Posts Tagged lime putty

Preservation – Looking Back to Look Forward – Workmanship of the Mason

US Treasury Department Building under construction, ca. 1867 - Image courtesy of the Library of Congress, Washington DC

US Treasury Department Building under construction, ca. 1867 – Image courtesy of the Library of Congress, Washington DC

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.

Lime Mortar Training Workshop at the U.S. Capitol, Washington, DC 1997. Image Courtesy of the NPS.

Lime Mortar Training Workshop at the U.S. Capitol, Washington, DC 1997. Image Courtesy of the NPS.

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.

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The Lime Cycle

Lime has been used for thousands of years for building construction as an ingredient in mortar and plasters and limewash. The conversion process by which the material claims its name is from the lime cycle. It is described in most books as a clock face with the corresponding chemical reactions and changes to limestone that take place as it goes through the various cycles.

The Lime Cycle

At the noon position on the clock face we have limestone [calcium carbonate – CaCO3]. As we move around the clock-face toward the three o’clock position we introduce heat. The heat needed to convert limestone to quicklime [calcium oxide – CaO] is 1,650F.  At that temperature the CO2 is driven off, water is vaporized into a gas at a much earlier stage in the firing process at 212F. From the three o’clock position moving toward the six o’clock position we introduce water to the quicklime.

This converts the quicklime into lime putty while giving off an exothermic reaction causing the water to boil in a process called lime slaking. The lime putty [calcium hydroxide – Ca(OH)2] settles down into a consistency of thick Philadelphia cream cheese before its ready for use. The quicklime naturally takes the amount of water it needs and drains off the rest, so in a sense you over soak the quicklime during slaking and the material finds its natural balance as it settles down into a putty under the water – a process that generally takes 60 to 90 days to complete if left undisturbed.

Moving now from the six o’clock position to the nine o’clock position we introduce sand, and mix the lime mortar or plaster into a cohesive mixture usually in a volumetric ratio of 1 part lime putty to 2.5 parts sand. We end up at the nine o’clock position with our mixture ready for installation.

From the nine o’clock position back to the noon position we introduce water to the walls [by spray misting] in a series of wetting and drying cycles to encourage carbonation.  Carbonation is defined as the process by which lime cures – or converts, back to limestone from which it originated. We suggest a minimum of nine (9) wetting and drying cycles to initiate this process after installation. And that’s it!  That is the process of the Lime Cycle. We take limestone apart using fire, mix it back up with water and sand and we have lime-stone mortar in the end – a very durable long-lasting material.

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Moisture – Part Four, Solutions

Part of the solution to the problem of moisture migration is allowing the water to have its way. In above grade walls, that means letting it go through the wall, then redirecting it through flashing and weep holes if possible, and most importantly, using a breathable mortar that is more porous than the brick or stone.

Below grade, keep water from resting on the outside of the foundation walls in saturated soil conditions. Create a drainage system, a way for the water to move away from the foundation, perhaps installing perforated foundation tile at the base footing of the wall with gravel fill. Again, check gutters and downspouts to ensure they are clean and take water away from the wall, extending downspouts at least three feet past the elbow at grade level is a good idea. Grade the soil and pavement materials around the building to encourage water runoff and avoid collecting and pooling near walls.

A digital moisture meter in use

Detecting trouble in advance – The use of a moisture meter can sometimes be helpful in determining a baseline for acceptable moisture content in a historic masonry walls. Because not all masonry walls are created or built equally, all have varying levels of moisture depending on conditions. What is important in establishing a baseline is looking for the wall sections that are performing well.  In these areas, take readings to compare to areas with deteriorating brick or stone. This will put you on a specific path toward understanding what to expect in the future.

Also consider choosing breathable mortar materials like lime putty or hydraulic lime blended with coarse aggregate particles – often the vary material that has turned to dust over the past 100 years. Do not try to make it stronger or better. Just match the old lime mortar and move onto the next project. If the original historic mortar has turned into dust or is falling out of the wall, it is likely a lime mortar. It has done the hard work of absorbing more water than the brick over and over again and now needs replacement. The brick or stone is generally preserved in these cases.

The new lime mortar replacement mixture should match the old mortar and perform as the old mortar did – it to will turn to dust and fall out of the wall in the next hundred years, giving the next generation something to fix.

Lime Putty Suppliers in the US:

U.S. Heritage Group, Inc.

Virginia Lime Works

Hydraulic Lime Suppliers in the US:

Limeworks.us

U.S. Heritage Group, Inc.

Virginia Lime Works

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The Lime Revival

J. Speweik during on-site masonry inspection

As a young boy growing up in a family of stone masons mixing mortar was like brushing my teeth…I did it every day, at least during the summer months when school was out. Who would have thought that in the age of technology, speed and convenience that my great great grandfather’s 1846 mortar formulation would return. The trend seems to be one that is sweeping across Scandinavia, Europe and Canada as architects and heritage masons work together to preserve their country’s historic masonry properties built hundreds and often thousands of years ago.  They call it the “Lime Revival” It’s been 30 years for Sweden, 20 years for England, 10 years for Canada….its America’s turn now.

The oldest archaeological sites in the world are, of course, masonry. As early as 2450 B.C., masons began using lime and sand for mortar. Lime is made from limestone (calcium carbonate) which has been heated to temperatures exceeding 1,650F where the heat drives off the carbon dioxide and water turning the limestone into quicklime (calcium oxide). Traditionally this quicklime (sometimes called lump lime or hot lime) was delivered fresh to construction sites or made on-site in a temporary kiln just for the job. The quicklime was mixed with damp sand and stacked up into piles for slaking into a hydrate powder (calcium hydroxide) and run through a screen or the quicklime was combined with water in the ground, formed into a putty (also calcium hydroxide), and mixed with the sand at a later time depending on the project needs. Either way, the mixtures were left to mature or rest for a time before use, due to the expansion of the lime particles during slaking.

The lime was generally mixed with local sand in a ratio of 1 part lime putty to 3 parts sand by volume. Other ingredients like crushed brick, clay, lamp black, and natural cement were sometimes found in smaller quantities before 1870; however, the basic lime putty/quicklime sand mortar formulation has remained unchanged for centuries.

Portland cement was first manufactured in America in 1871, but did not become truly widespread until the 20th century. As late as 1883 there were only three portland manufacturing plants in the U.S. Up until the turn of the last century portland cement was considered an additive, or “minor ingredient” to help accelerate mortar set time. By the 1930s, most masons were using equal parts of portland cement and lime putty or quicklime. Thus, masonry structures built between 1871 and 1930 might be pure lime and sand mixes or a wide range of lime and portland combinations.

What we do know about lime, and the reason for its come-back, is its incredible performance characteristics, and versatility as a time-tested building material – and not just as a masonry mortar either, but also as paint, (limewash/whitewash) exterior stucco/render, and interior plaster as well. Lime, when properly combined with clean, sharp, well graded sand can perform for many centuries in masonry applications. Lime has the ability to handle water without trapping it within a wall structure. It is breathable, flexible, obtains high bond strength to masonry units, it is truly sustainable (less energy is required to heat a ton of lime as compared to a ton of cement) and it has autogenious healing capabilities, often referred to as “self-healing” where hairline cracks do develop over time water combines with the lime again to re-knit the cracks back together. Limes durability comes through a process of what’s called carbonation. Carbonation is a process by which lime turns back to limestone by reabsorbing the CO2 back from the atmosphere though wetting and drying cycles. You can say that the material interacts with nature on a daily basis.

Portland cement mortar "Cover-up"

As portland cement became more widely used many lime sand mortars were being “covered-up” during repair projects. Exterior masonry buildings suffered badly from hard portland cement mortars (1940s until today) which did not accommodate for movement or stresses within the wall systems, and as a result, many historic brick and stone units got damaged by this un-sacrificial material. When cracks did occur, in the portland cement mortars, water would migrate into the wall cavities and not be able to escape or evaporate back out as they once had done with the lime sand combination mortars.

But times are changing. We are seeing signs of the “Lime Revival” hitting the shores of the United States. Mortar manufacturing companies are now offering lime mixes now for restoration and a few specialty companies offer traditional lime putty, quicklime and imported hydraulic lime for sale.

Lime mortar materials, that I am currently aware of, are available from the following U.S. companies listed in alphabetical order for your convenience.  Be sure to ask questions about each of the company’s offerings, as they differ. Some still use portland cement in their lime mortars. It’s best to know what you need first – then go out and find a supplier that can meet that need.

Cathedral Stone Products

Edison Coatings

LimeWorks.us

SpecMix

Transmineral

U.S. Heritage Group

Virginia Lime Works

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Hydrate Lime vs Lime Putty – Mixing

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).

Mixing a 1:3:12 Cement/Lime Putty Mortar

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

 

 

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Lime-sand Mortar, Winter Limitations

Lime putty mortar ready to be installed

I often get asked this time of year, “How late in the construction season can we work with lime-sand mortars?” Well the quick and fast answer is 45 days before the first hard frost. Which means you should have your projects wrapping up by the end of October at the latest just to be safe. The reason for this safe period (as suggested by lime mortar manufacturers) is because of the way lime-sand mortars initially cure, by carbonation – absorbing CO2 back into the material through wetting and drying cycles. Most specifications call for a minimum of nine (9) wetting and drying cycles of misting the walls down with generous amounts of water after installation and allowing them to dry out naturally – drawing in the CO2 from the evaporation of the water. Obviously, this wet-curing process can become problematic during freezing temperatures.

The Brick Industry Association, March 1992, Technical Note 1 states, “Mortar which freezes is not as weather-resistant or as watertight as a mortar that has not been frozen.  Furthermore, significant reductions in compressive and bond strength may occur. Mortar having a water content over 6 to 8 percent of the total volume will experience disruptive expansive forces if frozen due to the increase in volume of water when it is converted to ice. Thus, the bond between the unit and the mortar may be damaged or destroyed.”

But what if your schedule backs you up against old man winter and you have no choice but to work into November? Don’t lose heart. We carried out some testing 8 years ago on a project in Chicago [Lime Mortars, Two Recent Case Studies, Ed A. Gerns and Joshua Freedland] to find out how late in the season you could repoint a building using lime-sand mortars. Trials were conducted at various times in the fall and early winter at approximately six week intervals. The last installation occurred 48 hours before the first frost on November 23, 2003. Observations during installation, following initial curing, and periodically through the winter and following year were noted. The high-calcium lime putty and sand mortar showed no signs of shrinkage cracks, the bond between the mortar and brick units was well-adhered, and no erosion or cyclic freeze-thaw damage was observed. We were working with butter joint brickwork of 1/8 inch mortar joints.

To supplement the insitu testing, limited concurrent laboratory testing was conducted to evaluate the depth of carbonation and the impact of freezing temperatures had on the depth and rate of carbonation of the lime. Two inch mortar cubes were made from the same mortar formulation (1:2.5) – no additional water was added.  The mortar cubes (eight sets) each went under freezing temperatures once for a four-hour duration at various times after initial mixing. The exposure to freezing temperatures (10F) was established at 24 hrs; 48hrs; 72hrs; 96hrs; 1 week and 2 weeks. The mortar cubes were then broken at various times and the depth of carbonation was measured using a phenolthalein solution as an indicator.

After 2 weeks, the depth of carbonation suggested that mortar cubes that were exposed to a freezing temperature for a limited duration during the first week had less depth of carbonation than the cubes that did not experience any freezing temperatures. After three weeks, however, this difference was no longer observable. All mortar cubes seemed to equalize after three weeks. Interesting. The success of this trial may be a result of the forgiving nature of lime-sand mortars, the low water content of the repointing mortar, and the narrow joint width of this particular project.

This paper was presented at the 2005 International Building Lime Symposium in Orlando, Florida. Proceedings are available on CD (ISBN 0-9767621-0-2).  The CD includes 39 papers by authors from 10 countries.  Also, included are several important historical documents related to building lime–some as old as 1920.

The conference proceedings are available for $25 at: http://www.lime.org/documents/publications/free_downloads/summary-ibls-2005.pdf

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Measuring and Mixing Historic Mortar

Various Sands for Comparision / Matching Historic Mortar

The traditional volume mix design of 1 part lime putty to 3 parts sand may be insidious to follow straight up without more details. First, mix designs historically used quicklime as the 1 part of lime mixed to the 3 parts of sand by volume. Quicklime when it is slaked with water will increase volumetrically 70-100 percent – or basically double its size. This fact would reduce the sand content closer to that of a 1 part lime to 1.5 parts sand – a much sticker richer mix design.

Secondly, sand must be measured in a damp loose condition according to ASTM C270 when mixing mortar. Dried sand will bulk up to 30 percent and grow volumetrically by the addition of a small amount of water. This can send your mortar mix designs at the construction site off the specified requirements.

I recommend everyone take a moment to read Gerard Lynch’s article on the subject it is well done. http://www.buildingconservation.com/articles/mythmix/mythmix.htm

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Lime Putty Mortar – Buckshot

Lime Mortar Buckshot - the Wrong Way to Mix

Let me save you some time and trouble if you are considering specifying lime putty (ASTM C1489-01) for your next historic masonry restoration project. Forget about the standard way of mixing mortar with a gas-powered paddle mixer or drum type machine used in new masonry construction. These machines require the mortar ingredients to have a high rate of flow by adding enough water into the mixer to keep everything moving and mixing thoroughly. Not so with lime putty. This material is generally 50 percent water and 50 percent solid (looks like thick cream cheese) and requires a mixer that provides pressure or a kneading action to evenly incorporate the sand particles into the material.

Mixing lime putty and sand together works well when mixed by hand with a mortar hoe and shovel as you can place pressure into the mix by pressing down during the process. Ramming rods made from wood with handles also work well to beat the mortar into submission forcing the sand particles into the lime putty.

What is interesting about mixing lime putty mortar, if you have never had the pleasure to do so, is that it requires no additional water once properly mixed. There is enough water in the lime putty to create a good workable mixture that can be used for repointing. For years we have used a vertical shaft mixer that whips the material into form from the outside-in once all the ingredients are in the shaft mixer. So whatever you decide to do on that next historic masonry restoration project, if it involves lime putty, be ready for some good-old-fashion hand mixing or get ready for some buckshot of lime putty balls coated with sand!

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Whitewashing / Limewashing

Whitewashing has been used for many years to cover and protect historic masonry, even before it was historic! A whitewashing application involves mixing lime putty with water in a ratio of 1:5 then vigorously stirring the material until the lime putty fully dissolves in the water. Colors can be added from earth pigments but most material was used white – thus the name. The lime (calcium hydroxide) sets slowly by absorbing carbon dioxide from the air. The chemical reaction that occurs produces crystals of calcite. These crystals are unusual because they have a double reflective index: light entering each crystal is reflected back in duplicate. This results in a wonderful surface glow that is characteristic of whitewashed surfaces and is not found in modern paint products or imitation coatings.

The application of whitewash acts more like an absorptive stain. It is not a coating so it will not peel-off. After it hardens whitewash remains vapor permeable and will not trap moisture in the wall. One of the attractive attributes is that it gradually wears off the surface of the wall over time leaving a very pleasant uneven aged look.

Many architects and designers seek this look but have had challenges because they have been using the wrong products, such as paint, to achieve the effect. If it is a traditional look you want to specify than its best to go back with the traditional material that will get you there.

The key; however, is in thinly applied coats. This facilitates the carbonation process of curing and prevents crazing and cracking. It is helpful to specify onsite application training – as most painting contractors will treat the product like paint and attempt to get the surfaces coated in paint-thickness applications. Most raw masonry surfaces require 3 to 5 applications of whitewash, then after that, just a single coat will do the trick to freshen things up later.

Additional reading: http://www.slideshare.net/speweikpreservation/speweik-limewash-returns-2000

http://ncptt.nps.gov/2011/study-on-the-durability-of-traditional-and-modified-limewash/

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