and texture of mortar while the other additives will have a larger impact on the strength and permeability of the mortar. Strength of the mortar is so important because it is effectively the expansion joint between every brick, it will accept the movements caused by moisture, settlement etc. If a mortar is too hard, harder than the masonry units, it will not be able to act as this expansion joint and thus the stresses will be put into the masonry units themselves. It is rather easy to fix a mortar joint in comparison to fixing a cracked or crushed brick because the mortar put too much stress on it. The ability for vapor or moisture to permeate the mortar is also very important. This ties back to the crystallization issues that can take place in masonry. If the moisture is not able to escape through the mortar joints it will travel through the masonry which may deposit soluble salts that can crystallize, causing expansion and thus damage to the masonry units in the form of spalling, cracking etc (Mack and Speweiks 1988).

=Conclusion= Masonry can be an incredibly versatile and long-lasting material. This is evident in its longevity of use. From the days of the Egyptians and the Roman Empire, up through the modern age, masonry has been an integral part of the building process. While its materials, construction process and role within a building may have changed throughout time, its usefulness cannot be argued. These qualities do not come completely free however. For masonry to stand the test of time, proper planning during the building process and the correct maintenance, repair, and restoration must take place. Mortar is arguably the component that can play the biggest role in the performance of a masonry structure. From, strength and adhesion, to moisture penetration and escape, the mortar must perform as necessary for the wall to function at all.

=Bibliography=


 * Casey, Rick; Christy, Joseph; Ellis David; and Wade, Jacob. (December 1, 2006). "Elks Lodge Building Collapse." //EMS World//.** **<**[]**> (accessed October 10, 2015).**
 * First responder report, details of the condition that was found.


 * Castellano, M.G.; Collepardi, M.; Moriconi, G. (1994). "Mortar deterioration of the masonry walls in historic buildings. A case history: Vanvitelli's Mole in Ancona" //Materials and Structures.// 27,408-414.**
 * An analysis of the deterioration of a historic structure (Vanvitelli's Mole in Ancona) through a combination of x-ray diffraction and historical sources and environmental information.


 * Erlin, Bernard; and Hime, William G. (1987). "Evaluating Mortar Deterioration." //APT Bulletin.// 19(4), 8-10.**
 * <**[]** > (accessed October 10, 2015). **
 * A brief history of mortar use followed by a good source for the actual testing of mortar in evaluation of deterioration.


 * Forster, Alan M.; Szadurski, Ewan M.; Banfill, Phillip F.G. (March 25, 2014). "Deterioration of natural hydraulic lime mortars, I: Effects of chemically accelerated leaching on physical and mechanical properties of uncarbonated materials." //Elsevier: Construction and Building Materials//. 72(1), 199-207.**
 * An article that goes in depth on the testing of binders and their leaching properties.


 * Godfrey, Edward. (May 25, 1992). "Buckling Wall of Theater Causes Ceiling Collapse." //Engineering News Record//. Volume LXXXVIII, 873.**
 * <**[]** > (accessed October 11, 2015). **
 * A very thorough report about the conditions of the Majestic Theater before and after the collapse. Very detailed description of the structure and the mode of failure.


 * "History of Lime in Mortar" N.A. //Graymont//. <**[]**> (accessed on November 12, 2015).**
 * Gives an in depth history of lime mortar and it's evolution in the building industry. Excellent resource for both the manufacture and use in the construction process.

**Lew, Hai S.; and Phan, Dr Long T. (July 2006). "A Summary of Reconnaissance of the Clinton, MO Elks Lodge Building Collapse on June 26, 2006." //International Journal of Web Services Research//.**
 * Details of events including building specifics, collapse and photos of the, comprehensive report of failure.


 * Loughran, Patrick. (2006). "Failed Stone: Problems and Solutions with Concrete and Masonry" //Birkhauser - Publishers for Architecture//. 105,108. < ** __ [|https://books.google.com/books?id=vWLRAAAAQBAJ&pg=PA105&lpg=PA105&dq=ettringite+in+masonry+failure&source=bl&ots=89AuIlBfGF&sig=qfnjtCFd5IxwDZDMAZN3P4KMCHc&hl=en&sa=X&ved=0ahUKEwi34euL5tfJAhWFMSYKHVKNCVwQ6AEILjAD#v=onepage&q=ettringite&f=false] __ **> (accessed on December 1, 2015).**
 * A comprehensive look at failure issues in masonry and concrete. Simplified description of ettringite an thaumasite in masonry.


 * MacCollum, David V.; and Hughes, Richard T. (2005). "Building Design and Construction Hazards." //Lawyers & Judges Publishing Company.// 434-435. <**[|https://books.google.com/books?id=0a2byo0hi9sC&pg=PA435&lpg=PA435&dq=majestic+theater+pittsburgh+collapse&source=bl&ots=sC1FPH_gey&sig=_JHFUA2Y3J2gvie25dQd3oQKpCE&hl=en&sa=X&ved=0CCcQ6AEwA2oVChMIlfWQ9sKvyAIVS-iACh2QGAF4%20-%20v=onepage&q=majestic%20theater%20pittsburgh%20collapse&f=false#v=onepage&q&f=false]**> (accessed on October 11, 2015).**
 * Overall look at building construction issues. Small section on the Majestic Theater failure.


 * Mack, Robert C.; and Speweik, John P. (October 1988). "Repointing Mortar Joints in Historic Masonry Buildings" //NPS Department of the Interior - Technical Preservation Services - Preservation Briefs #2.// ****< **[]**> (accessed October 11, 2015). **
 * Identifying mortar problems, properties and analysis of mortar (resource for other preservation topics). Excellent scope for the repair work in historic masonry.


 * "The Rebuilding of the Campanile of St. Mark's at Venice." (September 24, 1908). //Engineering News.// Volume 60(13),323-324. <** __ [|https://books.google.com/books?id=SDRKAQAAMAAJ&pg=PA323&lpg=PA323&dq=the+campanile+venice+mortar+problems&source=bl&ots=bEsx_bMk1X&sig=AxaQ8dbcWgucuiTbEiFXLVnecDM&hl=en&sa=X&ved=0ahUKEwiNvZfz89HJAhUEQiYKHXNJCEMQ6AEINTAG#v=onepage&q=the%20campanile%20venice%20mortar%20problems&f=false] __ **> (accessed on December 1, 2015).**
 * Article detailing the history and collapse of the Campanile at Venice.

=**Additional Resources**=


 * "Elks Collapse brings change to small town." (July 23, 2006). //Columbia Daily Tribune.//** **<**[]**> (accessed October 10, 2015).**
 * Aftermath of collapse for the town


 * Grimmer, Anne E. (1984). "A Glossary of Historic Masonry Deterioration Problems and Preservation Treatments." //Department of the Interior National Park Service Preservation Assistance Division.// **
 * A comprehensive guide to the types of failure common to masonry, fairly specific to masonry unit failure but a good resource as mortar can sometimes be the cause of these issues