Choosing Between Modern Lime Mortar and Traditional Portland Cement Could Make or Break Your Historic Brick Repointing Project
When it comes to brick repointing projects, the choice between lime mortar and Portland cement isn’t just about preference—it’s about preserving the structural integrity and longevity of your masonry. The argument on whether to use lime mortar vs portland cement is actually a very important one and using the wrong mortar can cause irreparable damage to historic brick. Understanding the fundamental differences between these materials is crucial for homeowners and contractors alike.
Understanding the Historical Context
Up until 1871 in America, nearly every masonry building was made using lime mortar. Before the 1870s, when portland cement mortar became commercially available, most masonry structures—the Egyptian pyramids included—were built using only lime and sand. This historical perspective is important because with historic houses, the correct mortar is often lime-based, which is what was used when the house was first built.
The shift to Portland cement occurred during the Industrial Revolution, when with the ready availability of portland cement, a material so hard and so impervious to water that it is used to plug leaks in basements, masons abandoned time-consuming lime-based mortars, which set so slowly that no more than seven courses could be done in a day.
The Critical Differences: Breathability and Flexibility
The most significant difference between lime mortar and Portland cement lies in their breathability and flexibility characteristics. Historic masonry is not a waterproof material. It takes in moisture and lets it back out again as does the lime mortar. But portland cement is not breathable. Repointing with portland cement will trap moisture in the wall and cause efflorescence and premature failure of the brick.
Lime mortar, on the other hand, is more accommodating, and its lower compressive strength high flexibility allows the historic masonry units to expand and contract without being damaged. Lime mortar also allows water vapor to pass in and out of the joints, which means that moisture does not get trapped in the brick or the stone.
The Sacrificial Element Principle
A fundamental concept in masonry restoration is that mortar is the sacrificial layer. In a nutshell, for a stone foundation or a historic brick wall, the mortar should be the sacrificial layer. This means you always want your mortar to be weaker than your masonry units for this reason.
When Portland cement is used inappropriately, Portland cement mortars are unable to wick water out of the walls, so water gets trapped and instead escapes through the historic stone or brick. This damages the masonry units as the water pressure builds until the face of the brick or the stone pops off, exposing the inside of the unit and making it more vulnerable to continued deterioration.
Modern Applications and Benefits
Today’s lime mortars offer several advantages that make them increasingly popular for both historic preservation and new construction. Lime mortars are preferable to Portland cement mortars for repointing historic masonry: Lime mortars are more permeable by water. Water passing through lime mortar will dissolve a small portion of the lime and then will deposit it in hairline cracks as the water evaporates. Lime mortars expand slightly during setting, and resists shrinkage which causes cracking. Lime mortars are more durable than generally recognized.
Modern builders are increasingly turning to lime mortar as a sustainable and environmentally friendly alternative to cement-based mortars. Lime mortar’s low embodied energy, ability to absorb carbon dioxide during curing, and compatibility with natural materials align with contemporary green building practices.
When to Use Each Material
The choice between lime mortar and Portland cement depends largely on the age and construction of your building. Best practice is to use a mortar similar to the mortar that is in the wall originally. If you have a lime mortar, you should continue using a lime mortar. For buildings constructed before 1940, lime mortar is typically the appropriate choice.
For newer construction with modern, harder bricks, Portland cement may be suitable. However, a softer mortar mix is required for older properties including the 1920s. The cement we use these days is a much harder product than in days of old, so Lime added to Portland cement and sand will ensure a softer mortar. If you just go for a modern mix you are likely to lose the exterior face of some of your bricks, as with cold, heat and humidity the bricks do better with a mortar that as soft, if not softer than they are.
Professional Expertise Matters
Given the complexity and importance of choosing the right mortar, professional expertise is invaluable. Companies like Ageless Masonry, serving Nassau and Suffolk Counties on Long Island since 2003, understand these critical distinctions. We’ve been providing homeowners in Suffolk and Nassau Counties on Long Island, NY, with the highest-quality paving and masonry services since 2003. Customer satisfaction is our top priority. When searching for brick repointing near me, it’s essential to work with contractors who understand the historical context and material compatibility requirements of your specific project.
Great service always begins and ends with experienced and friendly professionals, which is why you can count on an owner to be present for every aspect of your job. We aim to not only meet your needs, but also to exceed your expectations!
Making the Right Choice
The decision between lime mortar and Portland cement isn’t just about following trends—it’s about preserving your investment and ensuring the longevity of your masonry. Take good care of your brick and stone by choosing the right mortar when you need to make repairs and your historic masonry will be protected for centuries to come, use the wrong mortar and in only a few years you may end up with disintegrating brick that is extremely difficult to replace.
Whether you’re dealing with a historic brownstone or planning new construction, understanding these material differences will help you make informed decisions that protect both your property value and architectural heritage. The key is matching the mortar to your specific masonry type, building age, and environmental conditions—decisions best made with professional guidance from experienced masonry contractors.