Conservation of Historic Stone Buildings and Monuments (1982) / Chapter Skim
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The Evaluation of Stone Preservatives
The Evaluation of Stone Preservatives
Pages 329-340
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From page 329... ...
It concludes by outlining a policy for the use of stone preservatives. The relentless deterioration of ancient monuments and historic buildings is a matter of pressing concern throughout the world.
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From page 330... ...
Historic buildings and monuments are constructed from a bewildering variety of materials and are exposed to a comparable variety of environmental conditions. Preservative treatments accordingly must take many forms to counteract a wide range of decay mechanisms.
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From page 331... ...
The argument is reminiscent of the saying "I've never tried it, because I don't like it," except that here it is put in the converse: "Because I like it, I don't need to test it." EVALUATION BY NATURAL WEATHERING The evaluation of preservatives by exposing treated specimens to the weather is an obvious procedure. IS the long tea it is also the best, for no other procedure can carry 100 percent assurance of demonstrating the performance of preservatives finder natural weathering.
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From page 332... ...
It will be based, for example, on appraisals of surface hardness made by running the finger across the two panels and comparing the amounts of loose stone that it removes the test is reasonably satisfactory at first but meaningless once all the loose stone has been removed from the control panel. Despite the undeniable benefits of evaluation by natural exposure, there is a further drawback.
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From page 333... ...
As a case in point, porosimetry techniques frequently require knowledge of the contact angle between stone and invading fluid. Unless due allowance is made for the change in contact angle upon treatment, direct comparison of results is meaningless..The interpretation of results is further complicated if, as is often the case, the contact angle for the untreated stone lies on one side of 90° and the angle with the treated stone lies on the other.
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From page 334... ...
In the majority, it will not. TESTS SPECIFICALLY POR TREATED STONE Tests intended specifically for treated stone may be grouped into three categories: those aimed simply at characterizing the extent and nature of the treatment, those using accelerated aging chambers, and those aimed at assessing the extent to which treatments meet stated objectives.
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From page 335... ...
Another property frequently required in a preservative is the ability to protect limestone from attack by acidic air pollutants. The capability of a preservative in this respect may be determined, for example, by exposing treated specimens to moist air containing sulfur dioxide.
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From page 336... ...
PERFORMANCE CRITERIA The approach of the preceding section may be given a further degree of sophistication by establishing performance criteria for stone preservatives. Although the concept of performance specification has received considerable attention from the construction industry in recent years, its application to stone preservation appears to have been limited to studies by Gauri and by Sleater Isee Bibliography under Performance Criterial.
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From page 337... ...
They have an air of arbitrariness, which is inevitable in view of the newness of the approach, but further usage should lend weight to the limits prescribed or else provide evidence to support amended values. It would be tempting to assume that compliance with a comprehensive set of performance criteria would provide complete assurance that a treatment was effective and risk-free.
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From page 338... ...
Second, the use of stone preservatives may not be necessary if the stonework is easily accessible to a skilled work force. In such cases it may be preferable to maintain the stonework in sound condition by using adhesives or dowels to secure pieces in danger of falling away, by filling cracks with suitable mortar, by securing loose flakes with a judicious packing of mortar, and by fining water traps.
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From page 339... ...
Studies in Conservation 21:179 {1976J. Tests Primarily for Untreated Stone Arnold, L., and C.A.
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From page 340... ...
Sleater, G.A. Stone preservatives: Methods of laboratory testing and preliminary performance criteria.
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