The character of many of our historic buildings owes much to the quality of their brickwork.
Hard as a brick" doesn't mean indestructible. Restoration work on historic buildings often involves fixing bricks that have been damaged in various ways. Some are simply broken from impacts. Others are disintegrating because of improper maintenance. One common maintenance problem is using the wrong type of mortar when repointing (replacing deteriorated joints between bricks). Because they were fired at lower temperatures than modern bricks, pre-20th-century bricks are relatively soft. They absorb and release water, expanding and contracting in the process. The lime mortar used with them was even softer, so it was able to cushion that movement. Periodically, the mortar deteriorates and has to be replaced. Using more rigid, less porous cement-based mortar traps water inside the bricks and keeps them from expanding. The resulting pressure slowly crumbles the constrained bricks.
Another type of problem is that bricks produced 100 years ago were fired in coal-fueled beehive kilns with uneven heat distribution. Under-heated bricks, which were softer and less durable, were set aside for interior use. Sometimes, these softer bricks were mis-categorized and mistakenly used on exterior walls, where they could not withstand the assaults of weather. Regardless of what caused the deterioration, building restoration specialists can choose from four techniques for fixing historic bricks.
If a brick is badly deteriorated, the best solution is to replace it, according to John Speweik, an historic-masonry specialist. "You have to make sure that you have something else to put in there that matches," he says, emphasizing that the replacements must match in performance characteristics as well as appearance. Speweik's first strategy is to search the site for available bricks from the original construction. For example, he might take them from out-of-sight places such as foundations or attic walls.
The potential problem with harvesting bricks from interior walls is that they may be the softer bricks that were under-heated in the kiln. Sometimes, these are called "salmon bricks" because of the lighter, pinkish color they had when new. Over time, that distinctive color diminishes, making it very difficult to distinguish the softer bricks from harder ones that were suitable for exterior use. "Generally, you can tell by clinking two bricks together," says Speweik. "If it's a high-pitched ringing sound, they're evenly fired through and that tells you they are a harder brick. If you clink two bricks together and they have a dull clunking sound, then they probably aren't going to survive very well on the exterior." He cautions that the test is not completely reliable, however. "There really isn't anything you can do to absolutely ensure that it's not an interior brick. It's a risk you take."
If original bricks are not available, an antique brick supplier may be able to provide similar ones. But that process can be tricky. "There were many, many brick makers all over the country. Getting an exact match is very difficult because you have to find something specifically in that area," says Mike Gavin, co-owner of Gavin Historical Bricksof Iowa City, IA. He asks potential clients to e-mail his company a digital image of the brick to be matched, along with the dimensions. "We look at our selection of products we've reclaimed all over the country. We know where we get the brick, and we usually know the general history and age of the brick that we reclaim," says Gavin. "If we think we have a good match, we send them a sample of our brick so they can put it right up to their existing project for comparison."
It may not be possible to locate matching bricks if the originals are an uncommon size, color or texture. In that case, reproductions may be ordered from one of the few producers that still use beehive kilns. "That's typically a costlier option, just because you set up for a small production of bricks," says Gavin, who sometimes contracts with a custom brick maker. "We have had a lot of good luck, especially when it's a real unusual texture and that's what's most important to them."
Another alternative is to purchase new sand-struck bricks, which have a rough surface texture and may be designed to have irregular edges and corners. "Old bricks were made in molds lined with sand, and the sand helped to release the clay when they were hard enough to flip out of the mold," explains Speweik. "There are companies that make sand-mold brick today. Those tend to match historic bricks better."
When attempting to introduce non-original bricks into an historic structure, it is important to match not only the size and appearance of the existing bricks but also their functional properties. In particular, bricks manufactured using more modern techniques may be harder and less porous. Those used during the 18th and 19th centuries absorbed 20 to 25 percent of their weight in water, although under-fired bricks could absorb 35 percent of their own weight. By comparison, early 20th-century bricks typically absorbed no more than 10 percent of their weight in water. Inserting incompatible bricks into an existing wall prevents the façade from operating as a coherent structure.
"Repairing bricks is cheaper, and you probably can do a better job of matching what's on historic buildings with repair mortar, as opposed to buying new brick," says Dennis Rude, president of Cathedral Stone Products of Hanover, MD. His company formulates brick repair mortar to match the color and texture of existing masonry.
Original bricks may be found on historic properties in easily overlooked places such as walkways, lawn borders, rubbish piles or footings laid to support modern garbage cans. Photo: courtesy of U.S. Heritage Group