Posts Tagged historic preservation
Your hands were blistered, your head dripping with sweat. It had taken a day, or two, maybe three, to create something you now hold in your hand to secure your short-term job-site future. You likely thought about its design and function in your head as long as it took to cut and weld it together with the best steel or iron you could find. A chisel. Not just any chisel, a stonemasons chisel.
Your chisel – its size, and weight to fit your hand – an extension of yourself. Made for the specific work you were paid to perform. Created for a specific type of stone. The chisel shape, length, and sharpness all part of its design and intended purpose to birth a dimension stone of specified measurements and texture worthy of setting into a historic masonry wall. To become an important part of another historic stone masonry building of load bearing capacity, carrying the weight of each consecutive floor upon itself as it raises from the ground on the stout foundation we never see or appreciate.
The creation of stone chisels at the construction site by the very stonemasons that use them is centuries old. And it probably is most definitely on the road to oblivion. The art of the stone masonry craft is now changed. Making tools at the construction site, or in the stonemasons workshop, was part of the trade. It was what you were trained to do 100 years ago. There were no other options. And for good reason, no one else would know what you needed for a specific project as each individual set of chisels were designed specifically for each job. If you have the privileged of knowing a retired stonemason – just look in his tool bag and confirm for yourself – there are many many chisels of various sorts.
Stone chisels; however, now are made by others. People that are not in the stone masonry trade. They can not appreciate the purpose of the chisel design or its intended purpose because they are not stonemasons.
Blame it on changes in architectural design: Veneer walls and thin stucco stone are in, old-fashion load-bearing walls are out. Blame it on changes in the father-son connection: handing down the trade skills to the next generation. Blame it on the fact that nothing lasts forever, not even tool making skills of the simple chisel lodged in the brain of almost every American stonemason over 80.
True American-made stone masonry chisels can not be found at Home Depot, Lowes, Menards or your local hardware stores. But don’t blame these companies they serve a different customer base – the “Do-it-Yourselfer.”
As a professional in your trade, part of your job is to research and look for those American companies that still do exist that make the custom tools you need – especially the all important chisel.
I have known Norm Akley, President of Trow & Holden Company, Inc., for nearly 20 years. He operates a company located in Barre, Vermont that makes old fashioned hand-made stone chisels among other items for the trade. Norm understands my trade and the challenges I face in difficult projects. I draw a picture of a special chisel design I need to have fabricated for a particular project to match a historic profile finish and fax it over to him, yes I said fax!
He makes the chisel from my sketch in the correct size and weight and the rest is history! Speaking of history, Trow & Holden Company has been making stoneworking tools since 1890.
Every chance I get I try to support American companies like Trow & Holden. The experience in tool making, as well as the companies appreciation and knowledge of my stone masonry trade, make Norm and his company a very valuable partner in our ability to offer the best Historic Stone Masonry Training Programs in the United States. In the end, I believe better workmanship is a direct result of better tools in the hands of craftspeople who know how to use them correctly.
Anguish for descendant of Victorian artist as stone splits in two during restoration work
Art lecturer Ian Wilson with the broken gravestone
Victorian Pre-Raphaelite artist Ford Madox Brown. Right: Great-great-grandson Oliver Soskice
Published: 29 March, 2013
by PETER GRUNER
THE great-great-grandson of Victorian Pre-Raphaelite artist Ford Madox Brown has voiced concern that the gravestone of his famous ancestor has been badly damaged during restoration work.
Oliver Soskice, 64, a professional artist, paid £750 to have the stone – which was leaning perilously – placed flat on the ground at Islington and St Pancras Cemetery, in East Finchley.
However, during lifting work last month the ornate stone broke into two pieces and that is how it has been left.
Mr Soskice said: “It’s not that I tipped Hamlet’s gravedigger £10 to do the job. The work cost a lot of money.
“I wanted them to clear the site, which they have done, and lay the stone flat on the ground so there was no danger it might topple over and injure someone. But I had no idea there was a danger it might break.”
Mr Soskice, who lives in Cambridge, is the son of Frank Soskice, the late Labour MP and former Home Secretary.
The “forgotten and neglected” Madox Brown burial spot was discovered by chance by Holloway art lecturer Ian Wilson while visiting his mother’s grave nearby in March last year.
As a result of Mr Soskice’s concerns, featured in the Tribune last year, Islington Council launched a Ford Madox Brown grave improvement appeal.
Mr Wilson, art co-ordinator at the Hoffman Foundation for Autism in Wood Green, hopes the appeal will pay for repairs to the stone and the eventual full restoration of the grave. He said: “At the moment the grave looks like a building yard. This is disrespectful to anyone let alone an important British artist and early socialist.”
He has asked the council’s environment chief, Councillor Paul Smith, to instigate work cementing the two broken parts of the stone together.
“Cllr Smith was reported last year in the Tribune as saying he was keen on launching an appeal,” he said. “How far has he got?”
Cllr Smith said this week he was sorry the stone had broken and hoped it could be repaired.
“I hope to meet the family as soon as possible and get the appeal going,” he added. “This important piece of art history needs to be supported.”
Speweik Comment: This story was first posted by Jonathan Appell on LinkedIn Group “Gravestone & Monument Preservation.” April 7, 2013. It was refreshing (but sad) to see a published story in a newspaper about a historic stone repair gone wrong. Maybe it was because it was a gravestone, and maybe it was because it was a famous persons gravestone, or maybe because it was so old – at this point it doesn’t matter – I’m just glad it was published for all to read. We can learn from the mistakes of others when we have the opportunity to know about them. A true expert (if such a person exists) is one that has a strong character trait to admit a mistake and allow others to learn from his experience. This of course is not usually our natural response.
Coming from the trades as a stonemason, I have come to learn and respect stone by working with it for many years in many applications. From quarry, to block, to slab, to dimension unit, to seasoning of the stone, then protecting and preparation, and finally to the installation into the wall. I have also had the reverse experience in my later years in historic preservation work of carefully deconstructing, removing from the wall, redressing, restoring, rehabilitating, and conserving stone for reuse – placed back into the same location or position.
I have found that historic preservation work requires a higher-level of sensitivity to the task with the baseline understanding that you are handling history and not just a piece of stone.
I have come to appreciate that the preservation approach must be well thought out and planned by first identifying the stone. Then determine the cause of the problem and possible pattern(s) to similar surrounding stone. Then examine the historic stone for potential areas of weakness prior to establishing the proposed solution to the problem – and certainly before moving it. It is from this process and examination (Condition Assessment) is HOW I develop the respect for the stone, what it has been through in connection to its problematic condition and then to finalize my proposed options for solutions.
This approach helps to keep surprises to a minimum, not to say they still do not occur, but hopefully not to the degree we read in this story.
I see some key contractor/owner errors or “red flags” in this story that may have made the initial problem more complicated. Can you identify some of these flags? Both on the contractor side and the owner side? I would love to hear your experiences with similar projects. Remember sharing any mistakes is a good thing here 🙂 Who will be my first expert to comment??
An Interview with Lauren McCroskey, U.S. Army Corps of Engineers – Revised UFGS Historic Masonry Specification
I had the unique privilege to interview one of the leading historic preservation experts, Lauren McCroskey, Program Manager, for the U.S. Army Corps of Engineers, at the Seattle District, on the recent revision to the UFGS for the Restoration and Cleaning of Masonry in Historic Structures.
USACE Official Announcement:
Technical Center of Expertise (TCX), Preservation of Historic Structures and Buildings Technology Update
As part of its mission to provide leadership in historic buildings technology, the TCX announces a major revision of its specification, “Restoration and Cleaning of Masonry in Historic Structures.” The spec now reflects state-of-the-industry guidance for the treatment of historic masonry and mortar, and surpasses existing preservation guidance provided by other federal agencies.
Property managers and cultural resource specialists are encouraged to use the spec in contract documents to ensure that masonry work is performed appropriately to prolong the life of historic buildings. See Unified Facilities Guide Specification 04 01 00.91
Speweik: What is the official title of the specification?
McCroskey: The title is the UNIFIED FACILITIES GUIDE SPECIFICATIONS
DIVISION 04 – MASONRY SECTION 04 01 00.91
RESTORATION AND CLEANING OF MASONRY IN HISTORIC STRUCTURES
Speweik: Who originally authored it?
McCroskey: The Corps was the preparing agent and performed the processing. The exact author(s) are unknown, though Corps staff would have prepared it.
Speweik: How long has it been in use/circulation?
McCroskey: It’s been available since 1991.
Speweik: Who is authorized to use it?
McCroskey: The Guide is to be used by the Military Departments (Army, Navy, Air Force, etc.), the Defense Agencies and the DoD Field Activities for planning, design, construction, sustainment, restoration and modernization of facilities, regardless of funding source. But anyone can use the guide to adapt to a particular masonry project.
Speweik: What government agency owns it?
McCroskey: The Architectural Discipline Working Group are the owners of the Section; Scott Wick is the Corps representative of that group.
Speweik: What is your position with the USACE and what specific responsibilities do you have regarding historic preservation?
McCroskey: I manage the Technical Center of Expertise for the Preservation of Historic Structures and Buildings, a program of nationwide service. The program provides technical assistance and preservation planning for Corps Districts, DoD, and other federal agencies to ensure facility and property managers apply the best practices to historic structures. We try to set the highest standards of preservation practice through quality project work, training, and by developing technical information.
Speweik: What prompted you to request an update to the Historic Masonry Division Section this past year?
McCroskey: For several years I’ve had an awareness that the Corps’ existing standards and guidance for the treatment of historic masonry has lagged behind newer developments and technological advancements for treating historic brick, stone, and mortar. I receive inquiries from Corps Districts and other agencies asking for specific guidance to address deteriorated stone or brick. Property managers rarely know how to approach these issues from a historic preservation perspective, and often have maintenance and field crews tackle masonry problems. While their intent is good, the methods, materials, and applications are often not appropriate for historic structures, and can lead to further harm and long-term costly repairs. That’s why it’s essential for us to be able to pass along the most appropriate, state-of-the-industry techniques and standards.
Speweik: What do you believe to be one of the most significant changes to the specification?
McCroskey: There are many improvements, but one of the most important is the depth of information, which is far more educational for the user than the old spec. There is much to be learned from this document. Another key improvement is that materials application is not just described, but preceded by a thoughtful examination of building and masonry conditions. There is extensive information about how to investigate existing conditions so that the best decisions can be made about materials, conditions, and methods.
Speweik: How do you see this change making a positive difference for the quality-level of Historic Preservation Projects in the United States?
McCroskey: I believe the TCX is obligated to provide the best guidance regarding the treatment of historic structures and buildings. By encouraging the use of this guide, the rehabilitation of historic masonry should be performed in a manner that is appropriate, efficient, and prolongs the life of historic materials.
Speweik: How do you envision the revised specification affecting the work you do at the USACE?
McCroskey: The spec will be the only guidance we provide to customers, or when advising others on the best standards for masonry. Since this spec now surpasses all other historic masonry guidance, we now consider this document the “gold standard.” Of course, there are sub categories of masonry, such as terra cotta and concrete, which may require other technical information. But where brick, stone, and mortar are concerned, this is our “go to” standard.
Speweik: Did you consider the possible additional costs to Historic Preservation Projects as a result of some of the changes? And, if so, do you believe the additional cost is a significant percentage of overall project costs?
McCroskey: When good preservation practices are used, the life and performance of historic materials is extended. When improper practices are applied, greater costs can be incurred when the wrong treatment or method causes damage that requires repair. Taking short cuts by using commercial products that are not suited to historic stone or brick, or using techniques that are not consistent with historic methods can cost more long-term, and rarely satisfy the Secretary of the Interior’s Standards for Rehabilitation and treatment of historic structures that all federal agencies must follow.
Speweik: How do architects, owners, consultants and contractors find out more about this important specification document?
McCroskey: The guide is now available on-line at the TCX web page: http://www.nws.usace.army.mil/BusinessWithUs/HistoricPreservation.aspx
For additional information or clarification regarding the spec’s application, your readers may contact me at:
Technical Center of Expertise
Preservation of Historic Structures & Buildings
U.S. Army Corps of Engineers
I encourage the next generation of future masons to always look for opportunities to embrace mentors in our trade. And to the older masons I say make a difference in the world of a young person looking for a trade and openly share your professional experience in masonry knowledge in the preservation of important historic architecture. We each bring to the table a skill set that can, and will, make a difference – if, or course, we are given the chance and awarded the projects we seek to secure.
Many of you may not know about my background and experience in masonry preservation – so I will provide you with just a brief overview of how I ended up where I am today with the title of: “Historic Masonry Preservation Specialist” I grew up in the masonry construction business working for my father, uncles, and grandfather in a family owned business located in Toledo, Ohio. This opportunity to be birthed into a family of working brick and stonemasons was not by choice but to keep me out of trouble in my teenage years. And yes, it did work. There is something about carrying brick and stone, building scaffolding, mixing mortar, and cleaning out the toolbox that keeps one honest. I think I was just to tired after working all day to have the energy to get into trouble as I learned the trade of masonry construction is most demanding on the body.
As it turns out I developed a lower back injury that kept me from working in the trade actively – so I decided to go back to school and study architecture. It was in college that I began to appreciate the art of design and the process of construction as it related to historic and traditional masonry architecture. If I could no longer lift and set the stone – I could learn about how to preserve its original condition – and more importantly to do this in the means and methods of the original builders. This meant I needed to be willing to learn about traditional masonry construction tools, methods and materials. It also meant I needed to find other masons that understood these aspects of my new desire. The year was 1990 – 26 years ago. I researched my own family of origin in the masonry trade which dates back to 1870 in Posen, Prussia. So I was the 5th generation in my family to be involved in the masonry business. The problem; however, was that the oldest living relative that would had known about traditional masonry construction methods, workmanship, and materials was my great grandfather and he died in 1951. My grandfather died in 1979; my father in 1985.
As luck would have it I secured a job at a lime manufacturing company in 1991. It was during my employment I discovered an enthusiasm for historic mortar materials, which of course are based upon lime, and have been for thousands of years. Working with several conservators, architects, and a masonry contractor based in Toronto, Canada I began offering lime putty for use as a binder (without Portland cement) combined with sand at the jobsite. It was not long after; however, that I realized the need to train masons on the jobsite to use the Portland-free mix design and assist them in delivering the best quality possible. I traveled to England, Ireland, and Scotland over the next several years to work alongside other masons who generously mentored me in preserving historic masonry using lime mortars and traditional methods on castles. Then I brought that information back to the United States to assist in our training efforts here. That was 1998.
We made mistakes; we learned from our mistakes, we improved our methods, tools, equipment and materials. We did not give up. Encouraged from my mentor masons in Europe and Canada – I completed one project after another across the United States monitoring the progress as I went along. Writing, speaking and communicating with industry professionals I stayed focused. I wish to gratefully thank the pioneers in the masonry preservation movement in Europe that encouraged and personnally helped me like; R.H. Bennett, MBE, Winchester, England; Dr. Gerard Lynch, London, England; Mr. Douglas Johnston, Glasgow, Scotland; Mr. Patrick McAfee, Dublin, Ireland; Ms. Pat Gibbons; Charleston Fife, Scotland; the late Mr. John Ashurst, London, England; Mr. John Fidler, York, England; Mr. Colin Burns, Manchester, England; Mr. Stafford Holmes, London, England; Mr. Tim Meek, Charleston Fife, Scotland; Mr. Michael Wingate, England; Mr. Sam Trigila, Toronto, Ontario, Canada; Scottish Lime Centre; and English Heritage and the Society of the Protection of Ancient Buildings (SPAB) in London, England.
Since the early 90s I have been privileged to assist in the effort to establish (or best said, re-introduce) the lost art of true traditional masonry preservation with the use of lime mortars leading the way. As we continue this effort in 2016 we will actively be searching for architects and historic building owners that seek to preserve the architectural history and character of their properties by supporting the masons by offering onsite historic masonry training that is project specific. I strongly believe that by understanding our past and acknowledging the workmanship, trade practices, techniques, and tools used by the original masons in the process of the original construction we will have a better chance at success in the authentic preservation of historic masonry.
If we go into historic masonry preservation projects expecting that masons today should know all the details that are vital to the success of a masonry preservation project – I think we are asking for too much – especially in a low-bid environment in which many design professionals must deliver their services. Let us expect the best, write excellent specifications to support quality assurance – but we must be realistic in the understanding of what that actually means to the mason working at the site. In many cases these men and women have never worked with a straight pure lime mortar before so there is a natural learning curve that must be acknowledged. But we can not, and should not, let masonry contractors figure it out on the jobsite without proper guidence. This is why I started my company to do just that – mentor and help the masons through training. The same way I learned in Europe.
Speweik Preservation Consultants are not masonry contractors. We use our hands-on historic masonry experience to provide the necessary technical consulting services in: condition assessment, material testing, specification assistance and masonry contractor training at the project site. We strive to support the efforts of the Architects and Historic Building Owners in meeting the US Department of the Interior’s Secretary Standards for Rehabilitation in Division 4 and to protect the historic integrity of the architecture under repair consideration.
Mortar analysis can be done various ways with several different approaches to identify the original mortar ingredients of a formulation. However, there are limitations and replacement mortar specifications should not be based solely on laboratory analysis. Analysis requires interpretation, and there are important factors which affect the condition and performance of the mortar that cannot be established through laboratory analysis. These may include: the original water content, rate of curing, weather conditions during original construction, the method of mixing and placing the mortar, and the cleanliness and condition of the sand (Pres. Brief 2 pg. 2).
Mortar can be evaluated by simple wet-chemistry of using hydrochloric acid and water to dissolve out the binder components (calcium carbonate) leaving only the sand particles behind. The ratio of binder to sand can be determined by drying the sample first then weighing it before and after the wet-chemistry process. The problem occurs when calcium carbonate is part of the sand component which would give you a false reading of the ratio. There is also x-ray diffraction, and petrographic analysis by microscope, as well as thin-section technology, where small samples of mortar are cut into very thin sections and dies are injected into the sample showing the different components of the mortar. In addition, ASTM C1324 is a test method to determine components of hardened mortar samples.
The most useful information that can come from a laboratory analysis is the identification of the sand by gradation and color. This allows the color and the texture of the mortar to be matched with some accuracy because sand is the largest ingredient by volume.
A simple non-technical evaluation of the masonry units and the mortar can provide information concerning the relative strength and permeability of each-critical factors in selecting the repointing mortar – while visual analysis of the historic mortar compared to the new replacement repointing mortar can be made. It’s important to match the un-weathered portions of the historic mortar in case the building will be cleaned in the future, or cleaning should be taken into account before the sample is matched.
After a careful evaluation and clear understanding of why the mortar joints have deteriorated (or not, in the case of removing hard portland cement mortars) it’s time to repoint the wall. First, is the question of how deep to cut the old mortar out from the joints in preparation to receive the new replacement mortar. The Preservation Brief 2 “Repointing Mortar Joints in Historic Masonry Buildings 1998 published by the U.S. Department of the Interior’s National Park Service , Heritage Preservation Services gives us a good place to start.
Old mortar should be removed to a minimum depth of 2 to 2-1/2 times the width of the joint to ensure an adequate bond and to prevent mortar “popouts”. For most brick joints, this will require removal of the mortar to a depth of approximately 1/2 to 1 inch; for stone masonry with wide joints, mortar may need to be removed to a depth of several inches. Any loose or disintegrated mortar beyond this minimum depth also should be removed”(page 9).
I like that the Brief advises on a range of mortar depths in correlation with the width of the joints. It makes sense to approach the removal in this way. Often I see contractors bidding repointing projects calling for the depth of the removal at ¾ inch. For most mortar joints that are the thickness of your little finger, about 3/8 inch, this is not deep enough. It does not cost the contractor any more money to remove another 1/4 inch of material during preparation and it makes for a better job.
Luckily for the projects requiring the removal of hard portland cement mortars from old historic lime mortar walls, the contractors of years past, did not follow this quality protocol of 2 to 2-1/2 times, otherwise the portland cement mortars would be much more difficult to remove. Instead, we most often find these projects only skim coated with the harder material. It is important as a mason contractor to know what you are getting into prior to bidding a project that has been pointed in portland cement. Questions you should be asking are; How deep is the non-original portland pointing?,… How hard is the mortar?,… and how difficult will it be to remove it without causing damage to the surrounding masonry units? Sometimes the only way to really know for sure about the answers to these questions is to commission a test panel prior to bid.
A four-step approach to removing mortar joints in historic masonry buildings has been the industry method and best practice approach now for the past 15 years or so. First, the use of thin diamond-blade (turbo-type) grinders has been successful in cutting down the center of the horizontal (bed) joints for the removal of hard portland cement mortars. Second, followed by hand hammer and chisels or pneumatic chisels, to remove the excess mortar from the top and bottom of the masonry units. The vertical (head) joints are removed by chisel and hammer once the bed joints are removed. The third step is to use a caulking cutter with a diamond sickle type blade to clean the top and bottom of the masonry units and create a square cut back to the original lime mortar.
In the fourth and final step, mortar debris from the process should be removed by compressed air or a vacuum system. We do not use large amounts of water to flush out the debris during the cooler fall or spring months as it takes a long time for the walls to dry out especially the north facing elevations that do not benefit from the direct sunlight. We have unintentionally had efflorescence become an issue on some projects – waking up salts that lie deep within the masonry wall system due to excess water flushing.
As the market increasingly becomes aware of the use of building lime for historic masonry restoration there will always be challenges in making sure everyone understands the decisions they are making, why, and most importantly, the materials they are working with. Take lime for instance, everyone seems to believe that going back to the old mixes of yesteryear is a better choice than that found in Isle 14 at the local Home Depot when it comes to mortar selection for historic masonry structures. But just knowing about a subject and really understanding a subject are two entirely different things. The product of lime is pretty basic. You have lime putty, purchased wet (Philadelphia cream cheese consistency) in a bucket or barrel, and you have dry hydrate lime purchased in a 50lbs. (fifty pound) bags (fluffy and very light weight).
Common cement/lime mortar mix formulations in the restoration industry center around 1:1:6; 1:2:9; and 1:3:12 (Type N, O, and K respectively- ASTM C270-10, proportion specification). The second numeral reflects the amount of lime to be added to the formulation to create the desired mortar and thus the characteristics of that mortar. Generally, a mortar with more lime will tend to have better workability, higher flexural bond and more autogenious healing properties than a mortar with less. If its compressive strength your after than 1:1:6 is your answer, if you are looking for the flexibility to accommodate for future movement than you will likely be happy with a 1:2:9 or 1:3:12 formula. And then of course there is the historic straight 1:2.5 lime-sand mortar almost always made with lime putty and not dry hydrate lime, let me explain one of the reasons why.
Lime, like portland cement, is measured as a dry powder when mixing individual ingredients at the job site. Small batches of mortar are mixed from opened bags using a coffee can or some other used drinking cup (seven-eleven big gulp cup works good) up to a five gallon bucket depending of the project needs. But here’s the real scoop – Dry hydrate lime experiences a significant volumetric loss when converted to a wet paste during mixing. Let me say that again, Dry hydrate lime experiences a significant volumetric loss when converted to a wet paste during mixing. Volume changes that occur when dry hydrated lime is converted to a wet paste can cause sizable errors in proportioning mortar formulations; the most likely error is over-sanding.
A given amount of hydrated lime occupies far more volume as a dry powder than it does after mixing with water. Thus, when lime is measured as a dry powder, less is actually put into the mixture than is used if the lime is measured as putty. When wetted, dry hydrate lime will typically contract, on average, to 75% of the original dry volume. Using a nominal 1:2:9 mixture (Type O) cement/lime/sand, the variation caused by wet verses dry measure of the lime results in a 1:1.5:9 mixture. This ratio exceeds the allowable sand content in ASTM C270 of 2.5 to 3 times the binder, and is actually 3.6 times the cement plus lime; thus an unintended over-sanded mixture results. To avoid this problem an additional amount of dry hydrate lime (25%) must be added to all formulations during the proportioning stage, or just use lime putty. Note: Portland cement does not experience this volumetric loss when converted to a wet paste during mixing.
Phillips, Morgan, A Source of Confusion about Mortar Formulas, APT Bulletin 1993 http://www.jstor.org/pss/1504465
Most people don’t realize that lime particles are said to be some 500 times smaller than portland cement particles. This might explain, in part, why some lime mortar applications for repointing get so messy with mortar on the faces of the stonework – and yes, very difficult to remove especially the longer the lime mortar sits on the stone. The key in delivering a clean project, one that needs minimal cleaning (just with a small brush and water at the edges of the stone) is water content of the repointing mortar when being applied.
The consistency should be like that of stiff compacted brown sugar like you find in the kitchen cabinet. Yep, just like that. The feeling, the moisture content, and the compaction power. Mortar made to this consistency will not stick to the surfaces of the stonework and cannot be dragged along the top causing a stain from the hawk being pressed against the wall. You get a cleaner wall and the chances of shrinkage cracks are reduced as the mortar cures.
But moisture is important when repointing a wall. Bond strength is delivered during the application when a thoroughly soaked wall (with water) is allowed to partially dry-out and become surface-saturated-dry or (SSD). The SSD condition gives the dry mortar a bond potential with the advancement of each masons pressurized push against the material to the back of the joint. This is why it is so important that the masons repointing tool be sized to fit within the joint to allow for this compression.
I have seen a trend in recent years to rely on washing down the repointed walls with a light solution of an acid-based cleaner to remove the mortar stains from the stone surfaces. Problem is that the cleaner also cleans the mortar and dissolves the binder paste from the surfaces. While some in the industry call this aging the mortar, because it exposes the aggregate and gives the appearance of an old mortar joint. Well, you would get that appearance anyway if you waited 10 years as the lime paste naturally wears off the surface of the aggregate particles.
So, in fact, what you are doing in washing the wall down is giving the customer a used wall – a clean wall, but a wall that has been exposed to accelerated weathering is how I look at it. I figure you rip off at least 10-15 years of life cycle performance from the face of a mortar joint by washing it down with an acid-based cleaner. Seems the evidence is clear that the lime mortars do not withstand a cleaning as well as portland cement-based mortar mixtures. What makes things much worse is that lime mortar is very absorbent to water by its natural ability to transfer water in and out through evaporation which often causes the cleaners to penetrate deeper into the joint surface weakening the material even further.
The story I tell in my masonry seminars is a fun one to illustrate the point. It would be like selling someone a brand new set of tires for their truck and make them pay full price for them, but just as they are ready to drive away, you tell them, “Let me use your tires for say 20,000 miles first, then I will give them back to you” – essentially selling them used tires for the price of brand new ones. Don’t sell used lime mortar.
I attended a social networking gathering at my wife’s college last week. The university has an architecture program with an emphasis on sustainability. I was introduced to one of the students a “MArch Candidate” it said on his business card. I mentioned I was involved with historic preservation of traditional architecture and his eyes lit up.
His young energy filled his mouth with words of interest, but I truly knew he had not a clue what I did for a living. We exchanged pleasantries and he mentioned sustainability as one of his schools focal points, and his as well. I discussed my specialty in Division 4, Historic Masonry, and followed it with the statement that preserving architecture is the ultimate sustainability.
When you stop and think about it for a moment, it really is something.
The brick are already fired, no need for fuel or manpower to extract the clay from the earth – already done! Same goes for the stone – already quarried to size, and transported to the site – lifted into place. The mortar ingredients have already been located, sifted, fired, mixed, and installed between the units.
All the collective energy and labor effort in Division 4 has been paid for and is waiting to provide more life-cycle performance to the next generation – for perhaps another hundred years. With the right preservation plan for its reuse you have sustainability at its finest.