Quick answers
How are concrete roof drainage channels and basins waterproofed so they don't leak?
Drainage channels and concrete basins carry the heaviest water flow. They are cleaned down to sound concrete and coated in multiple waterproof layers across the floor, the side walls and right into the drain outlet.
Many flat roofs channel all their rainwater into a narrow perimeter gutter or concrete basins leading to the downpipes. Because all the roof's water collects and often stands in those channels, even a small crack in the bottom or corners causes a heavy leak directly below.
On this roof, the drainage channel running along the railings was cleaned and given a grey waterproof base coat followed by a white top coat, carried right inside the drain outlet and up the low parapet walls and railing bases.
The same approach applies to concrete basins and pipe channels: after priming and a grey first coat across the floor and walls, white waterproof coats seal every corner and pipe penetration.
Jobs that show it
Waterproofing a Roof Channel and Upstands
A waterproofing layer, finished with a white coating, went into the channel that collects the water, around the outlets and over the low walls of the roof.
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Waterproofing Inspection Pits and a Channel
Concrete inspection pits with pipe connections and a narrow channel were given coats of waterproofing, first grey and then white, so water can't leak out through their walls.
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Sealing Pipes, Posts and Parapets on a Roof
The places where pipes and steel posts pass through the membrane are usually where water gets in. Here each one was sealed with a white waterproof coating.
See the job step by step