A Green Portland Cement Alternative, FAQ Friday with Randy Ruth

You might ask yourself… How is Natural Hydraulic Lime (NHL) a green building material? The simple answer would be that it releases about 80% less CO₂, pound for pound when compared to Ordinary Portland Cement (OPC) during the manufacturing process. But why is this so? Well that requires a bit of understanding on the manufacturing of the two very different products.

Both NHL and OPC are made from limestone, although not necessarily the same kinds of stone and are fired in a kiln. NHL is produced in Vertical shaft kilns, which is like a big chimney, with natural gas or clean coal at a low temperature. While OPC is burned in a rotary kiln fired at nearly 2,500 F. The amount fuel used to maintain such a high temperature is by far greater than the relatively low firing temperature of NHL.  Often hazardous waste is used as a fuel, which can emit toxins into the atmosphere. During either process CO₂ is driven off into the atmosphere. Even though NHL production drives off less CO₂, the benefits don’t stop there.

When the NHL is ready to be mixed as a mortar right out of the bag, it’s hungry. NHL wants the CO₂ that was pumped into the atmosphere back all for its self, in its natural process to turn back into a limestone. As different grades of NHL are produced their whiteness and density change. On a scale from lightest to heaviest and from whiteness to grayness, NHL 2 is Light and white while OPC in heavy and grey. Since mortar is mixed by volume in the field, less lime is used per pound to make up the same volume of mortar using OPC.

-LimeWorks.us (Linked-in : Blog : Facebook : Twitter)

How Lime Mortar Traditionally Got Its Color and How We Can Replicate This Today, FAQ Friday with Randy Ruth

Seven factors that can affect the color of lime mortar in no particular order of significance, Lime, aggregate, pigment, water content, rate of absorption, original surface texture and erosion.

By its self, the color spectrum of lime can vary from bright white, light grey, slight pink or ochre colors. This color is dependent on a few factors such as the original stones chemical makeup and burning temperature. When an appropriate limestone is thoroughly burned (calcined) at a particular temperature to produce hydraulic or non-hydraulic quicklime and then hydrated to produce either a lime putty or dry lime hydrate, the result will be a white or off-white color. The first factor affecting the whiteness index of the lime will vary depending on the raw mineral impurities in the limestone. A limestone with a higher calcium content with all other factors aside will produce a whiter hydrated lime. If that same limestone is burned at a slightly higher temperature, the result will be a slightly grayer hydrated lime. Although, lime plays a role in the final color of a mortar, its significance today, when replicating a mortar joint is minimal, often due to the lack of availability or technical characteristics like Hydraulicity.

Aggregate has a huge effect on the color of lime mortar. Historically aggregate for masonry mortar would be sourced from either local sand beds, found near creeks or rivers, or from the trimmings of stone on site and possibly brick pieces or dust as a pozzolanic additive. The larger screenings of the aggregate play a role in the overall tone of the final mortar color but it is the fines that do most of the work. The smallest particles in the aggregate AKA fines will give the biggest impact on the final color. Brick dust, limekiln dust and clay impurities are pozzolanic fines that can be found accidentally and at times intentionally accompanying the aggregate. Today these impurities are almost never allowed into a replicate mortar mix, as the resulting technical data from such a mix design is often cost/time prohibitive for a project even if historically appropriate. As a result powdered pigments are often used today to achieve a particular mortar color.

Just because pigments are predominantly used today in mortar mix designs, doesn’t mean that they weren’t used over 100 years ago. Colored mortar is an important design element in any building of today and yesteryear. The types of pigments used in mortars have not changed all that much in past few hundred years. Iron oxide, carbon black, and natural ochre’s hold a solid footing in the industry today, each presenting their own limitations.

It has been proven that carbon blacks can fade dramatically over a 30 year period in masonry mortar. Even though their tinting strength is very good, if not controlled carefully  shades of grey can be very difficult to achieve. Natural ochre’s can produce wonderful colors and be very accurate when making accurate replicate mortars. The problem is in their tinting strength, and consistency in production on a large-scale. It may take above a 10% dosage of natural pigment to achieve the same color in a mortar using iron oxide pigments conforming to ASTM C979. Because of their durability, tinting strength and quality in production, iron oxides have been deemed the best pigment for coloring mortar on a large-scale.

Even when using appropriate pigments at the correct concentration, water content in a mortar plays a big role in determining final color. Using the same exact mix in two batches and varying the water content by 10% will produce a significant change in color. From experience, I have noted that this problem is most evident when trying to achieve a red colored mortar. Light grey’s can also be problematic but are less evident and are usually deemed acceptable. That is why it important to measure all ingredients in a mix carefully to ensure consistency from batch to batch.

The practice of mixing mortars consistently should carry over to pre-dampening of masonry units. By pre-dampening consistently as possible, the rate of absorption is controlled. This is a good practice just so mortar will not reach a flash set, and to control curing of the mortar which plays a role in the final color.

There is some debate on how a replicated mortar should look when not replacing all the mortar. Should it look new, with a smooth surface that stands out because of the way light reflects off two different surface textures? Alternatively, should it blend in with adjacent mortar joints? Personality, I believe in the latter. If a new mortar is inherently the same color at its core as the old historic mortar, than even though a slicked smooth replacement mortar will eventually blend in it can still distract the eye. A good repair for just about anything should be as seamless as possible. Besides, won’t a different texture erode differently, resulting in the continuation of a miss match over time?

This brings me to erosion in mortar. As a mortar erodes, the color of the aggregate begins to come through. This color can sometimes throw off the human eyes perception of what is the color to be achieved when color matching. Someone explained this to me so well once that I must share. He had asked a room full of people what the color of foam on the head of a beer is. All replied white in color. We all got it wrong. The answer is amber like the color of the beer. This is because of the way light is reflected back to the human eye off a larger Surface area. Now that is in extreme case of a dark color turning lighter but the principle is still applicable to mortar. However, in most cases the rougher the color the darker a mortar is, and depending on who well the color of the sand is matched, you may just get a replacement mortar that will be seamless for generations.

-LimeWorks.us (Linked-in : Blog : Facebook : Twitter)

Limelight on historic Guanajuato, Mexico

We are thankful for your work as an associate in green building and historic building conservation. Every six weeks we plan to focus the limelight on a story that we think will strengthen the collective resolve to remain strong advocates of resource conservation. A snapshot video or “Spark Segment”, as we call it, is how we will put the limelight on highly skilled craftspeople, sharp engineers or creative designing architects and builders. A spark segment will celebrate their current work or the legacy of great works they’ve left behind. With each installment we hope to capture the essence of “movers and shakers”, (people, places and objects), that inspire us to continue pressing forward. We remain faithfully yours as advocates in this most sacred work.

This segment features the city of Guanajuato Mexico which brings us a sampling of authentic Moorish detailing found in its natural surround with an intact and rich cultural element. The inspiration to put the limelight on this region comes especially from the passion that is evident in the hearts of the people of this culture which has spilled out into their built environment. This is just one example of vibrant lime colorwashes and the conservation of regional heritage by people who care. Let’s continue to be that type of conservator in the areas where we exhibit our influence as professionals.

-LimeWorks.us (Linked-in : Blog : Facebook : Twitter)

Lancaster Central Market Wins Pennsylvania Historic Preservation Award using Natural Hydraulic Lime

Congratulations to the city of Lancaster and Hammel Associates Architects, LLC. They were recently awarded for the restoration of the Lancaster Central Market in Lancaster, PA. Located in the middle of downtown, this space has been used as a market since 1730 and is said to be the oldest continuously operating farmers market in the country. The market structure was designed by architect James Warner and constructed in 1889 of locally produced red brick on top of a brownstone base. The market was named one of America’s top ten “Great Public Spaces in America” by the American Planning Association in 2009.

Many efforts were made in the recent rehabilitation project to restore the market’s elements including the original windows and doors. The damaged bricks were replaced and the building was repointed with Natural Hydraulic Lime 3.5 and deGruchy’s Ecologic® Mortar provided by LimeWorks.us  as a complementary mortar to the original lime mortar of 1889.

These appropriate historic restoration techniques worked to bring the market back to its original glory for the enjoyment by generations to come.

Using Natural Hydraulic Lime in cold weather, FAQ Friday with Randy Ruth

As fall encroaches upon us with its cold weather, a question that is going to be popping up with more frequency is… Is it too cold to start or finish my project with NHL?

This maybe one the most difficult questions to answer, where the wrong answer can result in a lot of lost time and damage. The simple and safest answer is, do not perform work with NHL when temperatures will fall below 40 degrees Fahrenheit (including wind chill) for at minimum 7 days after placement of the mortar. Even following this model answer can result in frost damage of the mortar in some cases. So what is an applicator to do, to ensure that their work will last a reasonable amount of time? Well, care, caution attention to detail and patience is the answer.

If you can wait until spring to complete the project then you probably should to play it safe. If however, you absolutely need to complete the project before winter and do not mind playing with fire,  then tenting and heating the scaffolding is an option. Tenting and heating can cost a lot of extra money in labor and fuel, so obviously make sure that there is enough money budgeted aside to warrant this approach.

By completely encasing the scaffolding envelope with heavy-duty plastic and being sure to affix the uppermost part of the plastic to either the roof or its eve, one can create a tight enclosed space for heating. When using a heater make sure that it is in a safe place and slightly raised off the ground. You should refer to any local building codes to make sure that you are in compliance and most importantly safe.

Of course, good masonry practices should not be skipped over just because the work is tented in and heated. Damp curing with burlap is still recommended and when repointing work is being executed good compaction of the mortar against the background mortar is still a must.

There are a few other tricks available to the applicator that can help prevent frost damage. One is the use of air-entrainment in the mortar. Careful dosing of an air-entrainer can help but not eliminate frost damage due to improper curing practices. Adding air-entrainment must be done with caution, as too much air in a mix will make the mortar weak and friable. When using proprietary admixtures, proper testing should be conducted to make sure that there are no adverse side effects .

Lowering the water content of the mix and increasing mixing time will help reduce the amount of water available to freeze without sacrificing too much workability. The use of warm mixing water, preheated sand as well as preheating the masonry units will help slow the development of frost. Winter accelerators associated with working with Portland cement mixes should not be used, such as calcium chloride or any nitrates. Depending on the properties of the surrounding masonry units NHL 5 can be appropriate to use in a masonry mortar to help withstand frost, due to its faster setting time.

When in doubt about working in possibly freezing conditions or allowing recently completed work to be exposed to freezing temperatures, you should probably trust your gut and call it a season. Dancing with the weather can be costly and should be avoided.

-LimeWorks.us (Linked-in : Blog : Facebook : Twitter)

One quick question on Natural Hydraulic Lime, FAQ Friday with Randy Ruth

Fall has arrived, this morning it was in the 40s! Randy has quick answer today in his FAQ entry…

• Q: Does your Ecologic mortar product contain just sand and lime pre-mixed (what are the major contents) with no cement and all I would need to do is to add water
• A:  Ecologic® Mortar is a blend of 1 part Natural Hydraulic Lime 3.5 with 2.5 parts sand meting ASTM C-144 and iron oxide pigments when appropriate in our 9 stock colors. When you want to begin repointing the stone mortar joints after proper preparation of the wall, all you do is add water to the powdered contents of the bag in either a 5-gallon pail or mortar mixer and mix for about 10 minutes, then get to work.

Happy Birthday Randy Ruth, and FAQ Friday!

Send Randy some love and give him a birthday shout out when you repost his latest blog entry on some of the differences between repointing with Natural Hydraulic Lime (NHL) mortars vs. cement based mortars.

Q: Is pointing with lime different from pointing with cement? I’ve done work with cement but I want to know what the differences are for application and general use for repointing my old house?

A: When you refer to pointing, I am thinking you are referring to repointing mortar joints. As with any masonry project, proper attention to preparation of the substrate is critical. Always follow proper preparation guidelines regardless of the mortar being used.

If you compare the application process of repointing mortar joints with lime-based mortars to cement based mortars, the only real difference is workability.

Lime mortars tend to have better workability than their cement counterparts do. This is because lime is used to add plasticity to modern cement mortars and thus, when you omit the cement you have the greatest workability. However not all lime mortars can be treated equally when it comes to their aftercare during the initial curing process. Like cement-based mortars, there are different grades of lime for different applications, with different characteristics.

Although there are many different types of limes used around the world, I will only address the four most common from softest and slowest setting to hardest and quickest setting. starting with High calcium lime putty, (Natural Hydraulic Limes)NHL 2, NHL 3.5 and NHL 5.

High calcium lime putty is the softest and slowest setting of the lime choices. Proper attention to curing procedures must be adhered to allow it to set properly, this may take six weeks. Lime putty based mortar has its place in the world, where trained professionals should be the applicators to ensure work is executed in way were the margin for error is limited.

Different grades of Natural Hydraulic Lime are followed by a number designation that indicates the minimum compressive strength at 28 days with a particular amount of sand in Newton’s per millimeter squared. The reason for this classification is that there are no Natural Hydraulic Limes currently produced in the United States and must be imported from where the metric system is used and there have been established standard for a number of years on NHL’s, primarily in Europe.

As said before, the lower the number designation for NHL’s the slower setting and softer that type is. So, what does all this mean to you the mason or adventurous DIY homeowner?

Well if you have a conservator mindset then matching the new mortar as closely as possible to the old mortar in color, texture and physical attributes is the end goal. You might want to consult a professional for general advice on what type of mortar to use if you are unsure, after conducting your own research.

In general, for most of the United States NHL 3.5 mixed with local sharp well graded sand, which should meet ASTM C-144 or a pre-blended NHL 3.5 and sand mix can be used for general repointing work of older brick and stone structures. This is because NHL 3.5 has an acceptable initial setting time and more importantly provides good vapor transfer in a wall. This allows repointing work to move along at an acceptable speed while knowing that in most cases moisture is not being trapped in the wall cavity.

Lastly, the difference between cement mortar and lime mortars for repointing is aftercare. Even though cement based mortar should be damp cured it is not always practiced and is not typically the same length of time when dealing with lime.

While working with NHL mortars it is important to allow the mortar to slow cure with high humidity or by misting with water, keeping the recently completed work damp. Although the length of time for aftercare curing of mortar will vary in direct proportion to the particular grade of lime used. Generally, 2-4 days of slow damp curing with either damp burlap misting for repointing work is acceptable. In some cases however, this curing period should be extended.

All about Lime

This is an excerpt from The Stonemason’s Gospel according to Ian Cramb written by Andy deGruchy, an explanation of lime.

Lime

Limestone, the material calcium carbonate, has never changed from its beginning up to and including now. There have always been two classifications, ‘pure’ and ‘impure.’ Today it is classified as pure (high calcium) and two levels of impure lime based on the magnesium content, Dolomitic and Magnesian.

What has changed over the course of time, especially in more recent years, is how the calcium carbonate stones have been prepared by firing them in the kiln to produce quicklime. There is a most simple way of burning limestone in a vertical kiln using wood for fuel and keeping the temperature between 1650F and 2000F and then cooking it slowly over a few days. This has been done for centuries.  The proof that this method of cooking the stone has extreme merit is evidenced by the very old buildings throughout the world which still stand that utilized this method of preparing lime. ‘Lime’ is what limestone is called when it is cooked and slaked to make a putty that is incorporated into making building mortars, plasters and paints. The technical chemistry was unknown to old lime burners and masons. They just knew what worked and kept using the time-honored methods of preparing the lime.

When burned limestone has water reintroduced to it, called slaking, it then blooms into a beautiful white putty-like material. The volume of putty produced is double that of what was once the condensed rock. This ‘lime putty’ will draw carbon dioxide out of the air for a very very long time and slowly convert back closely to a limestone again. Lime putty has its initial set over a six week period by exposure to air. However it will attract carbon dioxide almost to a point of being completely ‘carbon neutral’ over time in regard to the embodied energy first required to produce the lime.  Through lime’s interconnected pores it even knits minor fissures together by moving about some of the not fully burned ‘free lime’ which creates more surface area to draw in the carbon dioxide.

Early masons knew that some limestone deposits produced limes that set quicker and became harder sooner. So, unlike simple air-setting lime putty, hydraulic limes were used throughout the world and in the United States to build with when the impure raw material had reactive silica or certain clays naturally found in the stone. These impurities were cooked along with the calcium carbonate stone. The term ‘hydraulic’ means to set with water and under water. Portland cement is hydraulic lime. The reason it is overall strongly suggested not to be used for masonry building conservation is that the synthetically added materials used to make Portland cement become intensely hydraulic also make the whole lot detrimental by various degrees of incompatibility with original porous building components. Two of those detrimental characteristics are that Portland cement is brittle and does not accommodate movement and secondly it reacts with sulfates. But a great incompatibility and detriment to historic masonry buildings is the increased densification of mortar that consequently occurs with every increment of additional Portland cement added to make the mortar become very hard. Densification does not allow the building to remain ‘breathable’ through the mortar joints but instead allows water to become held back and sometimes trapped into absorptive inner bedding joints. This phenomenon forces the wetting and drying cycles of the building to occur through the porous historic units and this is what greatly contributes to accelerated deterioration of the irreplaceable bricks and stone used to originally build a building.

In Ian’s first book he used and suggested mortar mixes that I and every other mason has typically used. These mixes gauge-in some Portland cement into high-lime (Type S lime) containing mortars. The reason we all did this is because readily available Type S Hydrated Builder’s Lime and cement were what we had to work with prior to the commercial availability of natural hydraulic limes now sold in the US. If Type S lime was blended with sand alone we discovered it would not hold up to the freeze-thaw cycles in northern climates. Why this occurs when nothing has changed about the limestone itself puts the spotlight on the cooking procedures. Too hot and too fast of a burn can cause the limestone to become ‘dead-burned’ and loose its ‘reactive’ nature which allows it to closely convert back to a hard and durable limestone again. A durable mortar made from reactive lime which maintains vapor permeable pores and has a desired malleable nature to accommodate minor building movement is the best for vertical, above grade work. Pure air- setting limes that remain reactive because they are burned at a low temperature can be obtained in the US too. However, due to the six week set time the cost for building with these limes goes up exponentially. So in this book the mortar mixes are more clearly defined from Ian’s first book as being mixes that use a binder of hydraulic lime but not the hydraulic lime that is Portland cement. I hope this helps you in designing appropriate mortar mixes for certain corresponding applications. It is a labor of love and worth understanding in order to realize the greatest long-term service life which can be obtained for repairing a vintage building and its components. I hope my contribution of this knowledge into what makes one lime better than another brings about a higher degree of excellence in the historic building conservation work you endeavor to do.

Sincerely,

Andrew deGruchy

Natural Hydraulic Lime – Creates Old-World finish That is a Perfect Finish Selection for Wood-Fired Ovens, Foundations, and Other Masonry Projects (via The Arch Blog)

Great post about a unique way to use Ecologic® Mortar.

The ARCH, known in part for it’s natural finish options, has recently gained more experience with a Natural Hydraulic Lime finish product that we offer.  Jim Erskine’s masonry experience spans thirty plus years, and as with most masons, his experience … Read More

via The Arch Blog