Lime Technology & Historic Preservation

Our focus at Howard Hall Farm Restoration Group is on the preservation and restoration of historic architectural elements through the use of lime mortar masonry. This can encompass everything from preserving stone and brick structures to plastering ceilings and walls.

Visit our contact page if you would like to hire Howard Hall Farm Restoration Group for your next project. We offer a variety of specialized services relating to this specific branch of historic restoration:

MORTAR ANALYZATION AND MATCHING

Creating the best lime mortar mix for a project is extremely important. Matching the original mortar recipe ensures that the work we do helps to preserve the structure and guard against any further deterioration. We try to make our mortar as historically accurate as possible to create a close visual match between the repointed brick or stone and the original portion of the building.

PROVIDING LIME TINTS AND FINISHES

Lime tints can provide a great alternative to paint. You can achieve a luster and depth of color that just isn't possible with traditional paint methods. Lime plaster finishes also give texture and richness to any surface. At Howard Hall Farm Restoration Group, we mix our own tints using a variety of historically accurate ingredients to obtain an authentic look in your home, both indoors and out.

REPOINTING CHIMNEYS, FIREPLACES, & BRICK OR STONE WALLS

Many of the projects that we are called in to work on involve the correcting of past mistakes. The most common of these mistakes is the use of Portland cement in the place of lime mortar to make repairs to brick or stone structures. Portland cement can do permanent damage to historic elements. It does not breathe in the same way that lime mortar does, leading to moisture retention and the creation of cracks during the freeze-thaw cycle. It is also brittle and inflexible, which means it cannot move with a building as it naturally settles and shifts. Without this flexibility, brick and stone can break and crumble.

PLASTERING WALLS AND CEILINGS

Before drywall, walls were made using wood lathe that was then plastered over. Preserving this historic method of creating a wall is one of our specialties. While we might use metal mesh lathe instead of splitting hardwood lathes by hand, we still employ the same skills and techniques required to accurately mix and apply lime plaster to walls and ceilings. This method allows us to recreate those peculiar architectural elements, such as rounded walls or decorative details, that are often present in historic buildings.

CLASSES

We know that it is becoming increasingly difficult to find a craftsman skilled in historic lime mortar masonry techniques. To combat this, and to allow homeowners to become more active in their own restoration projects, we hold classes on lime mortar and its many applications in our learning laboratory in Athens, NY.

We are not currently offering any classes at this time, but please check back often or sign up for the Howard Hall Farm Restoration Group mailing list to learn when we will be offering classes again.

APPRENTICESHIPS

We are currently looking for local lime apprentices interested in gaining on-the-job experience in the lime mortar arts. For more information about when and where these apprenticeships are available, please send us an email to receive more information about our apprenticeships.

Use in Art

One of the earliest examples of lime plaster dates back to the end of the eighth millennium BC. Three statues were discovered in a buried pit at Ain Ghazal in Jordan that were sculpted with lime plaster over armatures of reeds and twine. They were made in the Pre-Pottery Neolithic period, around 7200 BC. The fact that these sculptures have lasted so long is a testament to the durability of lime plaster. ^[1]

Use in Architecture

Some of the earliest known examples of lime use for building purposes are in early Egyptian buildings (primarily monuments). Some of these examples in the chambers of the pyramids, which date back to around 2000 B.C., are still hard and intact. Archaeological digs carried out on the island of Malta have shown that in places like Tarxien and Hagar, lime stucco was also used as a binder to hold stone together as well as for decoration at sites dating back as far as 3000-2500 B.C. At Tel-el-Armana, a large pavement on brick was discovered that dates back to 1400 B.C. It was apparently the floor of part of the harem of King Amenhoted IV. ^[2] Ancient Chinese used Suk-wui(the Chinese word for slaked lime) in the construction of The Great Wall of China.

Misconceptions

There are a lot of misconceptions surrounding the definition of what is actually a lime plaster. Lime Plaster refers to a mortar using only pure lime as a binder and sand as an aggregate. Too often, common mortars made out of lime, cement, and sand are improperly called lime plasters simply because they include some kind of lime. The correct name for such a product is stucco, cement stucco, or lime-based stucco. The addition of cement to lime dramatically changes the physical, mechanical, and chemical properties of the lime by reducing its elasticity, breathability (vapor exchange), and durability as well as altering the color rendering. In fact, lime is commonly added to cement in order to mitigate these properties. Mixing Hydraulic or Hydrated Lime, or both, with aggregates, achieves a true lime plaster. ^[3]

Lime Mortars

Lime-sand only mortars can better accommodate any settling or movement in the wall than cements, which do not adjust to changes around them once they set. Although lime stuccoes and limewashes are more breathable, they also have better water shedding characteristics.

Cement stucco is likely to crack under stress or movement, allowing a route for water infiltration into the interior where it will be trapped. Lime stucco can better adjust to early movements in the building because it does not set fully all the way through immediately, but only as the interior more slowly carbonates. Any tiny cracks that open can be resealed as acidic rainwater enters those cracks and either draws some of the remaining calcium hydroxide into the crack, or as the slightly acidic rainwater partially dissolves calcium carbonate along the edge of the crack, temporarily creating calcium bicarbonate and re-depositing it toward the front of the crack as calcium carbonate again. This self-healing characteristic of lime is well described as “autogenous healing.” ^[4]

Lime Plaster

From Imperial Rome to 11th Century Mayan Cities, lime was used to plaster floors at least as early as 9,000 B.C., and the tradition was continued by our ancestors in Colonial America. The fact that lime plasters, renders, stuccos, and washes have lasted to this day gives building lime an 11,000 year track record that is unmatched. With the renewed interest in green technology, environmentally friendly lime plaster is enjoying new popularity in modern homes.

Howard Hall Farm Restoration Group specializes in plaster restoration, and in using lime plaster as well as conventional plaster products. Whether it is walls, moldings, or specialty details, we have the crew and skills to replicate or create what is required to achieve a spectacular result.

Lime Washes

Interior or exterior, lime wash has been used for centures in this country as a finish for walls. We use all lime compatable tints and apply these in a variety of ways to achieve a variety of effects.

Environmental Impact

The use of lime plaster saves approximately 80% of the CO2 release compared to ordinary stucco. One single residence can save between 5,000 and 10,000 lbs. of CO2 emissions. Each year in the US alone, environmentally conscientious builders are saving several millions of CO2 release by simply avoiding the use of cement-based products, and choosing Natural Hydraulic Lime instead. ^[5]

Safety Issues

Lime is an extremely caustic material when wet, with a pH of 12 (Lime becomes pH neutral when carbonated). Protective goggles and gloves should be worn at all times. Additionally, protective clothing should be worn where risk of splatter onto bare skin is present.

Clean water should always be at arms length if lime gets in someone's eye or on their skin. Skin can be neutralized with a very mild acid such as vinegar or lemon juice. Repeatedly flush eyes with fresh water for several minutes and consult a physician. ^[6]

Masonry Case Study

Half Timbered Mid-Century Mansion

This important Hudson River house was built of timber with stone in fill, often referred to as half timbering.

In this case, the timbers were dressed with finish boards, but no drip cap. For years the water got behind the boards and in the walls, breaking and cracking the walls. This led to many bad repairs with Portland cement, which only made it worse.

We installed extensive drainage around the building and repaired and replaced much of the rotting timber with masonry. We then pointed and repaired all the walls and installed lead-coated flashing over every board.

Further Reading

The Natural Plaster Book: Earth, Lime & Gypsum Plasters for Natural Homes
Cedar Rose Guelberth and Dan Chiras, 2002

Canaanites (Peoples of the Past)
J. N. Tubb, The British Museum Press, 1998

Building With Lime: A Practical Introduction
Stafford Holmes & Michael Wingate, Intermediate Technology Publications Ltd, 2003