Abstract

North Foreland Lighthouse is a grade II listed building located 1.2 miles north of Broadstairs in Kent and marks the southerly entrance to the River Thames. The original structure, dating back to 1691, consisted of a twelve metre high octagonal tower constructed from brick quoins and flint panels. Due to navigational requirements and technological developments, the lighthouse has undergone a number of structural alterations throughout its history – a further two storeys were added in 1793; two adjoining keepers’ cottages were built in 1890; internal arrangements have been changed; and windows relocated. The first application of an exterior render was in 1866, and it is believed that the lighthouse was re-rendered in the early 1980s using a cementitious material.

The lighthouse, which came under the ownership of Trinity House in 1832, currently stands twenty six metres high, casting a light nineteen nautical miles out to sea. It remained manned until its conversion to automatic operation in 1998.

Like many lighthouses and coastal buildings, North Foreland is exposed to the harsh conditions of a coastal environment and subject to extremes of weather. It is under constant attack from soluble salts, a principal agent of decay in porous building materials, either precipitated directly, or borne on wind, rainwater or sea spray.

Inappropriate remedial repairs to the lighthouse during the 1980s have led to extensive vertical cracking in the cement-based exterior render, resulting in the ingress, and subsequent trapping, of moisture (and soluble salt) in the mass masonry walls. It is believed that this source of moisture has impacted on the internal environmental conditions within the tower, driving salt-induced decay of interior surfaces. In an attempt to reduce the amount of entrapped moisture within the mass masonry walls, a humidity-regulating vent system – the Schrijver Systeem – was installed at the lighthouse in March 2009.

Since October 2009, a programme of research has been underway, in collaboration with Trinity House, to characterise internal environmental changes within the lighthouse. In the first instance, the aim is to determine the optimal environmental conditions needed to stabilise the observed fabric decay. Ultimately, it is hoped to use the results of the research to develop a model of the interactions between building fabric, moisture content and environmental conditions in order to predict, and hence prevent, fabric deterioration in other historic lighthouses.