By: Ed Pon
July 28th, 2021
As a restoration architect, I have often said that matching brick is one of the most difficult tasks to perform when restoring brick masonry. Brick matching is successfully accomplished when new brickwork is indistinguishable from existing brick work. Let’s face it, no building owner wants to see a patchwork of mismatched brick on their building.
Infilled window is a reasonably good match with careful attention to matching the mortar as well as the brick blend.
This patch is not a good match. The lightest brick is much too light and the darkest is much darker than the darkest brick in the blend. It may have been better to use only the medium-colored brick.
Brick has been used for thousands of years. But most buildings that we are working on now are perhaps only one or two hundred years old. So, we are trying to match brick that was manufactured using relatively modern techniques. Brick is manufactured from natural materials which are blended from sandy clay soils or from crushed shale. Manufacturing techniques of the last 40 years use more precise computerized batching, mixing, and firing so a higher degree of consistency can now be achieved. The brick manufacturers will make the case that batches from different years, will vary and may not be an exact match, but can be made a close match. Bricks from older buildings were manufactured with less consistency so there is greater variation of color and texture. Old brick is also weathered and soiled, making it even harder to match with new brick. That being said, there are many modern bricks that are manufactured to try to mimic the appearance of weathered old brick.
When we go about the process of matching brick, we must look at the brick and the mortar together. The factors we need to consider for a good match are:
- Mortar color and texture
- Mortar joint profile and size
- Brick color(s) or range in a blend
- Brick size
- Brick texture
Brick matching is very difficult because we are usually trying to match weathered old brick with newly manufactured brick. Unless we start the search for matching brick in the early stages of a restoration project, we are often at the mercy of what is in stock. Brick showrooms, such as Belden – Tri State, have a vast selection of hundreds of bricks representing dozens of brick manufacturers throughout the country. They are likely to have the closest match available, like picking paint swatches at your local paint shop. Brick sample boards are made up of ½” profiles of actual face brick that is glued on to Masonite display boards to look like tiny brick walls, complete with carrying handles.
Even when a good match is found, there may be only a limited number of brick available within that batch. And unlike your local paint store, a custom brick color cannot be mixed on the spot. For most restoration projects you will only need a few thousand bricks. Brick manufacturers will run certain color bricks for a limited time and only during a certain time of the year. Even if a designer, contractor or owner finds the perfect brick, it may not be available for several months. For a special out-of-sequence manufacturing run, the minimum brick order is usually about 30,000 units. And it may be months before that brick is run. It is important to begin the search for brick very early in a project, sometimes even before the project is even sent out for bid, the brick can be reserved and stored before it is needed on the project. It is also a good idea to order an extra 5% to 10% of additional brick backstock for the next façade project once a brick match has been found.
Unlike brick, mortar matching can be dialed in with great precision. If a sample of existing mortar is cut out and sent to a company, like SpecMix, a nationwide network of cementitious product distributors can analyze it and send 4 or 5 custom-matched mortar samples in little 4” plastic channels for review and selection. Once a color is selected, SpecMix can send you a small 10 lb. bag of mortar so you can install your own physical mockups. SpecMix pre-packaged mortar mix uses computerized batching equipment and comes complete with sand, cement, and pigment so you add only water; this helps to facilitate a more consistent product.
In order to start the brick matching process, the make-up of the existing brick should be studied. It is common for brick facades to have a “blend” of more than 1 color; some have 3 or 4 different hues of similarly colored bricks. Matching 3 or 4 bricks is part of the restoration effort. A typical 100 brick area can be a good representation of a brick sample; within the area, a count of the number of bricks of each color will help determine the percentage of each color.
It is a good practice to match clean brick. Removing years of soot and air pollution can drastically change the appearance of brick. And even if you are not planning to clean the entire building any time soon, it is a good idea to make every effort to match to clean brick, and your patch will then blend with the old brick. This is standard practice when matching brick on a building that is subject to a Landmarks Preservation Commission review.
If a perfect brick match is required, “harvesting” a brick from a less visible area of the building, (such as a roof bulkhead or an obscure corner in the rear of the building) can be a solution.
When matching the brick-and-mortar assembly, it is important to be familiar with the concept of “simultaneous contrast.” The idea is that an object will appear lighter against a darker background, and conversely, the same object will appear darker against a lighter background. In my experience when matching mortar against a dark colored brick, I have found that it is better to go with a slightly darker shade than a lighter one because a slightly lighter colored mortar will contrast more with the brick and appear to stand out more than a slightly darker colored mortar, which tends to recede and appear muted, especially when viewed from a distance.
Example of the effect of mortar color against brick color (although there are two different brick color blends). The light-colored mortar on the left contrasts greatly with the brick, a much more pronounced effect than the right panel where the mortar does not contrast as much with the brick.
The timing of a tooling or finishing application of the mortar joints also affects the appearance of the mortar. Striking or tooling the mortar too soon after it is applied, tends to brighten the finish and make the joint texture appear smooth. Waiting a few minutes longer to strike the joint after the mortar has begun to set and dry, will yield a slightly rougher finish to the joint, and providing a slightly darker appearance in bright sunlight.
One final tool we have in the quest to successfully match brick, if all else fails, is to apply a pigment (stain) to the brick face. Unglazed brick is a fairly porous. Paint or other surface coatings should generally not be used on brick because they are typically not permeable; moisture can become trapped and cause the paint to blister and debond from the surface of the brick as water vapor is migrating from the core of the brick. Mineral silicates such as Keim and Conproco Mp3 are fully permeable, colorfast, and chemically bonded to the brick substrate; the coating is a durable option for surface coating.