Chicago Common Brick: What It Is and Why It's Soft

What is Chicago common brick? It is the plain, unglazed brick that makes up the body of most older Chicago masonry walls. You often see it on the sides and backs of buildings, sometimes behind a nicer face on the front. It is rough, a little uneven in color, and it was never meant to be fancy. What matters for an owner is simple: this brick is usually softer than the modern mortar and patching materials that get put on it.

We use the term the way owners and masons use it on the job. We are not going to tell you where it was made or when, because we can't source that here. What we can tell you is what it does when someone repairs it wrong, and how to tell if that has happened to your wall. This page sits inside our guide to Chicago building types, and our masonry crew repairs it.

What does Chicago common brick look like?

Look at the side wall of an older two-flat, or the back of a building, and you will usually see it:

• Plain faces. No glaze, no pattern, no fancy texture.
• Uneven color. Reds, browns, and sometimes pinks and oranges in the same wall.
• Wide, hand-struck looking mortar joints. Often lime-colored or gray with age.
• Bricks that read soft. A key or a screwdriver tip will mark the edge of a joint, and weathered faces can powder at the surface.

Many Chicago buildings put a better looking brick or a stone on the front and common brick on everything else. That is why a greystone can have a limestone front and plain brick sides, as we describe in what a Chicago greystone is. If you want to tell your common brick from a smooth, uniform face brick, see common brick versus face brick.

Why is old Chicago brick considered soft?

This is the part we can speak to directly. When we repair old walls, we find that the brick is often softer than modern portland-heavy mortar. That mismatch is the reason the National Park Service says repointing mortar must be softer, measured by compressive strength, and more vapor permeable than the masonry units, and no harder than the original mortar (NPS Preservation Brief 2).

The brief is blunt about why. In a wall, stress should be relieved by the mortar joint, not by the brick. The joint is the sacrificial part. If the mortar is stronger than the masonry, it can cause cracking and spalling in the units that cannot be easily repaired (NPS Preservation Brief 2). The same document says hardness or high strength is not a measure of whether a mortar is appropriate.

In plain words: you want the mortar to wear out before the brick does. Mortar can be redone. A brick face can't.

What happens when hard mortar goes on soft brick?

Two things, and both come from moisture.

First, water moves through a wall. When the mortar is less permeable than soft brick, the moisture and dissolved salts move out through the brick instead of the joint. Salt crystallizing inside the brick can make the face spall or flake off (NPS Preservation Brief 2). The National Park Service shows trapped moisture eventually popping the surface off bricks behind hard portland mortar.

Second, the face breaks down in freeze and thaw. A saturated brick that freezes can lose its surface, and salt crystallization is another cause of the same damage (NPS Preservation Brief 2). Chicago winters hand every exposed wall plenty of chances.

For the full story on this mistake, see the mortar mistake that ruins Chicago brick.

How can you tell if your common brick is soft?

You can look. You can't test it properly yourself. Here are the signs:

• Mortar that scrapes out with a key. That's the mortar, not necessarily a problem with the brick.
• Brick faces that flake, peel or powder, especially near the ground, under windows and at the roofline.
• A hard-looking repair beside crumbling brick. That mismatch is the tell.
• White powder or crust on the surface. Efflorescence is salt moving out of the wall. It usually isn't harmful on its own, but it tells you water is getting through (BIA Technical Note 23A).

A mason can check the brick, the old mortar and the new patches and tell you what mix to use. That is a site visit, not a photo job.

What mortar should go on old Chicago brick?

The honest answer is: whatever is softer and more permeable than the brick and no harder than the original, which is to say a mix matched to your wall. The National Park Service points to lime-rich mixes for historic masonry, and says old mortar should be removed to a depth of two to two and a half times the joint width, with hand chisels being least damaging (NPS Preservation Brief 2).

That means the contractor should be able to tell you the mix and why. If the answer is "whatever we use on everything," that is a red flag. Our Chicago tuckpointing guide covers mortar and technique in depth, and our two-flat explainer covers where this brick shows up on the most common Chicago building.

Does repairing common brick need a permit?

Usually, yes. The City lists tuckpointing under the Express Permit program as masonry maintenance and repair (City of Chicago), and masonry work in clay brick is covered by the City's mason contractor license (City of Chicago). The only masonry no-permit repair is a small in-kind replacement. Rules change, so confirm with the Department of Buildings.

The City also expects the exterior to be kept in good repair, with masonry joints weather resistant and water tight (Title 14X). Soft brick that is losing its face isn't just ugly. It stops keeping water out.

What to ask a contractor about old brick

1. What mortar will you use, and how do you know it's softer than my brick?
2. How will you remove the old mortar, and to what depth?
3. Will you grind or chisel? If grinding, how do you keep from cutting the brick edges?
4. If bricks have spalled, which will you replace and which will you leave?
5. Who is pulling the permit?

If your wall has a hard repair next to flaking brick, or you just want a straight answer about what mix belongs on your wall, we'll take a look and tell you.

Common questions

This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.