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Hesselberg Hydro

Dungonnell Dam, Ballymena, Northern Ireland

Inspection & maintenance contract for asphaltic concrete lining

Dungonnell Dam is part of a water supply reservoir situated in the Antrim Hills in Northern Ireland and is owned and operated by the Water Services Department. It was completed in the 1970’s and had minimal maintenance since construction.

In 2004 Hesselberg Hydro were invited to inspect the dam. The inspection revealed that there were minor surface defects and that the majority of the mastic seal coat was missing. A contract was awarded to Hesselberg Hydro to repair the defects and replace the mastic seal coat. The slope length was only 8m with a crest wall at the top so mechanical spreading was not feasible. Mastic was placed from a skip and spread manually over the surface.



  • Dam length 250m, maximum height 25m
  • Upstream slope of 1 in 1.7
  • Double layer of asphaltic concrete – 2 x 60mm placed on Binder layer
  • Area requiring new seal coat – 2,000 m2