Q. I need to repair the mortar joints on my older brick home that was built in the late 1800s. I’ve seen some horrible workmanship where the mortar doesn’t match at all, and I want to avoid this. How does one match the original mortar? What would you do to make sure the finished repair is nearly invisible? Is this even a realistic goal, or should I just resign myself to ugly mortar joints that don’t match? – Rhonda S., Boston
A. Years ago, I witnessed a real tuck-pointing travesty. Some mason, handyman or DIYer attempted to tuck-point the mortar joints on a brick home, and the resulting mess was almost hurtful to the eyes. Not only was the mortar smeared on the brick, but it also was such a light color that the difference between the old and new was like night and day. It reminded me of a person with a smear of food on their face while eating. You have a tough time looking at her/him from across the table, to say the least.
I feel the question provides an excellent teaching moment. You might be a person who rushes to the internet hoping to locate a video or someone who purports to be an expert on masonry and mortar. You need to step back and think critically for just a moment before you follow that advice. Think about who is the real voice of authority in the field.
When I first started building back in the 1970s, I used to go to the library to learn about building. The library housed one of the search engines of our time: the library card catalog. One day, I was researching for concrete installation information, and I stumbled across pamphlets published by the Portland Cement Association.
I had never heard about associations before – keep in mind I was a mere 23 years old and had very little life experience. Before long, I discovered there were scads of associations that represented building products. These associations are in the business of not only promoting their products but also more importantly instructing how to install and take care of them the best way.
In short order, I discovered the Brick Industry Association and once there was taken aback by its vast library of technical notes about everything you could ever imagine about brick, mortar, flashings, chimneys and so forth. I reached out to the association at the time, and, at no cost to me, two massive binders filled with all of the technical notes publications arrived in the mail. I thought I had died and gone to heaven.
You would do quite well to read two of the Technical Notes publications: Numbers 8 and 8B. Both deal with mortar. You can get them as free PDF files from the BIA website at gobrick.com
Here’s what you’ll discover. There are different types of mortar, and mortar used a hundred years ago is not necessarily like the mortar mix you’d buy today at a building supply business. Many years ago, it was common for bricklayers to just use hydrated lime and sand to make their mortar. Hydrated lime is truly a magical building material.
Modern mortars come in all types depending on the finished design strength of the masonry. It can get very complicated very fast. Suffice it to say that many modern mortar mixes are a proprietary blend of Portland cement, hydrated lime and other ingredients blended for the design purpose of the mortar.
One of the places that masons, handymen and DIYers go off the rails is the sand component of the mortar. Look closely at an older weathered mortar joint in between two bricks, and you’ll quickly notice that you see more sand than you see the actual cementitious powder that binds the sand together. This is very important when you are trying to match the color and look of the mortar.
You need to do some homework and locate the same sand as you have in your existing mortar if you want to get a close color match once the mortar is installed. Think back where the bricklayers of old would have obtained the sand. It was difficult 100 years ago to transport heavy things great distances. Is there a nearby gravel pit that’s still in operation? Do old newspaper clippings talk about local gravel pits that are now closed? Do what you have to do to locate sand that’s the same size and color range as your existing mortar.
If I were helping you as a consultant, here’s the first thing you and I would do to start the project. I’d clean the existing masonry. There’s a good chance the existing house is dirty, so the mortar would be dirty, too. I’d want to clean the mortar, at least on the wall that’s being repaired, so I could see exactly what we must match. You can use a pressure washer for this job, but you need to exercise extreme caution that you don’t damage the brick or the mortar.
Once the brick and mortar are clean and dry, we would need to judge whether the brick masons colored the mortar. It was often done on jobs so the mortar had a tint close to the color of the brick. I’d then mix up a test batch of the mortar using the guidelines from the BIA technical notes No. 8 and allow it to dry for a week or two.
You and I would then use a very, very mild acid wash to dissolve the lime from the sand on the surface to see if we have a match. We need to expose the actual sand particles to see the true finished color of the mortar. With trial and error, we could come close to matching the original color.
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