Waterproofing compound for a concrete roof?

Liquid-applied waterproofing can seal a chimney junction externally at roof level. Leaking chimney junctions are among the most frequent causes of damp damage to a roof. The junction between chimney masonry and the roof covering remains subject to movement from wind loads, temperature changes and settlement; an elastic, crack-bridging rubber membrane permanently accommodates these movements.

The waterproofing adheres to typical chimney substrates, including brick, concrete, sheet metal and fibre cement. The substrate must be clean, dry and sound. At the junction between the chimney and roof surface, a reinforcing fabric is embedded in the waterproofing to strengthen this heavily stressed detail. The waterproofing is taken sufficiently far up the chimney and connected to the roof waterproofing.

This waterproofing can withstand surface temperatures of up to about 100 °C. With typical heating appliances, the outer chimney surface normally remains well below this temperature, particularly in the upper section of the chimney. Waterproofing at a chimney is therefore generally feasible; the actual surface temperature is decisive, and a chimney sweep can advise where there is any doubt.