From the sidewalk at 100 East 22nd Street, the Pillsbury Mansion looks like it was carved from a single block of stone. It wasn’t. Behind every inch of that limestone is a hidden construction system of steel, brick and clay tile, and two engineering visits, one in December 2023 and one in March 2025, give us a rare look at how it has aged. The reports read like a diary kept by a building that has spent more than a century being rained on, frozen and thawed.

What is the Pillsbury Mansion’s wall actually made of?

The 2023 structural review describes the facade as 4-inch-thick Bedford limestone, a type of Indiana limestone, laid in an ashlar pattern of neat rectangular blocks. Behind that thin stone skin sits a multi-wythe clay brick wall, and steel strap ties hold the limestone to the brick. Inside, the floors are cast-in-place concrete pan-and-joist slabs with clay tile between the joists, and the roof is carried on steel beams with more clay tile between them. It is the same hidden skeleton we explored in why the mansion was built like a skyscraper, seen now from the engineer’s side.

One small note on dates. The engineers write that the house was built in 1912; elsewhere in our account of building the mansion the story is longer, with construction starting in 1912 and the house finished in 1916. Both are right about different moments in the same project, so we leave the two dates side by side.

How does a steel strap tie make stone crack?

This is the heart of the report. When water reaches a steel tie, the steel rusts, and rusting steel expands. The expanding metal pushes against the stone around it until a piece spalls off the face. The engineers saw isolated spalls like this on every side of the building. Separately, water that soaks into the limestone itself freezes in winter, expands again, and cracks the block. And when a tie fails altogether, the report says, the stone is left with little or no support, which is how blocks end up shifting out of line.

In Minnesota, that is a hard cycle to escape. A wall can be wet and frozen dozens of times in a winter, and the reviewers warned that more spalls will appear where corrosion is hidden and has not yet broken the surface.

Why did the portico take the worst of it?

The north-side portico showed the most serious deterioration in the 2023 review. Mortar had failed at the columns and the parapet wall, letting water into the clay-brick backup, and freeze-thaw damage there had, in the engineers’ words, significantly reduced its load-carrying capacity. The westernmost column was the worst, with severe deterioration and noticeably displaced limestone. Parapets and top-floor walls fared poorly too, because the third floor takes the most weather. Some of the mortar looked like a patchwork of original joints and later repairs, and the reviewers noted that some of those repairs may not be compatible with the old masonry. That matches the guidance in the National Park Service’s Preservation Brief on repointing mortar joints in historic masonry buildings, which stresses matching the mortar to the original.

What else did the engineers find?

The inventory is wonderfully specific. Vines had grown thick enough in places to hide the stone. In the sub-basement boiler room, steel beams showed corrosion throughout the section the engineers could see. The two flat roofs, with built-up membranes, were in poor shape, while the slate gabled roofs looked fair to good from the ground, and the steel roof framing seemed sound. The terra cotta chimneys were fair, with failed mortar and some cracked tiles. (The report counts three chimneys in its introduction and four in its results, a discrepancy we are leaving exactly as written.) A stockpile of spare terra cotta units sat in the sub-basement, likely left over from an earlier repair program.

Two details are pure time capsule. The elevator shaft on the north side is not original; it was added in 1994, during the remodeling for BLIND Inc., and is clad in a modern synthetic stucco. And along the south and east property lines, the stone retaining wall had about six failed bollards and some 35 feet of missing railing, reported to be the result of vehicle collisions at the adjacent intersection. Mansions, it turns out, also have to survive traffic.

What did a second engineer say in 2025?

A structural engineer who visited in March 2025 read the earlier report and walked the building. His letter begins with a verdict that surprised no one who loves old buildings: it “has passed the test of time” and is relatively good for its age. The main culprit, he wrote, is water getting into the walls and basement, and the first job is to fix roof leaks, flashing and parapet caps and to point downspouts away from the foundation. After that he described the repairs as ordinary work for an old building: shore the small portico roof, fix cracked stones one at a time with grout or epoxy, replace broken ones, and replace the steel ties if they have rusted. He added that care is needed when removing stone.

These documents describe the building as it stood on the dates of the visits, not today. What they give us is the physical record behind the story: the mansion that the Splendors pages celebrate is held up by hidden steel, tile and brick, and it is protected by the unglamorous work of keeping water out. For more on why that matters, the National Park Service’s page on the National Register of Historic Places explains the program that recognized the Pillsbury Mansion in 1974.

How can you see the stone for yourself?

The best way to appreciate all of this is to stand on 22nd Street and look up. The carved lions at the door, the parapet friezes and the ashlar blocks are all there, and you can go inside on a guided visit. See plan your visit and experiences and tours for current options, or climb aboard a Minneapolis Trolley Tours ride that departs from the Club. Missed the roof story? Read what an engineer found above the skylight.

Keep reading: How Do You Spend a Gilded Age Weekend in Minneapolis?

Keep reading: How Do You Put a Modern Fire Sprinkler System Into a 1916 Mansion?