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The diversity of available stone throughout
Scotland has provided us with a rich
architectural heritage. However it is this very
variety which leads to the difficulty in
attempting to generalise on the causes and
repair of stonework defects. Apart from the most
common problem of the misuse of modern cement
based mortars in rendering or repointing work,
owners may also be faced with spalling and/or
erosion of the stone face. In my own experience,
the deterioration is seldom of structural
concern and the use of indenting new stonework,
“to match” can therefore normally be seen as an
expensive aesthetic repair. Over the past 10
years or so, it is interesting to note that
indented stones may still be unduly prominent on
the elevation and have not “weathered in” as
perhaps promised by the supplier.
Much will therefore depend upon the owner’s view
of what is aesthetically acceptable, although
particularly in urban situations, loose material
may have to be dealt with as a possible hazard
to the public. Should the building be listed,
the appropriate planning procedures should be
followed. Micro climates around the
Surface delamination of ashlar stonework with
previous attempt to repair with cement based
mortar, now failing. |
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property may result in varying degrees of the
visible defect under consideration. The stone
surface itself may have been affected by the
inappropriate of cement based repointing
material in the past. property is large or the
extent of spalling/erosion particular concern, a
geologist may be able to useful background
information, prior to making decision.
Ultimately, consideration might eventually be
given to cautiously cutting back to a sound or
alternatively, applying a lime based mortar
face, following an analysis of the stonework and
the selection of an appropriate specification.
In many cases, the original stonework would been
harled and the “fashion” of exposing underlying
stonework and repointing in cement based
material may have resulted in problems. In this
case, consideration may be given to restoring
the original protective coat of harl.
If the stone has been “cleaned” in the past,
this also have resulted in unnecessary
deterioration.
Thus, it is important to carefully analyse and
consider visible stone defects prior to
specifying an appropriate repair method.
Bill McConnell FRICS
Director
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