Article 1: The National Park Service's National Center for Preservation Technology and Training (NCPTT) Podcast interview with Andrew deGruchy - "Historic Uses of Lime Mortar, and Its Continuing Importance Today" (Please allow a few moments for audio to load).


Article 2: Avoiding the Bait and Switch tactics attempting to lure you from using pure Natural Hydraulic Lime (NHL) to using synthetic “Hydraulic Lime” (HL) as a non-cementitious building lime alternative

Advice about locally available (Non-Hydraulic) Hydrated Lime

We don't sell Hydrated Lime because it is locally available in the US. However, lime comes basically in two forms, High Calcium which is pure and then two forms of impure lime which is designated either as Dolomitic or as Magnesian lime. Any of these limes could be processed into Hydrated Lime for building and sold as a "pre-slaked" dry powder - the most commonly used and known lime for building purposes.

Hydrated Lime comes in the powder form, designated as Type N, NA, S or SA, or in a paste form known as Lime Putty. Although it has wonderful physical and aesthetic qualities, Hydrated Lime has very strong limitations in the construction industry. It is used primarily with Portland cement to control the setting time and to add plasticity to mortar. Modern processing procedures for most all Hydrated Lime greatly restricts its use as a sole binder in Lime/sand mortars that will remain unprotected from the elements. An exception would be low-temperature fired High Calcium lime which, being around 98% pure calcium kept chemically intact by low-temperature firing, can be used to make a durable mortar without Portland cement. However this lime is mostly available for the food industry and will still require a six week protected cure time. Hydrated Lime sets only by carbonation in the re-absorption of CO2 and thus, thicknesses are very limited for mortars and plasters. Hydrated Lime alone with sand is not suitable or practical for standard thicknesses of scratch and brown coats in a plaster or stucco. High quality Hydrated Lime will work in most cases as an interior finish coat only requiring additional re-blending during the work.

The application of non-hydraulic lime for mortars and plasters requires very highly skilled labor and special care. This is especially true for quicklime to avoid physical harm from lime burns. Quicklime is the term used when obtaining a burned building lime prior to it being slaked with water or "hydrated." Consequently, these limes become a specialty product with associated complexities and costs.

Advice about synthetically created Hydraulic Lime

Hydraulicity can be given to Hydrated lime by only the addition of ordinary Portland cement or what is called a "pozzolan." The types of pozzolans vary with different performance outcomes for different pozzolans. A warning when introducing a foreign substance to create a pozzolanic hydraulic lime is therefore having immediate or long-range inauspicious consequences.

It is not advised to use hybrid products with unknown and unproven performance results. Hybrid products should be found in real service applications for an adequate time, (years), in order to draw respectable conclusions. The Romans synthetically created Hydraulic Lime when the Natural Hydraulic Lime was not conveniently available to them. However, they never started with processed Dolomitic Type "S" (Double) Hydrated Lime that may be a dead-burned product incapable of standing on its own merits as a sole binder in unprotected external applications. The structures which are currently still in existence in the world, which were built by the Romans, also utilized pozzolans which have stabilized since they have proven what can be expected in a final performance outcome if the pozzolans were used in a similar application starting with a similarly obtained and produced lime. Except for the known outcome of using Portland cement as the pozzolanic agent with Type S Hydrated Limes in modern new building work, it is not advised to use synthetically created hybrid hydraulic lime with no track record for any building of value. This is especially true when the subject is the repair of historic heritage buildings. Any sustainable new structure which is being built with the intent of creating a sustainably durable and long-term service life component should avoid the experimental use of a synthetically created hybrid hydraulic lime.

If one were to add a pozzolan to Hydrated Lime then Portland cement would be favored as a material of choice to make a synthetically created hydraulic lime. This is because Portland cement and Type S Hydrated Lime have a known and understood outcome for making successful modern mortars and stuccos which have been in use over 50 years for many modern applications. When value engineering a synthetically created Hydraulic Lime, Portland cement and Type S Hydrated Lime is a favored approach solely because of the low expense coupled with the familiarity of its use by masons and the known service life found in certain applications.

This is not, however, the case for the repair of vintage buildings and for pursuing lower embodied energy mortars. For the purpose of building sustainably and therefore building "Green" it is advisable to take a scientific approach when designing a mortar. In the final analysis any Hydraulic Lime ordered and utilized on a project should be sure to be the type required to meet all the requirements of the application first and foremost. One must secure in advance all proven, long-term success evidence before carrying out the application. If this due diligence is not adhered to there could be disastrous results for the project built with a hybrid hydraulic lime. Knowing that the St. Astier Natural Hydraulic Lime range has a proven track record that can be relied upon is also a good deterrent to the trial and error approach for mortar being used to build valuable structures.

Undue expense for obtaining a hybrid lime mortar for building is not warranted if the application fails pre-maturely or causes surrounding failure for other building components resulting only in excessive overall building expense without benefit. The initial benefit of using a synthetically created hydraulic lime may be focused on initial energy savings in raw material production. However, the long-term energy loss due to the cost to replace failed materials if a hybrid hydraulic lime fails to work as intended becomes for the owner, the architect and the installers just an expensive and troublesome exercise in futility.



Article 3: Restoration Philosophy Article: 3 Tips for Improving Masonry Repairs
(Being educated helps avoid con-men in the industry)


Article 4:


The Chicago Tribune/Washington Post interviewed Andy deGruchy about lime. Since the answers bring light to exactly what lime is and what makes one lime better than another for making durable mortars the interview is included here.

Highlights from the interview with details about lime and cements used for mortar.
(Modified, with current prices for 2012)

  1. A Sustainable Builder and Historic Masonry Restoration professional should consider using Natural Hydraulic lime which sets with water and can have up to 50-60% free lime content that improves the self-healing characteristics of lime mortar. When using a prepared lime putty that sets with air through carbonation, and does not set with water, consider a high calcium lime which hovers around 95% pure calcium carbonate. This height of purity makes high calcium lime closer to just the sediment of bones, shells and plant ash. The more magnesium found in a limestone deems it "Dolomitic" and finally high enough concentrations deem it "Magnesian" lime. Dolomitic lime may be more readily available for construction but high calcium lime putty is available. If you are going to use lime putty that sets with air it should be produced in a gas-fired vertical kiln at a temperature not exceeding 2000 degrees Fahrenheit. Lime's that contain reactive clays burnt at high temperatures can form tricalcium silicates and tricalcium aluminates, depending on the chemistry of the original stone. Low temperature firing does not allow tricalcium silicates to form. The composition of the stone may still lead to the formation of tricalcium aluminates. This is one of the concerns in using Argillaceous, or "clayey" limestone for making Natural Hydraulic Lime and Natural Cement. The presence of various degrees and types of clays can create unpredictable results from one mix to another as well as sometimes cause five to twenty-minute set times when trying to use Natural Cement as a binder. Natural Cements can also be outrageously costly both in product and outcome. A Pure Siliceous Limestone is one that has reactive silica caught up in the stone without the impurities of clay. When limes have a more gray or ochre color and coarse feel they reveal that impurities and higher burning temperatures may be the reason for this. Knowing the final chemical composition of the lime is very important because an impurity may lead to pre-mature failures of the mortar and adjacent areas to the mortar work in some applications. A producer of any lime putty, Natural Hydraulic Lime or Natural Cement should publish the full chemical composition and burning temperatures of the stone they use. If a product is not naturally occuring then the manufacturer should not call the binder 'Natural' when other additives are included to alter set times and other properties. The Natural Hydraulic Lime we currently sell is St. Astier Natural Hydraulic Lime which is a pure siliceous lime. The cost is approximately $40 per 55 lb bag in 2012. When 2-3 parts of sand are added it will yield a goodly amount of mortar. This is relatively cheap since the expense of a project is labor and scaffold and not the mortar. However, the mortar should give a long service life and while Ordinary Portland cement (OPC) mortars are not characterized as a "Green Building Material", they also are not suitable as a gauged-in binder for making new replacement mortar formulas for mortars originally made from pure lime and sand, if the new mortar is meant to last as long as the original mortar. Prepared high calcium lime putty burned at a low temperature may retail around $125 per five gallon pail in 2012. Due to the height of cost for "Hi-Cal" Lime putty, the Pure Natural Hydraulic Limes we import from St. Astier, France become even more attractive to the buyer at $40/bag which will yield approximately 4-Five gallon pails of mortar when sand is added on site. Ask the manufacturer you are planning to buy lime from to tell you what limestone they use and what the burning temperature is.
  2. If you need a cheaper alternative in repointing an historic building or for building a sustainable structure be sure to know the limitations of mortars containing any Portland cement in the mix.  If a building is subject to movement, a lime mortar will move with the building. Through crystalline bridging, using the free lime content, the lime mortar will autogenously heal those fissures that occur. Portland cement mortars become brittle and do not heal themselves due to their miniscule amount of free-lime remaining as a result of their high burning temperatures. However, even in mixes which have weaker concentrations of Portland cement, (mostly meant to give hydrated lime mortars a synthetically created hydraulic set), do in fact, and in every case contain tricalcium aluminates. This is important because it is possible that tricalcium aluminates can meet with water and the soluble salts present in old buildings to produce a detrimental reaction. This reaction's product is a sulfate attack upon the mortar. If the movement of a building can not be controlled and due to eventual voids in cap stones or fissures that open up on the side of a repointed mortar joint or a crack in stucco that doesn't autogenously heal, then lets water in, a breakdown of the mortar may begin or trapped water in the substrate may occur. The breakdown of mortar containing Portland cement may take as little as three years to start. Repointing and installing stucco containing Portland cement gauged into the "High (Type S hydrated) lime" content mortar may simply be considered a more "temporary" fix when met over friable-type substrates. Temporary meaning 10-35+? years as opposed to the original lime/sand mortars still in service over 100 years throughout the world. Friable meaning "weak, very sandy" type bedding mortars or other friable and punky substrates like strawbale, mud for adobe structures, etc. Once the reaction process starts in mortars containing any Portland cement, they continue and the sulfate attack, also known as the "sulphation of cement" occurs and leads to accelerated failure of the mortar. It also will often create irreversible damage to once sound masonry that swells in freeze-thaw cycles and moves units out of position. So exactly how long a high lime content repointing mortar that had Portland cement gauged in to create a hydraulic set can last varies due to the above aforementioned mix of conditions. Compare the cost of prepared building and pointing mortars, stuccos and paints containing Portland cement with the cost of our imported Natural Hydraulic Lime and make an informed choice of which binder to use. 
  3. Remember that Hydraulic limes are not the same as what is often referred to as "Builder's Type-S Hydrated lime" used in mortars made to lay brick and concrete blocks, etc. Type-S Hydrated lime is used to create plasticity in mortar and control the setting time and is not expected to be the primary binder for any extreme weather exterior application or for structural building without a pozzolan-type material such as what Portland cement is meant to do, (to some degree), when it is added to Type-S hydrated lime. You can not substitute Type-S hydrate for Natural Hydraulic Lime and think you will get the same performance results. My observation is that as historic preservation and sustainable building remains lucrative, manufactures are compelled to offer some form of "Hydraulic Lime." Ask the manufacturer to tell you what final performance characteristics you can expect from their lime and what they used to create a "Hydraulic Lime" if it is not a Natural Hydraulic Lime.
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Andy deGruchy's full original response made to the Chicago Tribune/Washington Post
Interview done by:  Diana L. Strzalka

Is the importance of lime putty understood throughout the construction industry?  Why or  why not?

Yes, mortar mixes that are composed completely of slaked quicklime and sand are known by various groups of people. Some of these people may or may not know of their importance. There are still people alive who know first hand of the material who never were masons but were familiar with its use. These people have now become very old folks if they still remember slaking lime when they were young if they either watched or labored for a then old-timer mason. Others may remember the routine on the farm where the barrel of slaked lime was kept for making whitewash and the process which followed whereby everything got its annual whitewash, from the barn walls to the eye level height of tree trunks that lined the driveway, etc.

Having lime in a mortar mix is completely understood by most all masons. However, the lime that most masons are completely familiar with is bagged hydrated lime. Without the addition of a plasticizer such as hydrated lime, to a mortar mix, the mix is 'dead' on the trowel. Lime adds plasticity, allowing mortar to flow, controls the mortar's setting time and shrinkage. The word "hydrated" is simply the introduction of water to the quicklime, in advance, at a building lime production plant. The process when water is added after burning a limestone is called slaking, as in "slaking one's thirst." The thirsty one here is the burned limestone which had the carbon dioxide driven out of the stone by the heat of kiln firing. This burned stone is called by three names commonly. It is called quicklime, hot lime and lump lime. When the burned limestone, whose composition is mostly the compressed sediment of marine life remains, has water newly reintroduced to it, a volatile exothermic reaction occurs whereby the now cooled stone, which had been previously burned, draws the carbon dioxide from the slaking water back to itself in a chemical reaction. This chemical reaction causes the water bath that the burned limestone is slaked in to boil in approximately two to five minutes.

Slaking quicklime was and still is dangerous and time consuming to perform on a job site. The process of doing the slaking in advance for you, by way of an automatic hydrator, was invented. The automatic hydrator was invented in my home town of Plymouth Meeting, Pennsylvania by two men in the Corson family who owned and operated the Corson Lime Company, and it was patented in 1930. The Corson Lime Company operated from 1860 to 1997.  However, it is along with the advance of making today's pre hydrated lime that the loss of some of the performance properties of the traditionally slow burned, wood or coal fired limestone, which is manually slaked into lime putty, may have also resulted. This lack of performance may be known by every mason who ever tried to use pre-hydrated lime and sand to make a mortar. The strength and durability does not come up to that of the best traditionally made historic lime mortars. What masons may not know is that a loss in the reactive properties of lime may be happening because of the higher temperatures that limestone is being burned at today in modern production facilities.

This is the part that many masons and historic restoration specification writers don't seem to know. When this convenient, packaged, hydrated lime material was produced for the building industry it was intended to be readily available in a bagged form so that the plasticity and other properties first mentioned could be added to a mortar mix without the need for the lime to become the primary cementing material. So, no one seemed to miss certain performance properties that the old slow burned wood-fired lime putty had since they were probably more fascinated with what a new union of materials could now do. Portland cement started being made commercially in the 1870's in the Lehigh Valley, nearer to where I now live. Lime as the primary binder faded from use in the United States slowly from the 1870's, when Portland cement began being looked at as the primary binder or cementing material in a mortar mix. Portland cement became even more popular as the mainstream binder in masonry when its bagged contents could be matched with the newly bagged pre-hydrated lime. I use the term "bagged" to mean "packaged" even though "barrels and sacks" may have been the correct terminology back then.  Portland cement mortars had strength properties which could be made in great excess of lime putty mortars and these new mixes had fast setting abilities so that more work could be done more quickly.

Unfortunately even though this bigger and faster approach gave us many of the modern construction marvels, not all this bigger, stronger, faster mentality is beneficial to repairing historic structures. Most historical buildings had bedding and pointing mortar made in the old fashioned and time proven method of using slow, lower temperature fired limestone. Masons in all ages past may not have known these truths but knew that certain ways of making mortar worked. Failures in anything cause people to make a change. I sought out to understand as much as I could, even though I am not a chemist but just a ordinary bricklayer, in the attempt to pursue excellence and do my job better.

More on Lime and Lime burning

There are only three kinds of lime in the world:  Dolomitic, Magnesium and High Calcium. Dolomite is a mineral consisting of a calcium magnesium carbonate. Magnesium lime is just Dolomitic limestone with a higher Magnesium content to deem it High Magnesium or "Magnesium lime." High Calcium is the purest form of calcium carbonate, about 95%, just bones, shells, plant ashes with fewer other elements which deem it "High Calcium."

If I am making mortar, I am going to try to choose high calcium lime over the others because I believe that the more the limestone tips toward the magnesium side, the harder it is to manually slake. The burned high calcium limestone will now follow through with what is called the "lime cycle" whereby one starts with limestone, burns the stone to push off the carbon dioxide, reintroduces carbon dioxide in the process of adding water during slaking and therefore causes carbonation in which the lime, the now called calcium hydroxide, is turning back into calcium carbonate or limestone. You may think that this is a lot of trouble to make mortar! The reason it is worth the trouble is that good lime mortars that were used to build with throughout the majority of all building history can absorb water and also allow it to evaporate from the building via the joints and not the brick or stone.  Also, a crystalline bridging phenomenon occurs when movement happens in a wall and whereby good reactive lime uses the carbon dioxide that the lime is continually taking from exposure to water vapor and air to bridge or close minor fissures making it the ultimate flex material in a massive masonry building.

The issue of "good reactive lime" and its relation to low temperature firing is a 'hot' issue in itself. Burning a limestone disassociates from the stone the water found in the stone. The stone starts out as a calcium carbonate rock and ends up being a calcium oxide or quicklime lump. So, after burning, the calcium carbonate stone which became a calcium oxide stone, the weight will now be about half as much because of the lack of water content which was driven off.

Since I know that in most cases I would prefer to use high calcium limestone for making lime putty, the question remains about which method of kiln firing will I choose. Like baking a cake, you can underburn or overburn but you want it "just right." Just right for lime which is intended to be used as the principle binder in a mortar mix, is a lime burning that creates the most reactive form of quicklime. The old wood-fired kiln may only reach temperatures of 1650 degrees Fahrenheit because the steam produced from the water in the wood keep the fire cooler. However, it also happens that the water in the wood aids in keeping the water's carbon dioxide pressure low enough so it can diffuse through the lump of lime at a slow enough rate to make it "just right" in reactivity. High heat may close the pore structure of the stone, not letting this happen optimally. A modern lime burning kiln is not a crematorium, but if you think of an example like a crematorium, and how if one were to increase heat immensely, a material would if incinerated, become dead and practically losing all its good reactive properties. Good quicklime needs to remain reactive. In my opinion and by evidence of thousands of years of low-temperature fired lime putty still in existence and working, I am going the low-temp fired route.

Part 1: The Big Question about repointing mortar for historic buildings

So what then is the cheapest and best alternative to use to repoint over historic lime and sand bedding mortar? That has been the question for many since the majority of those attending to repointing in the United States have been sort of stuck for years with knowledge of what we were ultimately looking for in properties for good mortar but somewhat limited in our range of available materials. In the past, every knowledgeable specifier new that too hard of a Portland cement based mix would impede vapor transfer through the mortar joint and cause the moisture to damagingly go through the face of the masonry unit or between a small crack that develops when the rigid mortar doesn't yield during building movement and the final result was a leaching out an unsightly deposit and worse. So the next logical thing to do, which has been done and is still being done for at least the last thirty years, was to make the mortar "high in lime content". The theory is to take the setting properties of a Portland cement and add more lime to the mix so as to aid in the mortar's ability to yield in movement and still allow vapor movement to go through the joint.

Part 2: The proposed problem in using any Portland cement for what we are trying to repair

A current existing argument in the industry about why not to use any Portland cement is that the presence of tricalcium aluminates, which is found in all Portland cement, when mixed with moisture, (which by the water can be egregiously trapped in a wall built with lime bedding-mortar when high Portland cement content mortars are used to repoint over the top of them), then forms damaging salts. A sulfate attack from this reaction is caused whereby an overall expansion occurs in the mortar and if allowed to go on will eventually disintegrate the mortar and even topple out sections of wall. So mortars containing any Portland cement may have this adverse reaction.  This reaction is controlled in a high lime content mortar containing Portland cement by a very tight pointing job and a building that moves very little and therefore shows little evidence of open voids from the  movement. In the past most everyone in historic masonry restoration was working with what they had and with what they knew even though most all restoration masons knew that the original lime/sand mortar joints may have been working very well for better than 100 years and couldn't argue that they would use the same if they could recreate all of what worked about it. Many of us in the industry were just not sure of the performance of high lime content mortars which contained Portland cement, but it seemed like a good fix until we find something better that would not also blow the job budget.

Part 3: The great solution that I found

Thank God I was introduced to St. Astier Natural Hydraulic Lime. When I found out all of its properties and its cost of approximately $26 per 55 lb. bag, not only did we get along, we got married. Like the commercial on television a few years back where the guy who enjoyed using a certain razor for shaving liked using it so much that he decided to just buy the company, it took very little convincing for me to jump right on board with the International St. Astier Lime Network.

St. Astier Natural Hydraulic Lime is High Calcium limestone burned at a low temperature using a low sulfur anthracite coal for fueling the kiln. The high calcium limestone they use naturally contains just enough reactive silica to cause it to become a hydraulic lime when it is burned and slaked and packaged dry, ready for the addition of sand and water to make great mortar. The term "Hydraulic lime" means that it sets up with the addition of water much like what all masons today are used to having happen when they make cementicious mortars. Lime putty made in the old fashioned way first described above needs six weeks of exposure to air in order to cure.  Masons today, for the most part, may not understand how to properly handle a good fat, wood fired high calcium lime putty until it is properly cured. Today's masons are mostly used to Portland cement mortars which are set in about two hours while this great solution that I found in Natural Hydraulic Lime sets in about two days. The word "Natural" hydraulic is important because lime can be made to become hydraulic by various methods, two of which are either adding Portland cement or slaking with sulfuric acid. All these things should be considered when choosing which lime to use.

I like The St. Astier Natural Hydraulic Lime company so much because they simply disclose everything they have and know about their material on their website so that anyone who wants to make an informed choice in specifying their product can do so by having this information readily available. So now I sell it in my exclusive territory from Pennsylvania to Maine and west for a total of 16 states. In just a short time I've been on the horn with international architects working on major national museums and world renowned universities for their historic restoration projects as well as their new build applications.

What should the owner of a historic home do if he needed work on this masonry?

Contact their local historic resources conservancy and ask for names of qualified architectural conservators who can first diagnose what intervention should occur in order to attempt to properly conserve his historic home and not introduce irreversibly damaging materials or methods of work. If the conservator or the mason does not know of St. Astier Natural Hydraulic Lime, he may want to become familiar with it by visiting and see if the material is appropriate for any of the fixes that the conservator suggests.

Do you have any examples of buildings that have deteriorated because of faulty repointing?

Examples are everywhere in the United States of faulty repointing. These examples are most prevalently seen and understood as a recognizable form of rapid deterioration, even by the untrained novice, where the faces of brick have hollowed out on a repointed building and the mortar remains protruding from the hollow, still intact as a "picture frame" around the brick. The mortar which "picture frames" the brick evidences high Portland cement content in the mortar by its very grey color and the deterioration that results is caused by the wetting and drying cycles occurring though the brick unit and not the mortar joint.

When/how did you learn of lime putty?

The entire history and theory of what was the everyday way to make mortar, with good, fat lime putty in all the ages of masonry past, was discussed at the trade school I attended. However, after we learned why every town in Pennsylvania seemed to have a road named something like "Limekiln Pike" where our forefathers cleverly named the road to lead masons to the lime, we went on to use only hydrated lime and sand to build shop projects. We used lime and sand mixtures exclusively for three years. We would talk to each other about the upcoming time when we would graduate and one day make mortar using Portland cement and hydrated lime instead of using just sand and hydrate.

The shop projects were temporary and were knocked down every couple of weeks so we didn't add Portland cement and create some homogeneous rock of masonry that we would have to tear down with much greater effort. Instead, we recycled the lime and sand and used it again and again on new shop assignments. However, may I note that if you finished a project the last week of school and no one knocked it down, and it stayed for the summer in the shop, the lime did get much harder and the project was much more difficult to knock down in the fall when we returned to school. You see, at the Williamson Trade School where I lived for three years to learn my trade, we had instructors who were there thirty years or better. So, my instructor was there from 1960 something and his instructor was there from, I think, 1930 something. Therefore, we did not feel far removed from the old ways of doing things in the trade even though the use of Portland cement was taught to us because it is now the staple binder of all modern construction mortar used for modern construction work.

Lime putty, not hydrated bagged lime, was reintroduced to me at various masonry restoration seminars as an option over 10 years ago, but more like an eccentric idea of a way to properly repoint buildings. Ten years ago it was just thought of as more limited than mainstream way of repointing buildings and just "some purists" were going back to using lime putty and the word on the streets was with failures and other varying results in final outcome. What I know now is a world away from those darker days.  Now I know how and why it works, where to get it and how to use it and when Natural Hydraulic Lime can also be used as a substitute for wood fired high calcium lime putty. I am changing the way I do everything and it turns out I am  going back to what we did for the first three years of trade school…using mixes with just lime and sand in them.  The only difference is that Natural Hydraulic Lime/sand mixtures reach durability strengths much like that of the original lime mortars used to build historic buildings where hydrated lime/sand mixtures does not.

Is there any resistance in the construction market to the older mortar?

I think I answered that question in my long dissertation first composed. Wood fired high calcium lime putty is expensive and therefore resistance to its use in historic restoration has been the norm. The other inhibiting factor is that people are afraid of what they don't understand. This is why I am posting this information on my website. Natural Hydraulic lime is relatively cheap, available, and has the right properties for many applications such as repointing over historic lime/sand bedding mortar. I think no-nonsense masons everywhere will come to find these things out and will then have less and less resistance to going back to using lime.

Could you describe your background, when you started, your current position, what town is your business, what town do you live, how long have you been in business, etc ?

For three years I lived at America's oldest private free trade school, The Williamson Free School of Mechanical Trades in Media, PA. I was enrolled to learn only the masonry trade. When I graduated I worked for two contractors over a two year period as their mason. I felt I could do a better job in running my own business so I started it in 1984.

Only six months into business I was asked to repoint a Pennsylvania Stone Farmhouse. My helper and I loved doing the work so I began taking courses and seminars on the subject of masonry restoration, collecting books about the subject, and soon found that this was the full direction our business took. I still have the same helper who started with me about 18 years ago. He is now an unbelievably good stonemason and restoration professional. I also have other men with me over 15 years. We are like brothers. I am not one to change much. I married the girl I met and dated from 11th grade until she graduated from college. Audrey, my wife, does my company's books along with two other secretaries. Audrey would never ever ask me about lime anymore - she knows better. This is the sort of long winded response I tend to give so I thank you for allowing me this wonderful opportunity to type these responses and have a sounding board. Seriously, she and the whole company know that I love what I do and I feel very well supported in this my life's work. I am truly grateful for great friends and family. I was born in Philadelphia, raised in Plymouth Meeting, and then shortly in Lansdale, PA. I moved to Quakertown when I got married and have lived and worked here ever since.

Could you name any big projects you've been involved in?

Every project whose owner wants correct historic restoration work is "big" in my book.  We take pride, like anyone would, on bidding jobs over one million dollars or for famous people. However, we take greater pride that we are not too proud to do a small repair if we are able to it. I think it is an honorable thing to perform the trade correctly at any level whether it be for a little old lady living in a pristine brick Victorian home here in town, or for a television personality dropping a couple of million into a weekend getaway pad built in the 1800's nearby. We have worked for both of these type characters.

Could you explain your part in helping to create specifications for state and national landmark laws? I think that's what I read on your web site.

Well, I have helped to simply write or re-write specifications. I explain the contents of my first dissertation, written above, to any and all captivated architects and conservators. I find that well educated and caring conservators seem to like helpful advise from a mason who makes a lot of empirical observations while attending to the work. This advice is then better supported because I also filter what I read about the subject and can then draw tangible conclusions on what I believe will and will not work or what may or may not be appropriate intervention. If I make a great suggestion that has any merit, often the specification gets rewritten. I try to practice being helpful in this manner at every opportunity I get in order to make the best outcome of the job. In one set of examples we won the award to work at William Penn's home, the founder of Pennsylvania, and also at the Pennsylvania's Governor's homestead of colonial days and I made certain masonry restoration suggestions.  The architect gave me a written referral letter about this.  I quote:

"I recommend Mr. deGruchy for any masonry work you'd envision. I have confidence in his skills and I trust his judgment. During our two projects, he was not shy about offering suggestions to make the jobs better, and I listened carefully and took his advice. In the end, I appreciated his willingness to share his expertise, and I believe it made the jobs better than if he'd simply "stuck to the specification.

--John R. Bowie, A.I.A., Historical Architect

This is just one example. Your question, Diana, does however encourage me to post on my website other reference letters which we have collected from those who have stated how much they enjoyed working with us.  I should do this because potential new customers like to see all our review letters. They usually ask me how we keep those who become our customers so happy that we get a lot of shining reviews. I always tell them that I simply attempt to completely fulfill my duty and do exactly what I say I am going to do. That may be what is always expected from a contractor, but for some reason many contractors are known to do the opposite. I believe that by not quickly entering into every agreement but by first making sure a good environment is set in which to do this labor of love, better than expected restoration work results.

Over and over again I read what is written in a specification and I will ask the specification writer why we are not doing it this way or that. This costs me jobs sometimes. I think it is for the best, at least for me. I always worry if a specification writer can not be open minded and work with me when I point out what I think is a questionable intervention. I don't want to usurp anyone's authority. I just want to start a healthy dialogue for the good of the work we will soon endeavor to do. An atmosphere of cooperation among all involved parties in a restoration project makes a better job in my opinion. I often suggest that if it is ever possible, an owner should choose to work in an open-ended-agreement with a good masonry restoration company and a qualified conservator rather than poise a low bid winning contractor against an unqualified specification to accomplish a very expensive mess.

On a national level, I am very proud to say that I've even been elected by my peers along with 59 other people to take part in an intense dialogue planned in New England in the early summer to discuss how to positively impact the next 25 years of our nation's historic built environment. This formal session is being modeled after a similar forum which was guided and funded by the same private foundation in another country with great success upon conservation of their historical heritage. Since I am not sure that I have the liberty to disclose the name of this private group I think I should just say that in any event I am honored to be considered among what appears to be a very select group of architects, engineers, academicians and public policy influencers. I intend to do my best to serve God and country with the grace that our dear God allows.

Andrew deGruchy, President

deGruchy Masonry Restoration, Inc
Quakertown, Pennsylvania

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Lime putty for mortar has been in known use for 6000 years. Modern portland cement lime and sand mortars have dominated for less than 100 years with many known failures. Here are what some modern scientific investigations have found about what worked so well about lime mortars and why so many modern mortars may not be appropriate for historic restoration. This information is offered so that you can make an informed choice on which binder to use for your projects.

This cross section cut away of a traditional lime putty mortar demonstrates via the blue dyed epoxy resin which fills the open pore structure that historic mortar based solely on lime and sand has a tremendously high and desirable liquid and vapor permeability. Note that the pore structure is still open but finer and more dense than the Natural hydraulic lime #3.5. This mortar is suitable for copings, parging and pointing in extremely wet conditions including sea driven rain with high salt content.
Note the high porosity in this mortar fabric. The wall can breathe by allowing moisture to enter and deliver the carbon dioxide needed for carbonation during curing and to usefully encourage the crystalline bridging phenomenon,(also known as the autogenous or self-healing properties of lime mortar), moving about the free lime in the mix to close larger fissures. Excess moisture then quickly evaporates back into the atmosphere. Note the dense fabric and the greatly reduced porosity with only the presence of shrinkage cracks. The shrinkage cracks are a portal for moisture to get into the absorptive bedding mortar (usually of lime and sand.) Normally, the sun will draw moisture back out of a lime joint. However, because of this portland cement based mortar, the inevitably supersaturated wall of trapped moisture can only have rain driven much further into the building and then to rooms when heat inside draws moisture, or out through the historic brick or stone accelerating its deterioration.
Petrographic thin section images courtesy of William Revie of The Construction Materials Consulting Group; Striling, Scotland.
© 2003 Pennsylvania Lime Works


OPC Ordinary Portland Cement Hydrated Lime Lime Putties St. Astier Natural Hydraulic Lime
Purity (Blended Material)

(Vapor Exchange Quality)

Resistance To Salt
Suitable Compressive Strength
Self Healing
Proficiency of Application
Resistance To Sulfate
Absence of Detrimental Chemicals
Slow Final Setting
Quick Initial Setting
Low Density

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Why Use St. Astier Natural Hydraulic Lime For Historic Restoration, Conservation, and New Build Projects ?
As late as 1940 many brick and stone buildings were constructed with lime and sand for mortar. Many times these limes were inadvertently hydraulic limes. The lime putty used may have had a hydraulic set because of impurities in the limestone when a limestone contained various degrees of reactive silica and was burned along with the pure calcium carbonate stone. Today it is unfortunate that many of these pre-1940 buildings have been repaired using Portland cement based mortars and stucco. There are some consequences with this remedy:
Because all buildings move, cracks develop in rigid Portland cement mortars and stucco. When a Portland cement mortar is stronger than the brick or stone laid up in the mortar, cracks that develop will transfer to the face of the exterior masonry allowing water penetration. Water can then be driven deeper into the masonry as it migrates to inside spaces.

Because Portland cement has a dense pore structure and a needle-like crystal structure that has the same expansion and contraction coefficient as steel, the unyielding joints and stucco will eventually crack in various places. This is especially true with free standing church bell towers and the like. Water that does not migrate to the inside of the building may evaporate out of the more porous soft brick or sandstone and only accelerate its decay. The mortar on the other hand will remain proud as the masonry units will decay back and finally hollow out from their original face plane.

*A contribution of the National Institute of Standards and Technology.

Tricalcium aluminates and Tricalcium silicates which form during the burning process of Portland cement have a detrimental chemical reaction when they come in contact with water that gets trapped in the bedding mortar and salts which are found in old buildings. This reaction results in what is called “The sulphation of cement” and is known to bulge once sound masonry walls as expansion occurs with this reaction sometimes causing even massive stone walls to topple over.Lime, however, has an open pore structure and a hexagonal crystal structure which allows the plates to shift between one another and yields flexibility and high vapor and liquid permeability. Some advantages of lime mortars are:
  • Walls breath better and moisture can escape
  • Mortar and stucco does not set too hard
  • Thermal movement can be accommodated without damage
  • Expansion joints can be avoided
  • Insulation is improved and cold bridging reduced
  • There is a reduced risk of condensation
  • There is little risk of salt staining because salts get flushed from wall surfaces
  • Masonry life is increased
  • CO2 emissions in the manufacture of lime are 20% less than cement and during carbonation of the lime, the mortar and stucco reabsorb considerable quantities of CO2
  • Natural Hydraulic lime gives an excellent reproduction of sand color
All St. Astier NHL mortars can be reworked (8-24 hours), reducing waste of material and increasing work rate due to its hydraulic set. St. Astier NHL contains no cement, gypsum, pozzolans, tetra calcium Aluminoferites, (high in Portland cement and contribute to expansion when reacting with gypsum.) St. Astier NHL does not have high aluminates, Sulphates, Alkalis making it suitable for marine environments.

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Here's How St. Astier Natural Hydraulic Lime Plays An Important Role In Construction As A Green Build Material

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St. Astier Natural Hydraulic Lime, or NHL, is a 100% natural product and does not contain any additives. It is one of the "greenest" materials used in construction. This is due to its purity, its calcium carbonate composition, its longevity and potential for allowing the materials to be reused or recycled, and the result of a low energy production process.

  • The amount of energy used at the production stage is one half of what is needed to produce cement. Consequently, the release of CO2 into the atmosphere is reduced considerably. Furthermore, NHL reabsorbs most of the CO2 during the curing process, while cement reabsorbs none.
  • NHL has received the LABELVERT EXCELL, or "Green Label", in France. This label guarantees the total absence of contaminants and any risk of pollution. It also authorizes the use of this product in chemically sensitive areas such as living spaces, wine cellars, etc.
  • The absence of detrimental chemicals like tri-calcium aluminate, potassium and sodium oxides (which are ever-present in cement), protect NHL mortars from chemical reactions such as sulfate or alkali attacks.
  • Very rapid evaporation of moisture from NHL mortars ensures that the drying cycle is faster than cement mortars and subsequently the healing requirements are lower.
  • Material used in construction with NHL may be reused or recycled. In addition, the NHL mortar itself may be recycled in a number of ways, such as an aggregate for new lime mortars, fertilizer (NHL is calcium carbonate), or it can be used for water purification to adjust pH levels.
  • Breathability, elasticity, plasticity, gradual development of strength, low shrinkage, longevity, CO2 absorption, self-healing through the use of free (or available) lime in crystalline bridging to close minor fissures, are all highly desirable. These traits, with sustainability and "greenness", are only some of the qualities of St. Astier Natural Hydraulic Lime.
  • The change-of-use of older buildings through adaptation or preservation and restoration maximizes the need for the environmental recovery of materials. It is essential to ensure the long term survival of these structures with compatible materials. Some buildings have been in use for centuries; there is no logical reason that this cannot continue. Preservation, adaptation and restoration can have significant environmental advantages over new construction. Aside from the environmental impact, there is the aesthetic value in preservation. Natural Hydraulic Limes have a significant part to play in the process.
  • Material longevity is unsurpassed when applied and maintained correctly and its life will span over several generations. The manufacturer's warranty subsequently extends for 50 years.

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St. Astier Natural Hydraulic Lime For Exterior Stucco Over Brick, Stone, And Straw Bale Construction
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The bonding characteristics of pure NHL mortars, combined with good background preparation, correct suction control, appropriate binder : aggregate ratio and good workmanship will ensure the durability of an exterior stucco plaster.

Bonding to the background and between subsequent coats is essential. This is provided by ensuring that the background offers a good key, by controlling the background suction in brick and stone and by casting on/harling at least the first coat on smooth or poorly keyed surfaces.

First coat (bonding coat): This is normally rich in binder. It's functions are mainly to ensure a strong adhesion to the background, provide the anchor for the subsequent coats, and compliment the water resistance of the intermediate coats. SUCTION CONTROL: SOME BRICKS ABSORB 1.5 LITERS OF WATER OR MORE  

Intermediate coats have insulation properties and protect against water penetration.
Their thickness vary in relation to climate and exposure.

The finishing coat is primarily decorative but can also serve as the first protective barrier, depending on the type of finish chosen.

NHL mortars will combine the ability to resist water penetration while allowing the structure to breathe freely. Values above 0.5 grams of pair per m2 per hour are acceptable. NHL mortars have between 0.55 to 0.75 (the value of concrete is about 0.15).

Allowing structures to breathe reduces or eliminates condensation and rot and enhances the living environment.


The elasticity of pure NHL mortars and the near zero expansion in NHL binders are such that joint free construction is possible.

Expansion in all pure NHL binders is below 1mm (measured as per EU Norm EN 459.2/

All St. Astier mortars can be reworked (8-24 hours), reducing wastage and increasing work rate. This is due to the absence of cement, gypsum, pozzolans, or high aluminates.