Stone Consolidating Materials
A Status Report

Abstract

Information on types of stone consolidating materials, their performances, and uses are critically reviewed. Processes responsible for the deterioration of stone and criteria for selecting stone consolidants are also reviewed. The main function of stone consolidants is to reestablish the cohesion between particles of deteriorated stone. In addition, a good consolidant should meet performance requirements concerning durability, depth of penetration, effect on stone porosity, effect on moisture transfer, compatibility with stone, and effect on appearance.

Stone consolidants can be divided into four main groups, according to their chemistry. These groups are inorganic materials, alkoxysilanes, synthetic organic polymers, and waxes. Epoxies, acrylics, and alkoxysilanes are currently the most commonly used consolidating materials. Certain waxes have been found to have excellent consolidating abilities. Waxes, however, tend to soften and to accumulate grime and dust. Inorganic materials and some organic polymers have a tendency to form shallow, brittle layers near the surfaces of stone. These treated layers often separate from the untreated stone. Alkoxysilanes have excellent penetrabilities and are considered by some stone conservators as the most promising consolidating materials. However, a universal consolidant does not exist and many factors must be considered in selecting a consolidant for a specific stone structure.

Key Words: Conservation; consolidating materials; deterioration of stone; preservation; stone; stone consolidation.

Contents

ABSTRACT
1. INTRODUCTION
2. DETERIORATION OF BUILDING STONE
2.1 Salt Crystallization
2.2 Aqueous Dissolution
2.3 Frost Damage
2.4 Microbiological Growth
2.5 Human Contact
2.6 Original Construction

PERFORMANCE REQUIREMENTS FOR CONSOLIDANTS
3.1 Primary Performance Requirements
3.1.1 Consolidating Value
3.1.2 Durability of Consolidated Stone
3.1.3 Depth of Penetration
3.1.4 Stone Porosity
3.1.5 Moisture Transfer
3.1.6 Compatibility of Consolidant with Stone
3.1.7 Effect on Appearance

3.2 Secondary Performance Requirements

STONE CONSOLIDANTS

4.1 Inorganic Materials
4.1.1 Siliceous Consolidants
4.1.1.1 Alkali Silicates
4.1.1.2 Silicofluorides
4.1.2 Alkaline Earth Hydroxides
4.1.2.1 Calcium Hydroxide - -
4.1.2.2 Strontium and Barium Hydroxide
4 1.3 Other Inorganic Consolidants
4.2 Alkoxysilanes
4.2.1 Uses and Developments
4.2.2 Alkoxysilane Chemistry
4.2.3 Performance of Alkoxysilanes

4.3 Synthetic Organic Polymer Systems
4.3.1 Acrylic Polymers
4.3.2 Acrylic Copolymers
4.3.3 Vinyl Polymers
4.3.4 Epoxies
4.3.5 Other Synthetic Organic polymers

4.4 Waxes

5. COMMENTS ON STONE CONSOLIDANTS
6. SUMMARY AND CONCLUSIONS
7. ACKNOWLEDGMENTS
8. REFERENCES
Notes on Electronic Version

7. ACKNOWLEDGMENTS

The author wishes to acknowledge the assistance of Mr. Henry Judd and Mr. Hugh Miller of the National Park Service, who provided information valuable to this review.

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary
  Luther H. Hodges, Jr., Deputy Secretary
  Jordan J. Baruch, Assistant Secretary for Productivity, Technology,
      and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued May 1980

            National Bureau of Standards Technical Note 1118
     Nat. Bur. Stand. (U.S.), Tech. Note 1118, 52 pages (May 1980)
                             CODEN: NBTNAE

                    U.S. GOVERNMENT PRINTING OFFICE
                            WASHINGTON: 1980

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