Conservation of Historic Stone Buildings and Monuments (1982) / Chapter Skim
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Cleaning and Surface Repair
Cleaning and Surface Repair
Pages 272-280
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From page 272... ...
The work currently being carried out in conservation laboratories is providing essential knowledge both on the behavior of building and decorative stones and on the potential and limitations of various techniques of maintenance. Much of this work relates, properly, to the cleaning and conservation of stone surfaces that have high intrinsic value, and the major practical benefit may therefore be to the conJohn Ashurst is Research Architect at the Directorate of Ancient Monuments and Historic Buildings, Department of Environment, United Kingdom.
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From page 273... ...
Such cleaning systems need upgrading by relevant and sensible specification, rather than by outlawing, which only serves to alienate site practice from good recommendations altogether. In this way, techniques of cleaning, such as clay poulticing, solvent packs and creams, ultrasonic descaling, precision blasting, and consolidation techniques using polyester and acrylic mortars and different silane systems, may be seen as compatible with the proper care of, for instance, a medieval table tomb, while washing, abrasive water jetting, controlled grit blasting, or mild caustic or acid solvent systems will not necessarily be ruled out as suitable means of removing the dirt from nineteenth-century cottages.
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From page 274... ...
Today steam is useful as a support method where greasy deposits are encountered on stone surfaces or sticky substances need to be removed. AIR ABRASIVE TECHNIQUES ("SAND/GRIT BLASTING", Air-abrasive methods probably have caused more damage to masonry surfaces in the past two decades than any others.
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From page 275... ...
They may also be used on heavily soiled limestone, but should not be used on brick or terra-cotta. The work should be finished by rinsing the building face with clean water, preferably using a lowpressure water lance with a fan jet to remove adherent dust.
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From page 276... ...
POULTICE TECHNIQUES In some instances poultice packs, familiar in the monument conservation world, may be used simply and economically by the cleaning contractor. There is no reason, for instance, why magnesium silicate clay packs should not be applied to areas of detail to assist in softening encrustation.
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From page 277... ...
Lime-based treatments, although lately associated with the conservation of external limestone sculpture and carved architectural detail, may be usefully applied to more modest limestone facades that are suffering from the effects of atmospheric pollution. The simplest treatments, but the ones that most substantially change the appearance of a surface, are the traditional tallow-based lime wash, a lime wash based on hydraulic lime, or lime and pozzolanic cenospheres.
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From page 278... ...
The results support the generally, though not exclusively, held view that this class of materials is the most promising of all the surface treatments, with a genuine claim to be described as a "preservative." SURFACE REPAIR The most common surface repair is the refilling of weathered-out joints. In the past this pointing operation has often been earned out by using unsuitable materials with strong hydraulic cement binders, frequently flush-filling over weathered and rounded arrises, thereby
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From page 279... ...
Low sulfate cements, limes, and fly ash are increasingly used, along with various additives, and are better in this respect, but the flushing operation is stfl} a problem and cannot be dispensed with. Massive masonry walls con, however, often be consolidated satisfactorily by gravity or Tow-pressure grouting in small sections.
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From page 280... ...
BIBLIO GRAPHY [Prepared at the committee's request by Anne Grimmer, National Park Service.]
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