Caps, Covers and Waterproofing for Magna Chimneys

Exposure changes the specification

There is not much between here and the Oquirrhs, and not much between here and the lake plain. Chimney tops in Magna take wind with real force behind it and very little to slow it down first. Caps that are simply set over a flue tile and held by friction do come off in this city, and the ones that do not come off often work loose and start rattling. What we fit is a cap fastened to the tile or to the crown with mechanical fixings, in stainless rather than galvanized steel, because galvanized rusts through and streaks the masonry within a few years of this kind of weather.

Wind-driven rain and snow

Utah does not get much precipitation, which persuades people that water is not the enemy. On an exposed site, wind delivers what does fall directly into an open flue and hard against the windward face of the stack. Snow driven into a flue melts against warm tile and soaks the masonry from the inside. That is the mechanism behind most of the crown and joint failures we repair here.

Dust is the local extra

Fine windborne dust cakes on cap screens over dry summers and mats them enough to restrict a flue. A cap with generous screen area, and a habit of checking it annually rather than assuming it is fine, matters more in Magna than it does in a leafy part of the valley.

The steel lids on subdivision chimneys

Framed and sided chimney chases have a flat metal cover on top instead of a masonry crown. Builder-grade covers are galvanized, flatten out over time, hold standing water in the middle, and rust through from that low spot. Everything under them is hidden framing, so the leak runs for years before anything shows in the room. A stainless replacement with a proper cross-break for drainage and a sealed collar around the pipe ends it permanently.

Waterproofing and dampers

Sound brick that is porous benefits from a vapor-permeable siloxane repellent, applied after any repointing, never instead of it. Film-forming sealers trap moisture and make spalling worse, so we do not use them. And on an exposed chimney with a leaking throat damper, a top-sealing damper at the crown does two jobs at once: it caps the flue and it actually closes, which the original iron plate has probably not done for a decade.