Traditional lime mortar wicks water out of bricks and flexes as thick masonry walls expand and contract. Modern cement mortar sets faster and is stronger, but its rigidity and impermeability prevent natural movement and water dissipation. Consequently, building movement causes severe cracking across wall faces, while trapped moisture freezes, expands, and hollows out historic bricks behind rigid mortar shells.
After World War II, rising labor costs prompted builders to replace small structural bricks with concrete blocks, which cover seven times the volume much faster. As demand collapsed, the 1970 Clean Air Act mandated strict emissions controls. Because Chicago common brick manufacturers still fired bricks using primitive scove kilns rather than enclosed ovens, they could not afford the necessary upgrades, ending domestic common brick production by 1981.
As skyscrapers adopted steel skeletons—exemplified by the later wing of Chicago's Monadnock Building—brick ceased being the primary load-bearing element. Instead of carrying structural weight, bricklayers were relegated to enclosing steel frames for fireproofing or applying exterior brick as decorative veneer. Once relegated to a decorative material, brick was freed from structural requirements, allowing modern architects to treat it as an aesthetic statement rather than a foundation.
After the 1871 Great Chicago Fire, the city urgently needed to rebuild. Although local glacial clay was full of stones and limestone that produced pitted, soot-absorbing bricks mocked nationally as the country's ugliest, brickmaking machinery enabled manufacturers to press 36,000 bricks per hour. Driven by intense post-disaster urgency, Chicago rebuilt itself using whatever clay lay right beneath its feet, regardless of aesthetic flaws.
Because Chicago clay only produced rough common brick, architects restricted it to hidden interior backings and unseen side walls. To present an attractive exterior, developers imported higher-quality face brick made from diverse regional clays—such as fine red clays from St. Louis or iron-spotted fire clays from Ohio and Pennsylvania. This created Chicago's stark visual contrast between elegant street facades and raw common-brick sides.
Chicago's Monadnock Building, the world's tallest pure masonry skyscraper, reached 16 stories without steel by building load-bearing walls six feet thick at the base. To achieve its smooth, unornamented curves without chiseling on site, manufacturers crafted hundreds of specialized brick molds and meticulously regulated kiln temperatures to maintain uniform color, illustrating the immense material precision required to build skyscrapers exclusively out of brick.