Cap Flashing and Coping Repair
Metal cap flashings, typically 24-gauge or 26-gauge steel, aluminum, or copper on older buildings, are installed in sections with overlap joints sealed with compatible sealant. The sealant joint is the failure point. UV exposure and thermal cycling compress and stretch sealant at these joints annually, and by year five to seven most sealant at metal coping joints is cracked or debonded.
We do not simply re-caulk failed joints. Re-caulking over deteriorated sealant bonds to old, incompatible material and fails in one to two seasons. Our approach is to remove existing sealant completely, clean the joint surface to bare metal, and apply fresh sealant in the correct bead profile, tooled into the joint, not surface-applied.
Where cap flashing sections have lifted, corroded, or separated from the base flashing below, we replace the damaged sections rather than attempt to re-set lifted metal. Lifted coping is a sign that water has been working behind it long enough to compromise the base flashing, and the base flashing condition needs to be inspected before the cap is reset.
Counter-Flashing and Membrane Termination
The membrane termination at the parapet face is a reglet, a horizontal slot cut or formed into the masonry or metal parapet face, into which a counter-flashing is inserted and sealed. The membrane's base flashing runs up the interior parapet face and laps behind the counter-flashing. This detail is the structural backbone of the parapet waterproofing system.
Counter-flashings fail when the reglet sealant deteriorates, when masonry around the reglet cracks and the reglet opens, or when the counter-flashing itself corrodes or deforms. When counter-flashings fail, water bypasses the membrane termination and enters the wall cavity below, causing interior damage that looks like a roof leak but is actually a wall leak.
We repair or replace counter-flashings to the membrane manufacturer's published detail. On buildings where the original detail does not match current manufacturer specifications, common on older St Louis commercial buildings with mixed repair histories, we bring the detail into compliance as part of the repair.
Masonry Parapet Repointing
Brick and concrete masonry parapets on older commercial buildings, particularly the pre-1970 stock in Downtown St Louis, Midtown, the University City Loop corridor, and the Clayton CBD, develop mortar joint failure over time. Mortar joints in a freeze-thaw environment absorb water, freeze, expand, and eventually crack and spall. Once mortar is compromised, water migrates into the wall cavity whether or not the cap flashing is intact.
Repointing requires removing deteriorated mortar to a depth of three-quarters of an inch to one inch before applying fresh mortar. The mortar mix must match the hardness of the original masonry, using Portland cement mortar that is harder than the brick causes the brick face to spall rather than the joint to erode, which is a worse outcome. We specify mortar mix based on the age and type of masonry on the building.
Parapet repointing is coordinated with cap flashing repair so the sequence is correct: masonry work first, flashing work second, final sealant application last.
Through-Wall Flashing and Scupper Repair
Many older St Louis commercial buildings drain through scupper openings in the parapet face rather than through interior drains. Scuppers require through-wall flashing, a metal sleeve that carries water from the roof deck through the wall and out the face, and the junction between the sleeve and the surrounding masonry is a failure-prone detail. The membrane's base flashing must also be properly lapped onto the scupper sleeve in a watertight configuration.
Through-wall flashing deteriorates from corrosion, masonry settlement, and freeze-thaw movement. Failed through-wall flashing allows water to enter the wall cavity behind the parapet face rather than discharging through the scupper. We replace through-wall flashing and re-coordinate the membrane base flashing termination as a single scope.
Brick Parapet Repair and Tuckpointing in St. Louis's Historic Building Stock
St. Louis has one of the largest concentrations of historic brick commercial buildings of any city in the Midwest. The brick parapets on commercial buildings throughout the City of St. Louis proper, in the historic districts of the inner suburbs, and along the original commercial corridors require masonry repair that is coordinated with roofing flashing work. Missouri's freeze-thaw cycling is particularly aggressive on brick mortar joints: water that penetrates the mortar freezes and expands, progressively spalling the mortar until joints are open and cap flashing below them cannot maintain a watertight seal.
We coordinate parapet masonry repair with roofing flashing work on St. Louis brick commercial buildings, sequencing the tuckpointing and masonry restoration before new cap flashing and base flashing installation to ensure the repaired masonry is the substrate the new flashing bonds to. Applying new flashing over deteriorated mortar joints that will continue to spall produces a flashing failure within one to two Missouri freeze-thaw seasons.
