Masonry Repair for Millcreek Chimneys

Why elevation makes the damage worse

Millcreek climbs from the valley floor to the foot of the Wasatch, and the higher ground swings across freezing more times per winter than the flats do. A bench chimney can freeze overnight and thaw in afternoon sun repeatedly through February. Every one of those cycles takes water that has soaked into brick and mortar and expands it by roughly a tenth of its volume. Brick has no give. The face pops off in flakes, which is what spalling is, and once the face is gone the brick behind it drinks water even faster.

Shaded elevations get it worst because they never dry out between cycles. If one side of your stack looks far rougher than the others, that is usually the reason rather than bad brick.

Where the water gets in first

• The crown. Many mid-century chimneys here were finished with a thin mortar wash instead of a cast crown with an overhang and a drip edge. Mortar wash cracks within a decade and then funnels water straight into the top of the masonry.
• Open mortar joints. Lime-based mortar is meant to be the sacrificial part of the wall, and after seventy years it has done its job and needs replacing.
• Flashing at the roof line. Counter-flashing that was face-nailed and caulked rather than cut into a mortar joint will let go, and the leak shows up as a ceiling stain that gets blamed on the roof.

Repairing rather than replacing

Not every damaged chimney needs to come down. Repointing the affected courses, casting a new crown with a real overhang, swapping spalled units and correcting the flashing solves the majority of what we see in Millcreek. We will tell you when it has gone past that: when the stack has lost enough section to be unsound, or when the brick is so far gone that repointing has nothing solid to key into. A rebuild from the roof line up is a real job with a real price, and it should be argued for with photographs.

Mortar has to match

New mortar that is harder than the surrounding brick does not protect the wall, it destroys it. The joint becomes the strongest part of the assembly and the brick face takes the stress instead. On older Millcreek masonry we match the mix to what is already there rather than reaching for a bag of the strongest thing on the shelf.