Masonry Repair on Mapleton Chimneys

Freeze-thaw, and why elevation makes it worse

Masonry damage in northern Utah is a water story with a temperature trigger. Brick, block and mortar all hold some water. When that water freezes it expands by roughly a tenth of its volume, and it does that expanding inside pores that have no room to give. Each cycle pushes a fragment of the surface loose. Do it a few hundred times and the face of the brick sheds in flakes, which is the spalling you can see from the driveway.

What matters about Mapleton specifically is the number of cycles and the amount of water available for each one. Sitting higher and closer to the mountain than the middle of the valley, the town gets more snow and holds it longer, so a chimney crown can stay wet under a snow cap for weeks at a stretch while daytime sun and overnight cold cycle it again and again. A crown that would last twenty years on a dry, exposed lot has a much harder life here.

The crown is almost always where it starts

The crown is the sloped concrete slab at the top of the chimney that sheds water off the masonry and away from the flue. A properly built one is cast several inches thick, reinforced, sloped, and has a drip edge that overhangs the brick. What was often built instead is a thin skim of mortar troweled flat across the top. That cracks within a few years, water runs straight down into the chimney's core, and everything below it starts to fail from the inside where you cannot see it.

Stone veneer hides the evidence

A great many of the custom homes here carry stone or cultured-stone veneer on the chimney chase. Veneer looks permanent and it is very good at concealing what is happening behind it. Water entering through a failed crown or an unsealed cap can run down inside the chase for years, rotting the framing and rusting the flue system, while the outside still looks new. When we inspect a veneered chase we are looking at the top, the terminations and the interior, not just the visible stonework.

Flashing is a roofing job people call a chimney job

Where the chimney passes through the roof there should be two layers: step flashing woven into the shingle courses and counter-flashing let into a cut groove in the masonry and sealed. Caulk smeared along the joint is not flashing. It is a two-year fix on a thirty-year problem, and it is the single most common cause of the water stain that shows up on a bedroom ceiling near the chimney.

Repointing, rebuilds, and being honest about which

Repointing means grinding out failed mortar joints and replacing them. It works when the units themselves are sound and only the joints have gone. When the brick faces have spalled away, repointing puts good mortar between bad brick and buys very little. At that point the honest answer is a rebuild of the section above the roofline, and we would rather tell you that than take payment for tuckpointing that will not hold.