Lime Mortar and Hardscaping, FAQ Friday with Randy Ruth

When it comes to hardscaping with masonry, I am all for mortarless construction. The beauty of a well built dry stacked stonewall or paver application creates a natural aesthetic on any property. Often times however, there is a need or desire for a more permanent structure requiring mortar. Traditional brick garden walls in a Flemish bond pattern are a particular favorite of mine. The truth is hardscaping options are endless with so many creative ideas for an architect or master mason. Variations in brick bond patterns can come up abruptly with changes in architectural style creating such visually stimulating surround that once immersed, one may find themselves in a peaceful wholesome setting. I find myself not feeling this way in locations recently constructed but in older, aged locations, where there is a bit more character. This character comes from the details in construction.

With mortar taking up about 20% of  the surface area on a wall, it is no surprise that mortar detail has a subtle yet powerful effect on the visual appearance of a masonry wall. In the construction of modern brick walls, Portland cement sticks tenaciously between the bricks, with characterless mortar joints. The two most prevalent types of mortar joints I see are concave and grapevine. While the concave mortar joint is meant to keep a watertight seal between the brick, it looks out of place. Rather it would be happier on the façade of a modern home, office building or utilitarian structure. The grapevine mortar joint style might be a romanticized take on old historic brick jointing that is often abused in modern construction but is not as aesthetically displeasing.

Despite my opinions on joint profiles, it’s the overall appearance that a modern Portland cement causes a hardscape wall to have. Unsightly control joints and modern joint profiles are a direct result of mortar used on a hardscaping project. The use of lime-based mortar can counteract such unsightly details and can be truer to the envious historic gardens of yesteryear in aesthetic quality.

Construction of hardscaped brick walls do not need to have control joints when lime is employed as the primary binder in lieu of Portland cement due to lime’s natural flexibility and free lime content which permits autogenous healing of micro-cracks. The use of lime in new construction is also “green”. The carbon footprint of using lime as a primary binder reduces co2 emissions by as much as 80% when compared to Portland cement. This reduction in emissions represents a greater step forward toward sustainability in our built environment. The breathability of lime mortar also promotes the idea of free flowing and natural earthen feelings associated with hardscaped locations. When our spaces work with moisture and process water rather than trying to trap it, a harmony is produced. This can help bring into sync the man built environment with the natural growing environment of an outdoor space.

FAQ Friday with Randy Ruth

Hooray, Today is Friday! Another rainy weekend will be upon us here in Pennsylvania, but now it’s time for another FAQ Friday with Randy Ruth. Today’s question is another very common question on the use of lime mortars vs. cement. After you finish reading please visit our new facebook page and “Like” us…

• Q: Could I perhaps use cement and sand?  What is the advantage of using lime on old stone structures
• A: You should not use only cement and sand for a variety of reasons, the first being that in today’s mortars, lime adds workability and plasticity to the Portland cement mortars. Without lime in the mix or proprietary additives, the cement and sand mortar will have extremely poor workability. Secondly, modern-day cement is much different than early cement or lime, it is very hard, dense, vapor impermeable, and brittle. Cement can trap moisture inside the wall and erode the mortar behind the repair mortar, this can cause further unseen deterioration and masonry unit (stone, brick, terracotta) deterioration, thus resulting in a delayed and much larger/costly masonry repair.

The advantage of using an appropriate lime mortar on old stone structures deals with compatibility. There is a rule of thumb when approaching a restoration project and that is to repair in kind with like materials. By following this approach an individual can avoid unforeseen problems associated with trying something “new and improved” when there is such a well over 2,000 years of lime building history. There have been a number of studies done around the world on historic structures that conclude that even a small amount of Portland cement added to a lime mortar mix, can cause detrimental damage to the adjacent masonry and historic bedding mortar.

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