What is an upstand in waterproofing?

An upstand is the vertical section where a roof, deck or floor slab turns up against a wall, kerb, parapet or plinth, and where the waterproofing must continue up that vertical face rather than stopping at the horizontal surface. A concrete upstand may be cast as part of the slab or formed separately; either way it exists so that water reaching the edge of the waterproofed area meets a raised barrier instead of a termination. The general rule in UK practice is a minimum of 150mm above finished level, and where the deck can pond, where snow can drift, or where the detail sits below ground and takes hydrostatic pressure, more is required. Terminating a membrane flat at the slab edge with no upstand is one of the most reliable ways to build in a leak. The junction between the horizontal and vertical planes is the vulnerable point. A sharp internal angle forces the membrane or coating round a 90-degree corner, where it thins, bridges, or tears under thermal movement. The remedy is a fillet seal — a cove of epoxy or cementitious mortar, or a preformed fillet, run along the internal angle to turn the sharp corner into a curve of roughly 25-50mm radius. The waterproofing is then dressed over the fillet in a continuous sweep with no stress concentration. Liquid-applied systems normally get reinforcing tape or scrim bedded into the coating across the fillet as well. Common upstand failures are a membrane taken up too low, a termination left unsealed at the top edge instead of being tucked into a chase or held with a proprietary bar, a missing fillet at the angle, and coatings applied at the wrong thickness on the vertical where the material slumps before it cures. MPS Concrete Solutions details and repairs upstands on car park decks, podiums, plant rooms and basements, including fillet seals, reinforced angle detailing and liquid waterproofing to the vertical face.