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.