The North Classroom Building at Denver's Auraria Higher Education Center has an interior glass block corridor wall that is 1 1/2 city blocks long and 2 1/2 stories high. Inside and out, the building uses 59,000 12x12-inch and 5,000 8x8-inch glass block, making it the largest glass block building in the United States. The large glass block corridor wall created many design and construction difficulties. Glass block's nonuniform load-bearing properties allow it only to support its own weight--and even that has limits. Glass block panels can't be larger than 10x16 feet without further support. For this reason, the glass block walls of the North Classroom Building were divided into 10x12-foot panels. T-section steel framing was used to support the panels. Four types of glass block were used to build the back wall of the gallery, which fronts several types of rooms. The clear, patterned, reflecting, and translucent block provide view, light, privacy, and architectural continuity. To lay the glass block straight, the masons attached magnets to the vertical steel support frames, tied a line between the magnets, and laid the block to the line. Joints had to be kept between 1/4 and 5/16 inch wide. They used Type S portland cement-lime mortar. On the front side, they struck the mortar with a jointing tool, then wiped it with a wet sponge to make it smoother.