History of lime mortar

Lime mortar is composed of lime and an aggregate such as sand, mixed with water. The Ancient Egyptians were the first to use lime mortars. About 6,000 years ago, they used lime to plaster the pyramids at Giza. In addition, the Egyptians also incorporated various limes into their religious temples as well as their homes. Indian traditional structures built with lime mortar, which are more than 4,000 years old like Mohenjo-daro is still a heritage monument of Indus valley civilization in Pakistan. It is one of the oldest known types of mortar also used in ancient Rome and Greece when it largely replaced the clay and gypsum mortars common to ancient Egyptian construction.

With the introduction of Portland cement during the 19th century, the use of lime mortar in new constructions gradually declined. This was largely due to the ease of use of Portland cement, it’s quick setting and high compressive strength. However, the soft and porous properties of lime mortar provide certain advantages when working with softer building materials such as natural stone and terracotta. For this reason, while Portland cement continues to be commonly used in new constructions of brick and concrete construction, in the repair and restoration of brick and stone-built structures originally built using lime mortar, the use of Portland cement is not recommended.

Despite its enduring utility over many centuries, lime mortar’s effectiveness as a building material has not been well understood; time-honored practices were based on tradition, folklore and trade knowledge, vindicated by the vast number of old buildings that remain standing. Only during the last few decades has empirical testing provided a scientific understanding of its remarkable durability.

Masonry Cement vs Portland Cement

What’s the difference?

Masonry cement is a blend of portland cement, Type S lime, and probably other additives.  Masonry cement can be mixed with sand to get a portland cement mortar.  The normal mix is 1 part masonry cement to 2.5 parts mason’s sand.

Portland cement has to be mixed with Type S lime in order to be workable on the trowel.  The lime gives it a more sticky and “plastic” consistency that makes it easier to work with and spread.  Portland cement can be mixed with lime at a rate of 1:1, which as the binder can then be used with sand at the normal 1:2.5 or 1:3 that you might use with masonry cement.

If you mix portland cement with sand without adding lime, the mixture will be very sandy and impossible to spread.  It will still get hard, but it is very hard to use.

Please note that Type S lime is not the same lime that was used historically to make lime mortar.  Manufacturers fire the lime at too high a temperature for it to function as the binder by itself in mortar.

To obtain a lime that you can use to make lime mortar, visit Lancaster Lime Works.  Or call us at 717-347-5000 to discuss further.

Is Type O Mortar the Best Choice for Repointing?

Someone recently asked me a great question. It was related to a mid-1800’s brick home that needed some repointing and brick repairs.  The question was something like:

What kind of mortar would you use to repoint?  Would Type O mortar still allow the walls to breath?

First, this is an impressive question coming from someone without experience in either historic preservation or masonry.  It shows a high level of understanding of the needs of structural masonry walls and the importance of moisture-release in mortar!

You hear a lot about the “Types” of mortar in restoration circles.  Let’s dig into this a bit.

The Types of Mortar (K, O, N, S, and M) are based on ASTM standards for compressive strength. Compressive strength is how engineers measure the amount of load (weight, or pressure) a material can hold without compressing or distorting in any way. Compressive strength is measured in pounds per square inch (psi).

The strength of Type O mortar is specified as a minimum of 350 psi.  Type K is minimum 75 psi.

To put this in perspective, a structural masonry home (solid brick or stone walls that carry the whole weight of the house, contents, and roof) puts between 40 and 80 psi of pressure on the ground. The low end would be a large house with a slate roof and a typical footing, and the high end would be the same house with the maximum amount of people and belongings that the flooring would be able to handle.

So a typical large brick house built before 1920 needs a mortar of roughly 60-80 psi to more than handle the weight without the mortar failing, and Type O is 350+ psi !

You see, the compressive strength of the mortar is really not the issue. The real issue is how well does the mortar release water?

Unfortunately, nobody in the building trades is talking about or knows about the moisture-releasing capacities of materials.

The modern perspective is that moisture should be sealed out, which is contradictory to the very principles with which historic homes were built: the masonry can be in contact with the ground because the mortar releases the moisture without any damage to itself.

Not so with portland cement.

Here’s what you have to remember: mortar that is made with portland cement—in any amount—does not release moisture easily. Even a Type O mortar (way too hard for your bricks) is going to hold onto the moisture because it is made with cement.

The beauty of lime-sand mortar, such as what we use from Lancaster Lime Works, is that it has plenty of compressive strength for structural masonry, but releases moisture like your cotton underwear drying on a clothesline.

The problem in masonry restoration today is that most masons were trained to open a bag of mortar and mix with sand and water. But the bags are all just different percentages of cement and additives. Most know little about different kinds of lime.

You cannot even buy high-calcium lime-sand mortar at the masonry supply yards. Nor can you buy a lime there that will react with carbon dioxide and get hard enough to be a stand-alone binder in mortar.

There are only a couple companies nationwide making it, and it is a different installation process than cement mortar.

So the answer to the question is:

no, Type O mortar doesn’t offer any more breathability than any other cement-based mortar. Type K is the closest to correct because it is softer, which is better for your bricks, but still not breathable (vapor permeable). It just has a lower cement content.

We would use a non-hydraulic, high-calcium, lime-sand mortar (contains no cement), which is not classified with ASTM specs, but would fall in the range of Type K in compressive strength.

So if you are talking to a masonry company about repointing your pre-1900’s brick or stone house, insist they use Lancaster Lime Works mortar. LLW can provide them with training on how to install it.

Or, call Brick and Lime.

I have been working with building conservators for several years, learning about the characteristics of mortar and how to install it properly. I have overseen 4 projects for the federal government which involved lime mortars and cement mortars, including work on the Blair House and the Winder Building in Washington, DC.

Specifically, I was trained in lime mortar theory and installation by John Greenewalt Lee, and have worked with the conservators in the White House Service Center and the National Park Service in completing their projects with lime mortar and stucco.

They would all agree: your pre-1920’s house needs high-calcium lime mortar to perform as it was designed (release moisture without damaging the brick) and stand the test of time.

Moisture-releasing lime: it’s what makes homes historic

There is a fundamental difference between the way homes were built before 1920 and the way they have been built since.

(Of course, the year 1920 is an arbitrary. Home construction between 1910 and 1950 experienced an evolution towards present-day methods and materials, so there is some variation during that period.)

Before 1920, homes were largely constructed with structural masonry walls. This means that brick or stone was used to construct solid walls that went from the bottom of the basement up to the roof.

These solid brick or stone walls carry the entire weight of the house, the roof, and the contents of the floors.

The masonry (brick/stone/mortar) IS the structure of the house. It carries the entire load.

Homes today generally have concrete and cement masonry for the foundation, and then some kind of wood structure above. The walls are not made of structural masonry. Wooden walls can be covered on the outside with brick, stucco, wood siding, cement siding, or any number of materials, but the siding is a VENEER. That means it is a relatively thin covering for the wood structure.

On my 1950’s rancher, the brick is 4″ thick and covers the wood frame wall structure. The brick is supporting nothing except its own weight. It is a veneer.

We can discuss the pros and cons of structural masonry versus veneer masonry all day long. But the main point is this:

There is a very important difference in how these two types of construction function as it pertains to water and moisture.

Wood structures cannot be in contact with moisture, water, or any dampness. Obviously, they rot in these conditions.

Historic structural masonry has a secret weapon that allows it to tolerate some moisture with very little deterioration.

That secret weapon is lime mortar.

Lime mortar allows moisture to move through it without damage. Rising damp (ground moisture) wicks into the foundation walls below ground, and that moisture escapes from the wall inside the basement and above the ground, inside and outside the house.

Being able to release moisture into the air is a VERY IMPORTANT capability for masonry!

In fact, this moisture-releasing capability is why these homes are historic.  They have stood the test of time enough to be here with us still today, instead of being torn down and replaced.

Lime mortar makes this possible. It release moisture very quickly and easily.

Lime mortar = moisture release = longevity.

Contrast this with cement mortar. Portland cement holds onto moisture. Traps dampness in the walls.

That’s why it is so important for maintaining the STRUCTURAL INTEGRITY of a structural masonry house that lime mortar is used to do any restoration, repairs, or repointing. Especially in the basement and the bottom 6′ of the wall above ground.

Moisture-release-capacity MUST be maintained!

I have seen so many homes pushed to the edge of structural death by masons, contractors, and other home health “professionals” who were uneducated as to the characteristics of the mortar materials they used.

Portland cement mortar traps the moisture in the walls, which accelerates damage to the brick and the original lime mortar behind it, causing the whole structure to settle and move much more than it ever would have.

Not to mention plaster damage, frost damage, floor joist damage, window rot, and so on.

So as the owner of a structural masonry home, do not leave your brick repairs and pointing work to just anybody who has experience in masonry.

Those walls are the home’s structure. Those bricks are carrying the weight of you and all your possessions. That mortar is holding a roof over your head at night, decade after decade, as it has been doing for a century or more, and will continue to do for more centuries if it is maintained properly.

Beyond that, your structural masonry home is a valuable piece of the past. Each of these homes is like a brick in your community’s structure. Together, they are the legacy of previous generations of hard working Americans, and they should be preserved in their structures (if not their floor coverings, fixtures, and heating systems) for future generations of hard working Americans.

Structural Masonry

We do a lot of repairs to brick homes built before 1900.  These buildings are built very differently than modern homes.

Most significantly, the walls in one of these old homes are structural masonry, not veneer masonry.

Very important distinction.

Structural masonry is any masonry that is carrying the weight of the building or some part of the building more than its own weight.

Structural masonry walls carry the weight of the floors and the roof in addition to their own weight.

Structural masonry walls in a typical brick home built before 1900 start below the basement floor and go straight up to the roof.  Usually they’re 12″ thick in the basement, and then are 8″ thick up to the roof.  The floor joists are notched into this wall.  The roof rafters sit on top of the wall.

These walls are carrying the entire weight of the building, plus its occupants and their things, plus any snow that may be sitting on the roof.  This weight is transferred downward as pressure on the soil or rock where the house is built.

Veneer masonry is used in newer homes and is usually built on the outside of a house after everything else is built.  This brick “skin” carries no weight other than its own.

In these homes with veneer masonry siding, there is usually a structural masonry foundation (8-12″ thick concrete block), which forms the basement.  Floor joists are laid across the foundation, 2×4 walls form the outside structure, and this wooden structure carries the weight of the upper floors and the roof.

The brick is laid up as a veneer over the frame walls.  It’s a 2 layer system where the masonry is used as siding, but is not carrying the weight of the building.  Usually the veneer is 4″ thick in the case of brick, or 1.5″ thick in the case of fake stone or thin brick veneer.

So in the old homes, the brick is 8″ thick from the ground up to the roof, and carries all the weight.

In newer homes (post 1945, generally), the brick is 4″ thick and carries no weight.  It is just a very thin layer that would topple over if it weren’t tied to the building.

But so what?  Why is this important?

Because structural masonry homes are built in a very long-lasting way with mortar that is very different from today’s mortar, and this building system is not well understood by today’s contractors, masons, and homeowners.

These walls are constantly damp below the ground.  They are plenty strong enough to carry the load of the house.  They are flexible enough to handle the small building movements that occur in every building and still last for centuries.  And they are virtually maintenance free.

Modern mortar repairs, modern coatings, and modern interior changes are destroying these buildings because they are not compatible.  They trap moisture.

The resilience and longevity of the old structural masonry homes goes back to the mortar.

I’ll say it again:  It all goes back to the mortar.

The old mortar is strong, flexible, and allows moisture to escape very easily.

Modern mortar is super, super strong, very brittle, and holds on to moisture.

If your home is masonry and built before about 1920, please make sure your contractor is using compatible materials.

If not, there are easily avoidable structural problems and moisture problems down the road for you.

Brick and Lime: It’s How America Was Built

I’ve been working with brick and stone and mortar for over 20 years.  In fact, it was 21 years ago when I started building a cabin in southeastern Ohio on a piece of land I had inherited from my father.

That experience of building with hand tools and natural materials was what later motivated me to learn stone walling as a trade.  Stone captured my attention both as an art-form and a useful skill.

Mortar was always a big question mark for me, even 20 years ago.  Mortar is just the stuff between the stones (if you decide you don’t want dry laid walls), but it’s the stuff you can’t just go gather in the woods.  Unless you use mud or soil, mortar is a manufactured product that takes infrastructure and technology to produce.

And that bothered me.  It bothered me that I couldn’t make it myself (I am a diehard DIY-er), and it bothered me that the science behind it was obscure and hard to find, even with the internet.

Well, the science behind mortar is coming to light and becoming more widely talked about, and it’s not something that can be manufactured readily in one’s backyard.

You have to have a kiln.  The photo at the top shows one.

It is a fairly simple process, as manufacturing processes go.  After all, we’ve been making the stuff for thousands of years.

It requires a kiln, a recipe and some know-how, and a deposit of high-calcium limestone (with quarry equipment).

Like most other manufactured goods, the industrial revolution changed mortar.  The way it was understood and produced, the choices available in the marketplace–it all changed.

In today’s world, mortar is thought of as cement.  Mason’s generally know portland cement, Type S lime, and sand.  Small variations within those products.  Masonry cement is just portland and lime blended in a bag, and mixing with sand gives you mortar.

But in yesterday’s world, before the World Wars especially, mortar was understood as lime and sand.  Sure, cement was widely used by that time, but it took a long time for cement to reach the point of dominant market share as compared with lime for making mortar for residential construction.

Cement was required for concrete and for constructing tall buildings and industrial works, but for homes, lime and sand was the best mortar for masons to use to build brick and stone walls.

And it still is.

That’s why our name is Brick and Lime.  Not Brick and Cement.

Lime is 8% of Earth’s crust.

Lime has been used by itself as the binder in mortar for thousands and thousands of years.

Lime is the primary component of the best plasters in the world.

In other words, lime is the forgotten star of masonry construction and restoration.

Lime is what we admire about all the old homes and neighborhoods, where people say, “They don’t build ’em like they used to.”

It is a superior product for residential construction.  For plaster.  For mortar.  For stucco.  Even for coatings.

Longevity in masonry comes from lime.

Brick and Lime.  It’s how America was built.

My name is Jonathan Arn, co-founder of Brick and Lime.  Stay with me, and together we will learn more about lime and how to use it in today’s world to solve our problems in the construction and restoration of our homes.

Brick and Lime provides masonry construction and restoration services, including pointing, structural walls, stucco, plaster, chimneys, and fireplaces.  We use all kinds of mortar and masonry units, depending entirely on what the situation requires.