More About Lime Mortar and Brookline

Brookline provides church restoration services with general contracting of all trades. Brookline emphasizes the use of green building products in all phases and types of construction.

Lime mortar is a very green building product. Since lime mortar is fired at much lower temperatures than ordinary Portland cement, it uses much less fossil-fuel energy for manufacture than its mortar counterparts.

Green building starts with products that positively affect the atmosphere. Lime mortar and limewash absorb CO2 out of the air over the course of their entire life, which may be over 100 years!

Carbon dioxide is a major concern for many scientists and environmentalists, and many point to elevated CO2 levels as the reason for climate change. Products that absorb CO2 are truly green products of a rare quality. Natural lime putty mortar is such a product, which Brookline uses exclusively for historic masonry restoration.

Brookline combines historic preservation contracting expertise with a commitment to the environment. This unique company has been in business for almost 30 years, providing clients with excellent service, competent direction, and fair prices! Even the General Services Administration (GSA) of the U.S. Government has utilized Brookline's expertise on some of the oldest and most historically significant buildings in the nation's capital. From consulting to Building Evaluation Reports to historic preservation contracting, Brookline offers a wide array of services for church restoration.

Churches are some of our most culturally valuable structures, which must be preserved for future generations. Brookline's commitment to preserving historic buildings and to the environment makes it the company to turn to for real historic church restoration and general contracting for all trades.

Portland Cement Mortar Wrecks Historic Buildings

Portland Cement Mortar Wrecks Historic Buildings

The most common mistake in historic masonry preservation is using the wrong mortar. By wrong, we mean a mortar that is not compatible with the masonry units, or one that contains Portland cement in any quantity.

Portland cement is sometimes compatible with certain hard stones in terms of hardness, but it is never the right choice because it is not breathable and does not last long enough to qualify for historic preservation. It is not an historic material, and it is inferior to lime mortars in most respects.

The photo here illustrates an extreme example of what happens when soft, historic brick is pointed with Portland cement mortar.

The mortar shown is Portland cement. It is so much harder than the brick. But the other problem here is that the porous bricks take on moisture from the atmosphere, precipitation, and the building's interior, and the Portland cement will not let it pass. That is true even if it is a Type O (low Portland content) mortar. There is no breathability or flexibility, so it chisels away at the brick, and causes moisture to freeze in the wall instead of escaping.

Why is Portland cement used?

Portland first came into common use in the early 1900's in this country. It was first made in the U.S in 1907, and by the 1940's was pretty universal. Masons liked it because it sets relatively fast, so buildings could go up faster. When using lime mortar, the set times are longer because it is a different chemical process altogether. If the mortar sets fast, you can lay more bricks at a time. Everybody likes fast!!

The problems inherent in Portland make it far inferior to lime mortar in the long run. Sure, you may get the building up a few weeks sooner. But it is going to be coming apart a few decades sooner too!

It is counterintuitive to use mortar that is softer rather than mortar that is harder. After all, wouldn't you think that harder is better?

Someone unfamiliar with the different kinds of mortar thinks so. But it is just the opposite. Mortar doesn't have to be all that hard unless it's a 20-story building. For most historic buildings, the compressive strength doesn't have to be 1/10th the strength of Portland mortar.

Remember, the most important characteristics of mortar are 1) breathability and 2) flexibility. Portland is fine for building skyscrapers and Hoover Dams. But when restoring an historic structure, going back to a compatible mortar means using lime mortar.

Brookline uses Lancaster LimeWorks supplies natural lime putty, mortars, and limewash to the historic preservation industry. Contact us at 717-207-7014 today to order.

Lancaster Lime Works

Brookline Builders is now using Lancaster Lime Works lime putty mortar and stucco's. Here is a description of the company.

Located in Lancaster, Pa., Lancaster Lime Works is a manufacturer of lime putty and lime putty mortars for repointing and historic masonry preservation of all types. Lime putty is the binder for all of our products. Lime putty can be made into mortar, stucco, plaster, and limewash (whitewash), and is also a key ingredient in historic paints.

Lancaster Lime Works is also a reliable source of information and training related to the installation of lime putty, lime mortar, limewash, and all questions relating to historic masonry restoration and historic preservation in general. Lime putty mortar is very different from hydraulic lime mortar and Portland cement mortar, mainly because it is made from pure calcium carbonate with no clays, silica, or other impurities that give them the ability to "set" under water.

Lime putty mortar is much more flexible and long lasting than hydraulic lime mortar or Portland cement. It is the ideal choice for repointing brick and stone because it is softer than the masonry units that it is bedding. Therefore it can flex with building movement, and can even heal itself (called "autogenous healing"). Because of the flexibility and breathability, Lancaster Lime Works highly recommends its products for stucco applications.

Lime putty stucco can be direct applied to brick or masonry substrates, as well as wood lath and straw bales. It can also be used successfully in interior applications, especially where moisture may be present in small amounts. It is breathable, so it does not trap moisture in walls and other structures, eliminating mold and mildew problems that are often associated with modern repointing and modern plasters/drywall.

Lancaster Lime Works takes pride in producing and selling truly historic products for masonry restoration nationwide, and providing training in the proper installation methods for all of our products. Installation of lime putty products is not difficult; rather it is a very workable and forgiving material. Lime putty installation is very different in every way from conventional masonry materials, and knowing how to install it is critical to a successful installation.

Lancaster Lime Works is the source for retail and wholesale lime putty and lime putty mortar, stucco, plaster, limewash, and historic paints. Lancaster Lime Works can assist specifiers with specifications for historic building and restoration projects.

DESCRIPTION OF LITHOMEX REPAIR MORTAR

DESCRIPTION OF LITHOMEX REPAIR MORTAR

St Astier Natural Hydraulic Limes (NHL) Specially formulated mortar, based on Natural Hydraulic Lime and aggregates for the repair or simulation of masonry, brick or stone. Lithomex is a neutral white or pre coloured mortar to which mixing water is added.

Shaping and forming of details can be carried out for up to 1 week after placing by scraping to profile or level with metal tools, such as the edge of a trowel or steel float however most shaping and finishing work can be done within 24 hours. Sculpting, using appropriate tools, requires waiting up to a week or more depending on the weather conditions. Its unique qualities allow it to be tooled, shaped and sculpted even after the final set has taken place. This affords sufficient time to achieve the very highest standard of work with the best quality reproduction.

Where ashlar masonry or very finely jointed masonry has had considerable damage to the arises, flush finishing in Lithomex with a false struck joint is the ideal solution. If building details are damaged and require repair prior to the facade being lime washed or painted, plain Lithomex should be used as it will readily accept lime washes and paints. On rendered areas Lithomex can be used to form decorative stone or brick features such as mouldings and cornices.

GENERAL PROJECT CONDITIONS FOR USING LIME MORTAR

GENERAL PROJECT CONDITIONS FOR USING LIME MORTAR

1. Bedding and lime pointing mortar should be placed only if air and masonry temperatures are between 40°F (4°C) and 80°F (27°C), and the air is relatively calm. Conditions must remain so for at least 48 hours after completion of work. If conditions are not within these parameters, Contractor shall take all necessary measures to ensure that the manufacturer recommended protection and curing requirements are met, including as necessary, dampening of burlap, polyethylene sheeting, wind barriers, and other protection as needed.

2. The wall must be thoroughly wetted down at least 24 hours before work is begun. The wall must again be wetted down at the begining of the day then be monitored thru-out the day. If the wall drys out it will suck the moisture from the lime and the lime mortar will not reach it's compressive strenght.

3. Contractor must be aware that working conditions change thru the day. In the morning hours the temps will be cooler and the surface will not have direct sun. In the afternoon the mason must provide proper shade from direct sunlight or the lime will dry out to quickly. All masons on the project must constantly monitor the prewetting conditions and apply more water as needed to keep the wall at a proper moisture content.

4. Contractor shall not start work until joint faces and solid bedding have been prepared as approved.

5. Contractor shall not allow direct weather related water against mortar until it has reached its full cure.

These general guidelines for working with lime mortar are not complete and should only be used as a starting point. Using Lime Mortar requires extensive training. Contact Brookline for more information on how to use Lime Mortar and to purchase it.

DESCRIPTION OF LIME MORTAR

DESCRIPTION OF LIME MORTAR

Lime mortars have been used since time immemorial. With lime mortars all our buildings, prior to the advent of modern cement after 1915, have been built. The survival of most of these buildings for hundred and even thousands of years is a testimony to the durability of lime mortars.

Lime is produced by burning limestone (CaCO3)at temperatures below 1250oC traditionally in vertical kilns loaded from above and for a period of up to 48 hours. The material extracted from the furnaces is Quick Lime (CaO), typically in lumps. These, when in contact with water, exothermically disintegrate into smaller pieces varying from friable chunks to very fine particles. The process of water addition is called Slaking, hence a slaked lime is quick lime that has been hydrated or Hydrated Lime. If necessary the slaked lime is ground, once cooled down, into fine powder and bagged.

During the burning the limestone (CaCO3) loses CO2, hence the quick lime has the symbol of CaO. When exposed to air, some CO2 is reabsorbed, reconstituting CaCO3 or limestone. This process is called carbonation and its result is the hardening of the lime. In a mortar the lime has bound together the aggregates and by hardening produced the hardening of the mortar, normally expressed as Compressive Strength. Carbonation is a slow process and in damp or wet environments, is impeded by the moisture patina which forms over lime mortar surfaces obstructing the contact with air.(Lime mortars which are not hardened are very susceptible to adverse weather conditions and, in cold climates, can be easily damaged by frost.

If the limestone being burned contains hydraulic components (hydraulicity is the property of hardening in contact with water) such as silica (SiO2), alumina (Al2O3) and ferrites (Fe2O3) these will in total or part combine with the CaO forming Calcium Silicates, Calcium Aluminates and Calcium Ferrites. These combined elements harden in contact with water, producing Hydraulic Limes.(Mortar made with hydraulic limes will harden quicker that air lime mortars and will have a better performance in cold climates.

Today we are charged with the responsibility of ensuring the survival of our historical and vernacular built heritage through careful and considered conservation, restoration and renovation. All too often buildings are repaired with inappropriate materials and poor skills. Many are the subject of interventions that in time lead to their total loss. Others are simply changed out of all recognition. In most cases, the mortar used for repairs, restoration or conservation contains cement. In these buildings, the use of cement mortars promote condensation build up, salt reactions and, generally, drastically affects the long term survival of the building. Historic Masonry Repair for Brick and Stone Homes

Preparation for Repointing Brick or Stone

How to Remove Mortar Before Repointing

The biggest challenge in restoring masonry walls and buildings is replacing Portland-cement-based mortars with a natural lime mortar. The difference between the two is easy to determine. Using a pointing chisel to remove lime mortar is quite easy; the mortar is soft and breaks easily in front ofthe chisel. Portland-based mortars are quite hard, and hand-chiseling takes many blows from the hammer to remove just a couple inches of joint.

This hard mortar is very damaging for brick and soft stone. One reason they are so damaging is that Portland-based mortars (Type N, Type S, and most mortars available today) are not water permeable, so they do not allow moisture to escape from the wall. Also, Portland-based mortar is not flexible, but brittle, so the masonry units are stressed by freezing temperatures and imperceptible building movements. This can take the faces of brick right off of buildings that should be preserved and protected. Natural lime mortar will wick moisture away, and flex with the small movements of temperature changes and settling that occurs in every building over time.

To remove Portland-based mortars efficiently, a grinder should be used to cut a groove in the center of the joint. Usually a thin blade works better than a thick one, and a 4" blade will cut through the Portland-based pointing back to the original lime-based mortar. Cutting the center of the mortar joints prevents slipups from damaging the original brick or stone. Special care should be taken on head (vertical) joints to cut only as deep as the grinder can without cutting into the masonry units. This can take strength and focused attention because the grinder is harder to control when removing very hard material. Center-cutting the joints relieves the pressure that the hard mortar puts on the faces of brick and stone.

The second step is to hand chisel the joints out. Usually the best method is to place a flat chisel right where the mortar meets the edge of the brick or stone, aiming toward the center groove that was cut with the grinder. A pointing chisel can also be used to go across. Pick a 2"or 3" section of joint and aim the pointing chisel toward the area that has already been removed. The chisels will break the bond between the Portland-based mortar and the brick or stone.

Usually the repointed joints are less than an inch deep, so removal is safe as long as care is taken with the faces of the masonry units. Remove mortar at least 2x the height of the joint. A 3/8"-wide joint should be chiseled back to at least 3/4". This will ensure an adequate bond between the new mortar and the brick or stone.

Once the mortar is removed, the joints should be vacuumed, or blown out with compressed air. A low pressure jet of water, such as from a nozzle on a garden hose, can also be used. If the joints are vacuumed or blown out, it is a good idea to dampen the wall before applying the new mortar.

Never use a pressure washer on soft brick or stone. High-pressure water can damage walls of even hard stone (like granite), so the nozzle should be kept well back from the face of the stone. Pressure washers often remove the beauty of the weathered faces of stone, including the green moss that can make a building look old.

Hydraulic Lime Mortar On a Chimney Cap?

As a company, we are committed to the challenge of using sustainable building methods in our historic restoration projects. Sometimes we are asked specific technical questions as to how these two objectives are reconcilable--how can we use historic methods over modern techniques to stand the test of time? Recently, we received just such a question: "I am committed to using the sustainable and historically accurate natural hydraulic lime mortar on my chimney cap, but how will the natural lime mortar hold up in the long run?"

This is a valid question. After all, Portland is harder than natural lime mortar, right? So although it is historically accurate, how is it sustainable to use a softer material on a chimney, one of the hardest to reach places and one of the most vulnerable spots on your historic house? Shouldn't your chimney, of all places have a durable and water proof cap? Beautiful homes, that have been meticulously maintained, have often been found to have small plants growing out of the chimney.

First let's consider a few of the attacks a chimney has to endure. The most obvious is the extreme exposure to all forms of moisture: rain, snow, dew and frost. Constantly varying temperatures throughout the year, from cold winter nights to scorching hot summer days add an additional assault on the chimney--the constant expansion and contraction takes its toll. In the dead of winter, when the furnace kicks on and 400 plus degree air suddenly hits a 15 degree chimney flue, then what happens? The resulting pressure has an effect much like putting an untempered glass into a hot oven: it cracks. This expanding and contracting phenomenon has another destructive effect; the clay liner which your chimney is built with will expand upward as it heats up then contract back down as it cools. This effect may further compromise your chimney's structural integrity. As if this was not enough, a surprising attack comes from another part of nature. A chimney is a natural resting place for birds. We have seen the corrosive effect that bird droppings have on the integrity of a chimney cap. While we won't attempt to address all of these issues here, we will address the basic way that we apply a chimney cap.

Needless to say, the chimney has a very difficult and challenging life and it would be advisable for the responsible homeowner to inspect a chimney for integritymuch as he would inspect his gutters for leaks. Just as a leaky gutter will ultimately wreak havoc on any masonry construction, a leaky chimney will do the same. Add the chimney cap to the schedule of five year maintenance checks. Eventually, you may have to repair it, or even replace it completely. As I like to say, a chimney cap replaced in time can save nine.

So, now let's go back to the historical use of hydraulic lime mortar on the chimney cap instead of Portland. Portland is harder and water proof right? Doesn't that mean it will last longer, and need fewer repairs? It's a good theory. But there are more destructive forces at work on a chimney cap than just moisture.

Recall our description of one of the most destructive attacks: thermal expansion and contraction from the flue gasses as they heat a very cold chimney. Portland may be harder, but hardness doesn't handle that kind of expansion very well, it cracks easily and once it cracks it doesn't heal. Earlier, we raised a concern that natural lime mortar is softer, right? But now we see that the softness is a positive thing because it will permit more movement than Portland. If it does crack, it heals itself! This is how it works chemically: the content of natural free lime actually attracts to itself and thus it self-heals, sealing the crack.

The tried and true method we use to apply a chimney cap is as follows:

We apply three coats of mortar. The first two coats consist of two parts course concrete sand, one part 3.5 natural hydraulic lime mortar, and one handful of natural hair or fiberglass. The third and final coat we apply is proportioned as follows: two and one half parts sand, one part 3.5 natural lime mortar, this final coat has a bit more sand; no fiberglass or hair. This method will allow the first two coats to act as a stronger mixture--the fiberglass acts as a rebar of sorts-and the final layer seals the fibrous ends so they won't act as a wick for water absorption; we don't want a conduit for moisture. For a few weeks after the new chimney cap has been applied, it should be covered from moisture-depending on the temperatures-and should be kept damp in hot temperatures.

While the exact method of applying a new chimney cap may vary extensively, we have found that our method works quite well and lasts for many years. It is our commitment to balance the use of natural and sustainable products, while enabling the use of historically accurate products and procedures.

Chimney Repointing

Brookline Builders will repoint and rebuild your old chimney with Natural Lime Mortar. The reason most chimneys fail is because of water penetration. If a cap of either flagstone or metal is maintained and installed on your chimney, the water will not penetrate and your chimney will outlast the roof. If water is not kept out of your chimney it will deteriorate extremely fast, especially in the winter during freeze thaw cycles. If your chimney needs to be rebuilt don't ever use portland based mortar, especially on a chimney.

Portland will not withstand the expansion and contraction of an exposed chimney, it will crack quickly then fall apart in just a few years. This is because portland based cements are water proof, so once the water penetrates into the chimney, and it will, the portland does not allow the moisture to escape. This moisture that is trapped in the exposed chimney will expand when it freezes and thaws. Over a few years the effect of this cycle the chimney will blow apart.

The key to repointing an historic chimney is to not use any portland cement. Rather use natural lime mortar. Natural lime mortar will allow trapped moisture to quickly escape and will self heal any cracks. The pyramids in Egypt were built using natural lime mortar. Portland cement wasn't widely used in the US until the early 1900's.

Hydraulic Lime Mortar Contractor -- PA

Mortar and Longevity: Will Our Buildings Stand the Test of Time?

Did you ever look closely at the exterior of brick or stone home, and see hairline cracks running up the wall? Or sometimes the mortar joints have lots of cracks running across them, so that the mortar looks like it could fall out in 3-inch sections. Even an old (or not so old) concrete block building, like a garage, can have joints cracking out all over the place.

Natural Hydraulic Lime Mortar

Whether your a homeowner, or someone in the building trades, you may have noticed mortar joint failure, and maybe you had a thought like, "What is going on here? I thought masonry was the best exterior-supposed to last forever!!!"

Isn't a stone home supposed to last forever?

What about the castles in Scotland and the palaces in Prussia??

We are stonemason's, and these are questions we have started to ask also. For us, our livelihood depends on the answers because we can already see cracked mortar joints in work we did 5 years ago! Could the mortar that we were trained to mix and use be flawed?

Why do patios and sidewalks crack so quickly-often in less than 10 years? Why does almost every stone, brick, or block building show cracks in just a few years after it's built? That's not the longevity we expect from using such historic and time-tested materials!

Materials scientists have been asking these same questions. After studying those castles in Scotland and masonry buildings all over the pre-modern world, the answers are starting to come out. Turns out the mortar we use today is not at all historic. Time has tested it, and it is failing the test.

A little construction history might help at this point. For at least 7,500 years, man had been using (roughly) the same process to make mortar: burn high-calcium limestone by layering wood and stones inside of a really fat chimney (kiln) and then lighting it on fire. The resulting burnt stones are then crushed and mixed with sand and water to make mortar. The burnt lime reacts with the water, causing it to get sticky and then harden, lasting for centuries or longer in between the stones in a wall.

This lime is called hydraulic lime because it hardens without the presence of air. Getting hard is a chemical reaction that is different from just drying out. It will get hard under water.

Now don't confuse hydraulic lime with hydrated lime. Hydrated lime is a different process, a different material altogether. Hydrated lime can't be used as the binder in mortar because it never gets hard. Hydraulic lime does.

Now, jump forward in the history of mortar to the late 1800's when various inventors began experimenting with new processes and materials for making cement. Portland cement, the almost exclusive binder and hardener in today's mortar, concrete and stucco. It got its name from the Isle of Portland in the English Channel where limestone had been quarried for centuries and admired for its building qualities. By 1878, the British government had issued a standard for Portland cement, and in 1907, production began in the United States. It came to be the main ingredient in mortar and concrete throughout the country by the end of World War II.

Now, Portland cement has proven its superiority to hydraulic lime in many departments.

In the speed-of-getting-hard department: Portland's the champ.

In the waterproof department: no contest. Portland wins.

In the hardness department: Portland wins again.

Game over? Not yet.

As it turns out and according to research on the old hydraulic lime mortar, using Portland may be a strategic error. At least, as far as longevity is concerned.

It all boils down to the way we think about buildings and how they weather. Everyone knows that the point of a building is to keep out water, right? In recent decades research on building materials and techniques has gone farther and farther down the road of keeping out 100% of all moisture and all air. Now we are combating mold, air quality, and condensation problems.

But back to the Portland vs. hydraulic lime debate.

In the longevity department: no contest. Hydraulic lime wins. Hands down. Why?

Yes, Portland cement seals out water. Hydraulic lime allows water to penetrate. The problem is that most masonry units (like brick, stone, and block) absorb small amounts of moisture from the air and rain. Hydraulic lime acts like a wick to get that water back out-- FAST!! Portland won't let the water pass, trapping it in the wall where it does damage-cracking the joints and even the faces of the bricks or stones. That's why you see the faces of old brick buildings popping off. Repointing with Portland destroys the building-FAST!! Repointing an older building using portland cement starts the countdown to it's demise.

Yes, Portland cement is harder. But harder is also more brittle. Portland is fired at about 2,600 degrees Fahrenheit, as compared to hydraulic lime's 1,800 degrees. When you look at the two under a microscope, hydraulic lime particles are like plates that interlock; Portland's are like needles. Any movement in the building is going to make Portland crack all over the place, while the more flexible lime mortar can move with the building without cracking.

It gets better.

When you get down to the microscopic level, Portland cement has salts in it that actually degrade the mortar from the inside out. This stuff starts decomposing as soon as it gets hard!

You guessed it: hydraulic lime has a little secret of its own, and its not the kind that brings the wall down. Hydraulic lime has small amounts of free lime-lime that never reacted with the water in the beginning, after it was burned. This free lime actually dissolves in the water that is escaping out of the wall, and in the process it fills any cracks that may have formed. The experts call it "autogenous healing." Like a lobster growing back its claw, I guess.

No wonder they used it for 7,000 years, Plus.

No wonder the historic restoration movement is switching from Portland-and-lime mortars to historic, hydraulic-lime mortars.

Hydraulic lime is still a bit hard to find in this country. To my knowledge it's not produced in the U.S. yet. What we use is imported from France. Different grades can be used to make plaster, stucco, lime paint, mortar, and even concrete.

So next time you're wanting you're chimney repointed, a stone or brick historic building restored, find a historic restorations contractor who knows about hydraulic lime. As a mason, the choice is clear to me. What's the point of building new or restoring the old, if our work is not going to stand the test of time?

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