dk nkf - Nordisk Konservatorforbund Danmark

Prior to the St Just Coast Project’s inception in
1995, however, the utilisation of this material for
conserving the County’s industrial buildings was
not widespread, as most contractors and engineers
felt that it was a weak substitute for cement mortars,
which hardened quickly and were judged to be the
strongest solution for consolidating engine houses.
This seems surprising, as the flexibility and strength
of lime mixes had ensured the long-term survival of
many historic structures, in spite of years of neglect
and unprotected exposure to the elements. Despite
the near abandonment of lime mortars elsewhere,
the Trust developed the use of lime throughout the
decade-long Project. The earliest attempts were
largely determined by the desire to replicate the
colour and texture of the original mixes as they
appeared after years of weathering, rather than their
actual make-up. As a result, dark sands from nearby
Gwithian Beach, rab (orange granitic subsoil) and
mine-waste were added to the lime, as was a degree
of Portland cement. Over time, however, it became
apparent that this method was imperfect, due to the
inflexibility of the cement, and the high clay content
of the rab and sand, which greatly negated the
lime’s chemical effectiveness. This resulted in the
development and constant refinement of lime mortar
mixes and their application, and led ultimately to
the employment of a lime-pointing specialist for the
Project’s final phase.
Working in conjunction with the structural
contractors, this specialist consultant developed
a much more authentic and efficient mix, which
utilised a significantly higher lime content, and
abandoned the use of clay-rich inclusions and
cement. This mixture, which was partly based on
the analysis of original pointing from structures
at Botallack and Kenidjack, was much stronger
physically than previous attempts. It was, however,
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