Keep plants OUT of your mortar joints!

This historic brick wall is an example of beautiful masonry architecture going to waste. The wall in these pictures was built over 100 years ago, it was well built then and still a lasting reminder of good architecture of the time. In recent decades though the wall has been neglected. The mortar joints have been exposed to harsh weather and over time have decomposed.

Stage 1 – Unmitigated deterioration of mortar joints

This wall was built with a lime mortar, but the lime is not alone. There is also sand in the mortar. The lime component of the mortar is, at the time of installation, in the carbonination stage of the lime cycle. About 60 to 100 years later, after significant time and weather has affected the mortar, significant of deterioration become present, a result of hydrated and dissolved calcium hydroixide.

The pictures below show and explain the stages of plant growth and escalating accelerating deterioration. The pictures below start with stage 2, the onset of initial plant growth. But really it all starts with stage one, the slow deterioration of masonry and brick mortar joints over time from unmitigated exposure to the elements.

Stage 2 - Cyanobacteria, fungi, and then mosses grow on top of mortar joints.   In this picture you can see a thin layer of moss has started to grow on top of the exposed mortar joint. This only happens once the mortar joint has deteriorated significantly to the point that there is an inordinately higher ratio of residual sand than lime mortar binder.
Stage 2 – Cyanobacteria, fungi, and then mosses grown on top of mortar joints.
Stage 3 – Leafy seed bearing plants take root.
Stage 4 – Woody root plants take root and cause serious damage. The plants takeover after masonry mortar joint deterioration, damage escalates rapidly. Woody plant roots have the ability to break masonry and concrete and cement apart, and are powerful at breaking building elements apart into pieces.

Stage 5 – Plants have rooted deeply, and worse than just simple vegetative root hairs, actual woody tap roots are breaking apart the masonry wall assembly.

This physical and chemical process of changing states of lime mortar, explains why lime mortar deteriorates over time. It is a natural process for buildings. Ongoing life-cycle maintenance and the deterioration curve is another related concept. We talk about more in other posts and blogs on our website. The big takeaway is that it is increasingly exponentially more expensive to maintain masonry buildings if they are not looked after on a routine basis. Unlike some materials like wood, for example, masonry is on a much larger time scale and can be repointed just a few times per century. Nonetheless it is still good to have a pro mason go through and observe conditions every couple years.

Once conditions go downhill, they start to do further downhill faster and faster. The deterioration curve is nonlinear. That means that things like failing mortar joints allow plants to grow on year, and by the next year the roots of those same plants have gotten deeper into the mortar joints. Because of the roots, now water can travel deeper into the mortar every time there is rain, and so on and so on.

Protect your walls and invest in good maintenance, it will save you a lot of money in the long run. Find a good local masonry contractor, build a rapport and a relationship, hire the contractor for a low cost consultation and make a prioritized plan for maintenance to keep your building in good shape for years to come.