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CO NBS TECHNICAL NOTE 941

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Stone Preservatives:

Methods of Laboratory Testing and

Preliminary Performance Criteria

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NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and

technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to pro- mote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Institute for Computer Sciences and Technology, the Office for Information Programs, and the

Office of Experimental Technology Incentives Program.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consist- ent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry,

and commerce. The Institute consists of the Office of Measurement Services, and the following center and divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center for Radiation Research — Laboratory Astrophysics 2 — Cryogenics 2 — Electromagnetics 2 — Time and Frequency 8

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measure- ment, standards, and data on the properties of well-characterized materials needed by industry, commerce, educational insti- tutions, and Government; provides advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials, the Office of Air and Water Measurement, and the following divisions:

Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services developing and promoting the use of avail- able technology; cooperates with public and private organizations in developing technological standards, codes, and test methods; and provides technical advice services, and information to Government agencies and the public. The Institute consists of

the following divisions and centers: Standards Application and Analysis — Electronic Technology — Center for Consumer Product Technology: Product Systems Analysis; Product Engineering — Center for Building Technology: Structures, Materials, and Safety; Building

Environment; Technical Evaluation and Application — Center for Fire Research: Fire Science; Fire Safety Engineering.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus wthin the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer

languages. The Institute consist of the following divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE OF EXPERIMENTAL TECHNOLOGY INCENTIVES PROGRAM seeks to affect public policy and process

to facilitate technological change in the private sector by examining and experimenting with Government policies and practices in order to identify and remove Government-related barriers and to correct inherent market imperfections that impede

the innovation process. THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and accessibility of scientific information generated within NBS; promotes the development of 'the National Standard Reference Data System and a system of in- formation analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services

to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following organizational units:

Office of Standard Reference Data — Office of Information Activities — Office of Technical Publications — Library —

Office of International Standards — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Located at Boulder, Colorado 80302.
Stone Preservatives:

Methods of Laboratory Testing and

Preliminary Performance Criteria

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Gerald A. Sleater

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

Prepared for:

National Park Service U.S. Department of the Interior Washington, D.C. 20240 ^°' °°< £

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U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

^ C NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued Mav 1977
National Bureau of Standards Technical Note 941

Nat. Bur. Stand. (U.S.), Tech. Note 941, 79 pages (May 1977) CODEN NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1977

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $2.30

Stock No. 003-003-01727-2 (Add 25 percent additional for other than U.S. mailing).
TABLE OF CONTENTS

Page

ABSTRACT 1 INTRODUCTION 2 1.1 Stone Decay and Stone Preservation 2

1 .

Program Ob j ective 3 DEVELOPMENT OF THE TESTING PROGRAM FOR STONE PRESERVATIVES 4

2 .Identification of Causes of Stone Decay 4 2.2 Laboratory Test Procedures: Simulation of Stone Decay and Evaluation of

Test Results 5

2 . 3 Stone Substrate for Test Specimens 6

2 . 4 Stone Preservative Materials 6 2.4.1 Application of Stone Preservative Material 7 EXPOSURE TO COMBINED WEATHERING FACTORS 7

3 .

Chamber for Accelerated Decay (CAD) 8 3.2 Evaluation of Specimens after Exposure in the CAD 8 3.2.1 Weight Changes 10

3.2.2 Change in Appearance 10

3.2.3 Water Absorption 11 3.2.4 Water Vapor Permeability 11

3.2.5 Abrasion Resistance 13

3.2.6 Surface Hardness 13

3 . 3 Summary of CAD Testing 14 INDIVIDUAL TESTS 15

4 .Sulfurous Acid Fog 15 4.2 Salt Action 16 4.2.1 Sodium Sulfate Crystallization 17 4.2.2 Sodium Sulfate Penetration 17 4.2.3 Salt Spray Test 18

4.3 Water Condensation/Evaporation..... 19 4.4 The Effect of Ultraviolet Radiation Upon Stone Preservatives 20

4.5 Suggested Performance Limits from Simulated Tests of Individual Causes

of Stone Decay 21

PRELIMINARY PERFORMANCE CRITERIA FOR STONE PRESERVATIVES 21

5. General Requirements for Stone Preservative Treatments 22 5.1.1 Chemical Compatibility of the Stone Preservative with the Stone... 22 5.1.2 Application of Stone Preservatives 23

5.1.3 Absorption of the Stone Preservative by Stone 24 5.1.4 Environmental Durability of Stone Preservative 25

5.2 The Stability of Stone Preservatives Exposed to Specific Degradation

Factors 25
TABLE OF CONTENTS (continued)

Page

5.2.1 Stability of Stone Preservative Treatments to Air-Borne Chemicals.. 25

5.2.2 Stability of Stone Preservative Treatments to Salt Action 26

5.2.3 Stability of Stone Preservative Treatment to Water Condensation/

Evaporation 26 5.2.4 Stability of Stone Preservative Treatments to Solar Radiation 27 5.3 The Stability of Preservative Treated Stone to Combinations of

Degradative Factors 27

6 . SUMMARY AND CONCLUSIONS 28

7

.

ACKNOWLEDGEMENTS 30

8 BIBLIOGRAPHY 31

APPENDIX A - CONFORMANCE OF STONE PRESERVATIVES TESTED TO CRITERIA 34

TABLES 1 through 13 35 FIGURES 1 through 24 55

Cover Photo: Pueblo Bonito, Chaco Canyon National Monument, New Mexico.
Stone Preservatives: Methods of Laboratory Testing and

Preliminary Performance Criteria

Gerald A. Sleater

Although numerous materials have been proposed as preservatives for

stone in historic buildings and monuments, their efficacy is difficult to establish. In the work described here, a laboratory research program of

accelerated simulated stone decay was used to obtain data on stone preservatives and to suggest criteria for their selection. Over 50 materials

usable as stone preservatives were tested.

Tests to simulate stone decay were of two types:

1. exposure to combined weathering factors using a special test

chamber for accelerated decay (CAD) , in which chemical attack, salt

and water action, and thermal effects were simulated in one operation;

2. exposure to single causes of stone decay using sulfurous acid

fog, sodium chloride fog, water condensation/evaporation cycling,

sodium sulfate penetration and crystallization, and ultraviolet

radiation.

Methods for measuring the effects of the exposures are given together

with the test data; these have been used to set limits of acceptable performance in preliminary performance criteria for the selection of stone

preservatives. The behavior of each stone preservative tested in meeting

these criteria is given. No one stone preservative met all criteria.

Key words: Accelerated laboratory testing; performance criteria; stone

decay; stone preservatives.
1. INTRODUCTION

1. 1 Stone Decay and Stone Preservation

Stone decay, the deterioration of stone from natural weathering or man-made environments

is of increasing concern in the preservation of historic buildings and monuments throughout

the world [1]- Although natural weathering processes will lead to the mineralogical re- adjustment of quarried stone to an atmospheric environment, the change is normally a slow

process [2]. Whereas the increasing incidence of stone decay is often blamed on the

industrial pollution of the 20th century [3] , stone decay may occur where there is no pollution, and not occur where there is serious pollution [4] . One aspect of the problem

of stone decay is, therefore, to determine the causes relevant to each specific case of

decay and to measure and define the effects of this cause. International committees have

been organized to carry out this latter task [5].

International committees are also active in a second aspect of the problem of stone

decay - how to preserve stone [6, 7, 8]. One widely reported means of preserving stone

has been through the use of stone preservatives [9] . Generally, stone preservatives are liquids, which when applied to the surface of the stone impart to the stone properties

that will prevent or retard the decay. Stone preservatives have a long history of use

[10], but information concerning the long-term effectiveness of these reported applications

is lacking. Also, materials that have only recently been used as stone preservatives have

not had time to prove their worth through long-term usage. Because of this lack of longterm performance data for stone preservatives, there should be discretion in their use.

The largest custodian of historic sites in the United States is the National Park

Service, with over 300 national parks and monuments to administer. The use of stone

preservatives in dealing with stone decay problems at historic sites in these parks and

monuments is complicated by factors such as the different types of stone involved and

their usage and condition, the diversity of climates and environments throughout the

national park system, and the need to retain cultural or historic character of the site.

It cannot be assumed that a stone preservative effective at one site will prove equally effective at another site where there is a different environment, type of stone, or degree

of stone decay . For these reasons, the National Park Service has been reluctant to use stone preservatives without a solid base from which to judge their effectiveness.
To obtain such a base of knowledge, the National Park Service requested the National

Bureau of Standards to investigate stone preservatives and develop methods that could be

used to select stone preservatives for field use.

1. 2 Program Objective

One way of meeting the needs of the National Park Service for stone preservatives

would be through the development of performance criteria for their selection. Performance

criteria have been applied in many areas of the building industry [11]; however, their

application to stone preservatives would be new. The advantages of applying performance

criteria to stone preservatives are that they will both describe what the stone preservative

is to accomplish and will define how that accomplishment may be measured. Any material

that meets the appropriate performance criteria can then be tried in the field to find out

if it fulfills the need for a stone preservative at the local site.

For these reasons, the development of preliminary performance criteria for the selection

of stone preservatives became the objective of the research program.

The program was carried out in three phases:

Phase 1 . A literature survey of stone decay, stone testing, stone preservation,

and the use of stone preservatives was done. Information from the survey was

used in developing the testing phase of the program and in writing a state of

the art report on stone preservation [12]

Phase 2 . Practical knowledge of stone decay problems and stone preservation

efforts was gained through on-site inspection of national monuments. The sites

visited included the Lincoln and Jefferson Memorials, and Washington Monument in

Washington, D.C., Federal Hall and Castle Clinton in New York, Chaco Canyon

National Monument in New Mexico, Castillo de San Marcos in Florida, and the El

Moro National Monument in Puerto Rico.

Phase 3 . The major effort in the program was in the development and the application of methods for testing stone preservatives. Information gained through the

first two phases gave a basis for selecting performance requirements for stone

preservatives, and helped identify the tests needed for laboratory evaluation of

preservation performance. The data obtained using the tests became the basis

for the preliminary performance criteria for preservative selection.
2. DEVELOPMENT OF THE TESTING PROGRAM FOR STONE PRESERVATIVES

The laboratory testing program for stone preservatives was developed in five stages:

(1) The identification of the causes of stone decay to be simulated in testing

(Section 2.1)

.

(2) The selection of laboratory procedures to simulate the relevant causes of

stone decay and test methods for evaluating the effects of testing on preservativetreated stone (Section 2.2).

(3) Selection of stone to be used as the substrate material in the testing of

stone preservatives (Section 2.3).

(4) Selection of representative stone preservatives for testing (Section 2.4).

(5) Testing of treated stone (Sections 3 and 4)

.

2 . 1 Identification of Causes of Stone Decay

Stone decay in a structure can be classified as being either intrinsic or extrinsic

in origin [13]. The intrinsic causes come from the nature and the use of the structures.

They include causes, such as structural failures and improper usage of materials, the

effects of which stone preservatives cannot prevent or protect against. Extrinsic causes include the climatic and environmental factors of natural weathering against which stone

preservatives are intended to provide protection.

The following four extrinsic causes of stone decay were chosen for simulation in the

testing program, as they are the most important causes of stone decay [14, 15].

1. Water Action . Water is necessary both for chemical degradation and the

salt action degradation of stone. Water alone can cause stone decay through its

expansion in the pores of the stone upon freezing, or through its dissolution or hydrolysis of mineral constituents of stone [16].
2. Chemical Attack . Chemical attack includes attack by any agent that reacts

chemically with stone. The most important agents are the normal constituents of

the atmosphere and air pollutants [17]. The normal constituents usually react

slowly, as carbon dioxide does with carbonate-containing stone. On the other

hand, air pollutants, such as sulfur dioxide and the oxides of nitrogen - both

forming strong acids with water, are more destructive to stone. These acids

dissolve the stone and form salt deposits that cause further stone decay through

salt action.

3. Salt Action . The destructive action of salts upon building stone occurs in two ways. The first way is from insoluble salt deposits forming hard crusts on the surface of stone. If these deposits spall, they remove the surface of the

stone to which they adhere anc expose a fresh stone surface to weathering [18].

The second way for destructive salt action is through crystallization of salts

in the pores beneath the surface of the stone. As these salt deposits build up, or as the salts crystallize in different forms, forces may develop within the

stone which may eventually cause spalling to occur [19] . Salts may be the

residue of chemical attack on the stone or on other building materials. Salts

may also be transported into the structure by groundwater, or they may be carried

by rain or wind.

4. Thermal Effects . Diurnal temperature variations cause expansion and contraction of stone, and can lead to differential expansion of mineral components or salts in the stone [20]. Below-freezing temperatures are necessary for freeze/

thaw damage to water-saturated stone.

2.2 Laboratory Test Procedures: Simulation of Stone Decay and Evaluation of Test Results

Two approaches were used to simulate these causes of stone decay in laboratory testing:

(1) Combined Testing : Simulating several causes of stone decay in one test operation. This approach is described in Section 3.

(2) Single Tests : Simulating a single cause of stone or stone preservative

decay in one testing procedure. This approach is described in Section 4.
2 .3 Stone Substrate for Test Specimens

Indiana limestone (Standard Gray) was chosen as the substrate for the testing of

stone preservatives. It is widely used as a building stone throughout the United States

[21]. Its properties fitted the needs of the test program: it was susceptible to, but not

rapidly destroyed by acid attack in the CAD (described in Section 3.1); the effects of CAD

testing upon its properties, such as water absorption and hardness, were measurable; stone

preservatives could penetrate into the stone.

Test specimens were cut at NBS from unweathered limestone purchased from a commercial

quarry. After cutting, the specimens were washed several days with running tap water to remove stone dust, then dried at room temperature (22-25°C) under a vacuum of 5-10 mm of

mercury for 8-16 hours. The dry specimens were then used for testing or stone preservative

treatment.

2.4 Stone Preservative Materials

The materials tested for stone preservation treatments were obtained from commercial

suppliers. Although most were primarily intended for treatment of stone, concrete, or masonry to produce water repellency, "waterproofing," or surface hardening, such materials

may also be useful as stone preservatives and they are all described as stone preservatives

in this report. Each stone preservative was given a two digit code number to identify it.

Uncoated limestone specimens were coded 00.

Several materials, such as saturated calcium hydroxide solution (limewater) and

linseed oil, that have long been used as stone preservatives [22] were also included in

the study. They were bought from chemical supply houses.

Table 1 lists some important properties of these materials. The qualitative composition

of a stone preservative was supplied by the manufacturer or determined, when possible,

from its infrared spectrum. Nonvolatile content was the residue obtained by evaporating

to dryness a weighed amount of the material at 105°C. The color of a preservative refers

to its appearance in liquid form. "waterwhite" describes a liquid which has the colorless,

transparent appearance of water. Miscibility and reaction with water were determined by

mixing equal proportions of stone preservative and water; after mixing, the pH of the

water phase was determined with pH- indicating paper (only pH values above pH 7 or below pH

5 are recorded in table 1) . The color and general physical characteristics of the dried

film are those of the film or the deposit obtained by evaporation of the liquid preservative

at room temperature.
The appearance and the surface texture of the Indiana Gray limestone, as determined

by visual observation, and the percent weight increase in the specimens after application

of the preservative treatment (Section 2.4.1) are given in table 2. Figure 1 illustrates

the differences in appearance among preservative-treated specimens of Indiana gray limestone,

The depth of penetration of the stone preservatives into unweathered limestone

(table 2) was determined by sawing the treated specimens in half. How deep the penetration

of a preservative into unweathered limestone could be is illustrated in figure 2.

2.4.1 Application of Stone Preservative Material

Most suppliers of stone preservative materials recommended their application by brush

or spray. In this program, the dry limestone specimens (Section 2.3) were treated only

once, the preservative solution being brushed on all sides of'a specimen (in a laboratory

exhaust hood) until it was no longer absorbed by the stone. After air-drying in the hood,

specimens were further dried at room temperature (22-25°C) under a vacuum of 5-10 mm of

mercury for 8-16 hours.

Vacuum drying was used after most testing procedures to avoid possible damage to the

preservative treatments by drying at oven temperatures (100°C) . An exception were the

sodium sulfate tests (Sections 4.2.2 and 4.2.3) in which a temperature of 105°C was needed

to obtain anhydrous sodium sulfate.

3. EXPOSURE TO COMBINED WEATHERING FACTORS

By combining in one testing operation the major causes of stone decay — water and

salt action, chemical attack, thermal effects — an attempt was made to simulate the

synergistic action of stone decay factors sometimes found in nature, and as in nature,

without being able to assign to each cause its contribution to the decay process.

The combined exposure testing was done using a special test Chamber for Accelerated

Decay (CAD) and test cycle developed by the Illinois Institute of Technology Research

Institute (IITRI)
3.

1

Chamber for Accelerated Decay (CAD)

The CAD, built of stainless steel by IITRI, is illustrated in figure 3. Its features

include: A) three infrared and six ultraviolet lamps; B) a water spray; C) a revolving

eight-sided specimen drum; D) each face of the drum can hold up to 15 test specimens (each

10 cm x 10 cm x 2.5 cm) on removable plates; E) a motor and reduction gearbox for rotation

of the specimen drum; F) an inlet for corrosive test solutions (60 liters of solution will

fill the chamber to the bottom face of the specimen drum) ; G) an outlet through which the

corrosive test solution can be pumped back to storage for reuse; H) a drain that can be

completely closed by a valve when the corrosive test solution is being used, or only

partially closed by a stand pipe during water-soaking of the specimens.

To simplify testing, only one size limestone specimen (10 cm x 10 cm x 2.5 cm) was used in CAD testing. Test specimens of other shapes and sizes (round sections cut from

cores, for instance) could be used in the CAD by changing the mounting fixtures.

The CAD test cycle (table 3) combines chemical attack, salt and water action, and

thermal effects in one operation. Freeze/thaw action was obtained by removing the plates

holding the specimens from the CAD after they had been soaked in the sodium chloride/sulfurous

acid solution and storing them overnight in a deep freezer at -40°C. As many of the stone

preservatives contained organic resins, which might be degraded by solar ultraviolet

radiation [23], ultraviolet lamps were used to simulate this radiation in the CAD.

Table 4 is a matrix showing the contribution of each feature of the CAD to the different

causes of stone decay being simulated.

3.

2

Evaluation of Specimens after Exposure in the CAD

Both preservative treated and untreated stone specimens were exposed in the CAD.

Stone specimens were evaluated after periods of 10 and 20 CAD test cycles. Twenty test cycles were usually sufficient to prove lack of durability of the stone preservatives;

evaluation of specimens after 10 cycles helped to detect the onset of degradation and

trends in specimen behavior. Separate test specimens were used for each CAD test cycle of

a stone preservative. (In some test runs duplicate specimens treated with the same preservative were used to test reproducibility of the evaluation measurements. This reproducibility

was good.) After completion of the chosen number of test cycles, specimens were removed

from the plates on which they had been mounted for CAD testing and were washed for 8-16

hours in running tap water. The specimens were then dried as described in Section 2.3.
The effects of stone decay are shown through surface degradation, internal alterations

(visible, invisible), freezing breakage, and stains [24]. The effectiveness of a stone

preservative is defined by how well it prevents or modifies these conditions. Measurement

of certain surface or bulk properties of stone can be used to determine this effectiveness.

The effectiveness of stone preservatives in modifying the effects of CAD exposures on the limestone substrate was evaluated by measuring changes in six properties of the test specimens:

(1) Weight . The most serious effect of stone decay is the material breakdown

of the stone. The breakdown of the stone and the consequent loss of stone

particles can be measured by the weight changes caused by CAD testing. These

changes are discussed in Section 3.2.1.

(2) Appearance . In natural weathering small changes in the appearance of stone are accepted, even wanted. Grosser changes due to surface grime or salt deposits

can degrade the stone as well as be unsightly [25]. In CAD testing, changes in

appearance were determined both by visual examination and by instrumentally

measuring the changes in color and gloss. The results of these measurements are given in Section 3.2.2.

(3) Water Absorption . The passage of liquid water through stone can be an important factor in stone decay (Section 2.1). How well stone preservatives

prevent the passage of liquid water through stone can be determined by measuring

the water absorption of the treated stone. The water absorption values and

their changes resulting from CAD testing are described in Section 3.2.3.

(4) Water Vapor Permeability . The passage of water vapor through stone and its

evaporation from the surface is one way in which liquid water escapes from

within a stone. If this "breathing" is prevented by stone preservatives or deposits that seal the surface, liquid water trapped within the stone can lead

to enhancement of the problems from water action (Section 2.2). Water vapor

permeability measurements are discussed in Section 3.2.4.

(5) Abrasion Resistance . Resistance to mechanical wear is one indication of

the cohesion of the surface particles of stone; loss of surface particles

("sugaring") is frequently observed in stone degradation. How well a stone

preservative hardens or toughens the surface of the stone to prevent "sugaring"

can be measured by the abrasion resistance of the treated stone. Abrasion

resistance measurements are described in Section 3.2.5.
(6) Surface Hardness . Measurement of the surface hardness (resistance to deformation) is a relative indication of the strengthening of stone by a preservative treatment. Surface hardness is covered in Section 3.2.6.

3.2.1 Weight Changes

After drying (Section 3.2) specimens were weighed to 0.1 milligram. Any change in

specimen weight is expressed as weight percent. Weight changes from CAD testing are listed in table 2.

Loss of weight indicates how much of a test specimen (stone and/or stone preservative)

has been lost through CAD testing. All test specimens lost some weight during CAD testing

except those treated with preservative 51 — these gained weight. Untreated limestone

specimens lost approximately 1% of their initial weight after 10 cycles of CAD testing,

and 2% after 20 cycles. Most treated specimens had less weight loss than the unprotected

limestone specimens, although specimens treated with preservatives 4, 6, 10, 13, 49, and

50 lost slightly more weight.

3.2.2 Change in Appearance*

The effect of CAD testing upon the appearance of the test specimens was measured

using ASTM D 2244-68 (27)**, Test for Instrumental Evaluation of Color Differences of

Opaque Materials; and ASTM D 523-67 (27), Test for Specular Gloss.

The initial effects of the different stone preservatives treatments on Indiana limestone

are shown in figure 1. CAD testing can lead to further changes in specimen appearance,

varying from slight changes (figure 4) to extreme differences in color (figure 5) . Figure

6 shows changes that came about as a preservative treatment was lost — the residue adhering

to the stone being one color, the body of the stone another color. Figure 7 is a close-up

of the specimen in figure 6 after exposure to 20 CAD cycles.

Color values for the tested specimens were calculated from readings made with a three

filter colorimeter (ASTM D 2244-68, Section 3.8.1.2). The color difference (E) between

the tested specimens and untested specimens is given in figure 8 in bar graph form. Gloss

measurements were made for stone preservatives that imparted a gloss to the specimen.

However, all specimen gloss was destroyed during CAD testing, and no measurement of gloss

could be made after CAD testing began.

* Presently of great interest to the appearance of stone is the problem of graffiti. Two

recent NBS publications that cover parts of the graffiti problem are listed in reference 26. ** The numbers in parenthesis following the ASTM Test Methods indicate what volume of ASTM

Test Methods (1975 edition) the test method can be found in. ASTM Standards may be obtained

by applying to the American Society for Testing and Materials, 1916 Race Street, Philadelphia,

Pennsylvania 19103.

10
Although the color difference E is useful for determining whether or not a specimen's

appearance is within specified limits, a visual estimation of color difference is also

recommended. For example, the specimens shown in figure 6 had color changes less than

untreated limestone (7 units) after CAD testing, yet these specimens appear degraded.

Changes in appearance must, therefore, be judged visually, and if possible, determined

instrumentally.

3.2.3 Water Absorption"

The absorption of liquid water by stone specimens was measured by following the procedure of ASTM C 97-47 (19) , Standard Methods of Test for Absorption and Bulk Specific

Gravity of Natural Building Stone.

Water absorption was measured by immersing the test specimens completely in a stirred

distilled water bath for 48 hours at 22-24°C as called for in the ASTM Test Method. The

specimens were then removed from the water and quickly weighed, after wiping off the

surface water on the specimens with a damp cloth. The results of the water absorption

measurements are given in bar graph form in figure 9.

The effects of CAD testing on the water absorption of preservative-treated specimens

can be classified in three categories: 1) little change, for those treated specimens

which had a water absorption before testing approximately that of untreated limestone; 2) a great increase in water absorption after testing - the expected effect as the stone

preservative treatment is lost; 3) fluctuations — the water absorption values increasing

then decreasing, or vice versa — which may be due to blockage of the pores of the stone

by salts or other materials.

The water absorption of untreated Indiana limestone was 6% before and after CAD

testing. Water absorption remained below 6% for 20 CAD cycles for specimens treated with

24 of the 53 stone preservatives.

3.2.4 Water Vapor Permeability

The permeability of the test specimens to water vapor was measured using ASTM Test

Method C 355-64 (18) , Standard Methods of Test for Water Vapor Transmission of Thick

Materials.

* Performance tests specifically for waterproofing materials are given in reference 27,

11
Cups (figure 10) to hold the square test specimens were fabricated from 1 millimeter

thick aluminum sheet. The insides of the cups were protected against corrosion by the

desiccant and made airtight by a coating of paraffin wax. To measure water vapor permeability

calcium chloride desiccant was added to the cups and the test specimens taped to the cups

with adhesive aluminum tape. The cups and attached specimens were kept in a constant

humidity room (50% ± 4% RH and 23 ± 1°C) , and periodically weighed until the rate of water

pickup by the desiccant was constant. The rate of weight increase measured the rate at which water vapor passed through the test specimen.

The Water Vapor Transmission (WVT), Permeance, and Average Water Vapor Permeability

(WVP) of the specimens were calculated from the test data.

WVT = weight change in grams/test area (square meters)

Permeance = WVT/S(R -R )

S = saturation vapor pressure at test temperature

R = relative humidity in constant temperature room

R„ = relative humidity inside cup

Average Permeability* = permeance x specimen thickness (cm)

.

Because specimen thickness varied between 2.30 cm and 2.50 cm, the test results were

expressed as water vapor permeability (WVP) . The WVP values are given in bar graph form

in figure 11.

Water vapor permeability measurements show that both tested and untested specimens

are permeable to water vapor. WVP changes caused by testing are similar to the changes

observed in liquid water absorption (Section 3.3.3), the same preservative treatments

often exhibiting the same trends. The type of variation in WVP during CAD testing were

similar to the variations in water absorption: 1) little change between the tested and

untested specimen WVP values; 2) an increase of WVP with testing; 3) fluctuations. The

water vapor permeability of the untreated limestone decreased 25% during 20 CAD cycles —

from 3.3 metric perm-cm to 2.5 metric perm-cm. Specimens for stone preservative treatments

05, 09, 38, 55 remained at or decreased from this level during CAD testing.

* To convert from permeability in metric perms units to permeability in SI units (International System of Units), the following factors are used:

metric perm-cm (multiplied by 0.598) = perm- in (23°C)

perm-in @ 23°C (multiplied by 1.46 E-12) = kilogram/pascal-second-metre.

12
3.2.5 Abrasion Resistance

The resistance of test specimens to surface abrasion was measured using the equipment

and test procedure described in ASTM D 1044-56 (35) , Test for Resistance of Transparent

Plastics to Surface Abrasion.

The abrasion testing machine (figure 12) was modified to hold the square test specimens

by attaching four adjustable sides to the rotating stage of the machine. In testing for

abrasion resistance the specimen (C) was firmly clamped to the rotating stage by the

adjustable sides (D) ; two separate grinding wheels (B) , each with a test load of 1 kilogram

(A), were placed on the surface of the specimen and the stage rotated. Each rotation

cycle was recorded by a counter. As the specimen rotated beneath them, the weighted

grinding wheels abraded its surface. The weight loss (in milligrams, mg) of the specimen

per rotation was used to measure the resistance of the specimen — and preservative treatment

to abrasion. The results of the abrasion resistance measurements are given in figure 13.

As with other properties of test specimens measured after CAD exposure, abrasion

resistance increased, decreased, or fluctuated with CAD testing. Untreated limestone

specimens increased in abrasion resistance (i.e. a decrease in surface matter abraded)

with CAD testing; this increase may be due to the loss of loose surface granules during

testing, or to the cementing action of residues or chemical reaction on the surface.

Many specimens treated with stone preservatives that did not penetrate deeply into

the stone (see table 2) had an initial high abrasion resistance, but as the surface

coating was lost with testing there was a sudden decrease in protection — this behavior was shown by specimens treated with preservatives 24, 30, 34, 49. Some stone preservatives

that penetrated deeply into the stone (09, 12, 18, 25) retained a relatively high abrasion

resistance throughout CAD testing.

(In this project unweathered stone was used as test substrate. In testing where

weathered stone or stone with a low abrasion resistance is used, the strengthening effect

of stone preservatives on the stone should be much greater and more easily determinable by

abrasion resistance measurements.)

3.2.6 Surface Hardness

Surface hardness was measured using the method and equipment described in ASTM E 18-

67 (10), test for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials.

13
Measurements were made with ROCKWELL-WILSON Hardness Tester*, Model 3-JR. Rockwell

hardness values were read on the C-scale of the Tester dial gauge, using a steel ball

surface penetrator (1.2 cm diameter) and a major test load of 60 kgf. The accuracy of the

dial gauge was checked by measuring the surface hardness of a standard steel block.

In measuring surface hardness, one square face of the specimen was placed on the

anvil of the hardness tester, and the penetrator pressed into the opposite face by a minor

test load of 10 kgf. The pointer of the dial gauge was then set at zero, and the major

load applied. The Rockwell hardness value is the depth of penetration of the penetrator

caused by the major load. The measured Rockwell hardness values are given in bar graph

form in figure 14.

The surfaces of all untreated and some treated limestone specimens did not correspond

to the smooth, polished metal surfaces for which the hardness test is intended. This

surface roughness was roughly compensated for by using a large diameter penetrator. The

surface hardness of specimens for preservative 51 could not be read, because the penetrator

continued to sink into the specimen and did not come to rest under the minor load.

During CAD testing, specimens treated with stone preservatives 09, 21, 35, 45 decreased

in surface hardness 20% or more from the surface hardness of the untested limestone. The

surface hardness of the other preservative treatments showed only slight variation consequent

to testing.

3. 3 Summary of CAD Testing

To summarize the usefulness of CAD testing in regard to studying stone preservatives:

(1) CAD testing caused measurable deterioration of stone untreated with stone

preservatives within the reasonable time of 20 CAD test cycles. This deterioration could be measured through changes in certain properties of the test specimens - such as weight, appearance, water absorption, water vapor permeability, abrasion

resistance, and surface hardness.

(2) CAD testing caused, to varying degrees, changes in the same properties for

preservative-treated stone specimens. The effectiveness of the preservative

treatment on a specimen could be judged by how well it prevented changes in

these properties equivalent to those for untreated stone.

* Description of a specific test instrument is to assist duplication of the testing

procedure; it does not imply endorsement by the National Bureau of Standards.

14
(3) From evaluation of the effects of CAD testing of over 50 stone preservatives,

appropriate upper limits of the property changes expected from the more effective

preservatives can be identified. These limits are used in Section 5 to establish

preliminary performance criteria for selection of stone preservatives for field

testing. (How well the stone preservatives tested in Section 3 meet these

criteria is indicated in table 12.)

INDIVIDUAL TESTS

In circumstances where it is determined that one cause is the major influence in

stone decay, selection of a stone preservative can be based upon simulated testing involving

that cause alone. In this project the causes of stone decay and stone preservative deterioration that were simulated individually were:

Chemical Attack: Sulfurous Acid Fog Test (4.1)

Salt Action: Sodium Sulfate Crystallization Test (4.2.1)

Sodium Sulfate Penetration Test (4.2.2)

Sodium Chloride Fog Test (4.2.3)

Water Action: Water Condensation/Evaporation Test (4.3)

Ultraviolet Radiation Degradation of Preservatives: Ultraviolet Radiation Test

(4.4).

4.1 Sulfurous Acid Fog

The effect of a sulfurous acid environment on stone preservative treatments was evaluated by exposing test specimens to a sulfurous acid fog.

This test used the corrosion test chamber (Kesternich Cabinet) and the test procedure

described in the German Industry Standard DIN 50 018, Testing of Materials, Structural

Components and Equipment; Method of Test in Damp Heat Alternating Atmosphere Containing

Sulfur Dioxide (Cabinet according to Kesternich) [28].

The test cabinet and its accessories are illustrated in figure 15. For each test cycle two liters of distilled water were poured into the test cabinet (A) to cover the

lead-lined bottom. Two liters of sulfur dioxide gas from the gas cylinder (B) , measured

by the container (C) , were passed into the closed cabinet through the gas inlet valve (D)

Only then were the electrical heating elements in the bottom of the cabinet turned on. Within 90 minutes the temperature in the lower part of the cabinet reached 35 °C, resulting

in a fog of sulfurous acid that filled the cabinet and covered the test specimens. After

8 hours the heating was stopped and the cabinet cooled overnight (16 hours) with the door

ajar. The water remaining in the cabinet was drained and replaced with fresh distilled

water before starting a new test cycle.

15
Single test specimens (2 cm x 2 cm x 1 cm) were treated on five sides with each stone

preservative; one large face of each specimen was left untreated in order to observe the

effect of the test on untreated as well as treated stone. The specimens were placed on neoprene mesh midway between the top and bottom of the cabinet; they were not washed or otherwise cleaned between test cycles.

After 49 test cycles (8 hours heating and 16 hours cooling) the specimens were removed

from the cabinet, washed three times with distilled water, and dried under vacuum (Section 2.3)

The changes observed in the tested specimens are given in table 5. Figure 16 illustrates

the changes in appearance consequent to this test. Figure 17 is a close-up of three

specimens. Most specimens were affected to some degree by the sulfurous acid atmosphere.

Although, the surfaces of some specimens had blistered or changed color, the most common change was a visible white surface deposit of small (less than 0.1 mm) acicular crystals,

presumably calcium sulfite or sulfate, too small for analysis. There was no great difference

between the treated and untreated surfaces of specimens affected by testing.

The concentrations of sulfurous acid used in the sulfurous acid fog test or in the CAD

weathering cycle did not physically destroy the limestone substrate material. The effect

of concentrated sulfurous acid flowing over Indiana gray limestone is shown in figure 18; no similar destruction of the stone was observed in either the CAD or Kesternich tests.

The 60 liters of 0.01 molar sulfurous acid solution used in the CAD test had a concen- tration of approximately 800 parts per million (ppm) sulfur dioxide. Two liters of sulfur

dioxide gas added to the Kesternich test cabinet (volume 300 liters) gave a fog with a sulfurous acid concentration of 15,000 ppm sulfur dioxide. Both concentrations are higher than

the pollution levels of sulfur dioxide normally found in urban environments. For example,

between 1954-64 the annual mean concentration of sulfur dioxide in London, Great Britain, was 0.12 ppm [29]. In the fog test the level of sulfur dioxide was over 100,000 times greater,

and in the CAD test over 6,000 times greater.

4.2 Salt Action

Three types of salt action (see Section 2.1) on stone or stone preservatives were

simulated: 1) crystallization of salt within stone (Sodium Sulfate Crystallization, 4.2.1);

2) penetration of salt solution through a preservative treatment (Sodium Sulfate Penetration,

4.2.2); 3) penetration through, or degradation of a preservative treatment by air-borne

salt solution (Salt Spray Test, 4.2.3).

16
4.2.1 Sodium Sulfate Crystallization

The resistance of preservative treated specimens to the effects- of salt crystallization

was evaluated by cyclic sodium sulfate crystallization tests.

Testing followed ASTM C 88-69 0.5) , Standard Method of Test for Soundness of Aggregates

by Use of Sodium Sulfate or Magnesium Sulfate. Test specimens were limestone prisms (10 cm

x 2.5 cm x 2.5 cm); single prisms were treated once on all sides with each stone preservative,

which was brushed on until no more was absorbed by the stone.

Specimens were tested up to 10 cycles. Each test cycle consisted of immersing the

test specimen for 16 to 18 hours in a stirred, saturated sodium sulfate solution kept at 22-24°C, removing the specimens from the solution and drying them at 105 °C for four hours.

The dried specimens were weighed, then re-immersed in the sodium sulfate solution.

During each test cycle, the sodium sulfate solution absorbed by the specimen is dehydated

by heating to 105°C. Upon re-immersion hydrated sodium sulfate is formed within the specimen,

and the greater crystal volume of the hydrated salt exerts pressure on the confining stone. Untreated limestone prisms began to spall after two test cycles.

The cumulative specimen weight changes from cyclic sodium sulfate crystallization are given in table 6. Figure 19 illustrates how specimens increase in weight as sodium sulfate

is absorbed, then begin to deteriorate and lose weight. The degradation of the test specimens

by sodium sulfate crystallization is illustrated in figure 20.

Only specimens treated with 10 stone preservatives showed little or no weight loss

after 10 test cycles; each of these preservatives penetrated 5 millimeters or more into

Indiana limestone (see table 2)

4.2.2 Sodium Sulfate Penetration

The resistance of stone preservative treatments to the penetration of salt solutions

was evaluated through modification of the Federal Specification for Water-Repellent

Colorless, Silicone Resin Base, SS-W-110C [30]. Section 4.3.5 of this Specification tests

the resistance of specimens to efflorescence by immersing an unprotected surface of the

test specimen in 10% sodium sulfate solution for 7 days. The specimen is then removed from

the solution and dried, and any efflorescence on the treated surface opposite to the immersed,

untreated surface noted.

17
To test for penetration of a salt through a stone preservative treatment, and to discover the effect drying or absorbed salts have on stone preservative treatments, the

above procedure was reversed. Single test specimens (5 cm x 2.5 cm x 2.5 cm), treated on five sides for each stone preservative tested, were placed in a 10% sodium sulfate solution

at 22-24°C with the one untreated surface uppermost; the bottom treated surface was just

wetted by the solution. After seven days the specimens were removed from the solution,

dried overnight (16 hours) at 105°C. After the specimens were dried, the untreated surfaces were inspected, and the specimen weighed. Specimens were tested for three cycles of seven

days each.

The condition of the dry test specimens after three test cycles is given in table 7. The top, uncoated surface was degraded either through swelling and loosening of the stone

granules, or by the appearance of dried white salt deposit (efflorescence). Degradation of

the specimen's sides, which were treated with stone preservative, was through spalling of

the treated zone from the body of the specimen. No change in appearance or physical state was found for test specimens of 20 of the 51 stone preservatives tested. There was no correlation between the weight of sodium sulfate absorbed by a test specimen (usually no more than a 1% increase in specimen weight) and degradation of the specimen. The destructive

action of salt penetration on the stone is shown in figure 21.

4.2.3 Salt Spray Test

Stone preservative treated specimens were exposed to a salt (sodium chloride) spray

environment by following the procedure of ASTM B-117-64 (9) , Standard Method of Salt Spray

(Fog) Testing.

Treated specimens were exposed to a sodium chloride atmosphere in order to determine

what effect sodium chloride would have on the preservative treatments, and whether sodium

chloride would be absorbed by the stone.

The test apparatus was a clear plastic chamber (1 m x 1 m x 1.1 m) maintained at 35°C.

Compressed oil-free air, saturated with water vapor, was blown through a 5% sodium chloride

solution in the chamber, resulting in a fine mist, or fog, of sodium chloride solution

filling the chamber and covering the test specimens which were on a neoprene mesh in the

top of the chamber. The test ran continuously for 6 months (180 days).

18
Single limestone test specimens ( 2 cm x 2 cm x 1 cm) were treated on all sides with

each stone preservative. The tes't specimens were periodically inspected, and the presence

of any surface deposits, blistering, or significant changes in the. specimens were noted.

Only two specimens (31, 38) showed visible changes - after 100 hours both had crystalline

substances which gave a basic reaction (pH greater than 11) . These deposits disappeared

with further testing. After 180 days all specimens were removed from the chamber. Weight

changes from salt pick up were insignificant. However, changes in appearance after washing

and drying of the specimens were noticeable (figure 21)

4. 3 Water Condensation/Evaporation

The effects of cyclic water condensation/evaporation on stone preservative-treated

specimens were evaluated by using the test chamber and procedure described in ASTM D 2247-

68 (27), Standard Method of Testing Coated Metal Specimens at 100 Percent Relative Humidity.

The test chamber is shown in figure 23. The test specimens were mounted over a water

bath (B) kept at a temperature of 38°C. After 90 minutes of water condensation on the

specimens, the water was evaporated from the face of the specimens by warm air blown

through (C) . Following 30 minutes of air-drying, water condensation was repeated. The 90

minutes of water condensation and 30 minutes of warm air-drying constituted one testing

cycle.

Stone prisms (5 cm x 2.5 cm x 2.5 cm) were used as test specimens. Five sides of each

prism were treated with stone preservative; the one large rectangular face that was not

treated faced away from the water bath and was exposed to the room atmosphere.

Testing was continued for 5 months — 2400 testing cycles. Water condensation/evaporation was used to simulate the cyclic water condensation/evaporation that is an important

factor in natural weathering [31]. Evaluated in this test were: 1) absorption of water by

the specimen; 2) breakdown of the preservative treatment. These effects were evaluated by

periodically removing the specimens from the water bath, observing their appearance, testing

the pH of the water condensate, and determining any weight increase.

Specimens that did increase in weight are listed in table 8. These specimens were

treated with the same stone preservative treatments that had high water absorption in water

absorption testing (Section 3.2.3),

19
Surface deposits formed on seven specimens during testing (table 9) . These deposits

appeared either on the untreated surface facing away from the bath, or just below the

untreated surface on the side above a wetted zone extending up from the surface which faced

the water bath. The deposit, illustrated in figure 24, probably comes from degradation of

the preservative and transport of the degradation products by water through the specimen.

After 75 hours testing, the condensate on four specimens (10, 18, 31, 38) gave a basic

pH reaction (pH greater than 10) when tested with pH- indicating test paper. The salt

deposits that had appeared on the surfaces of specimens 31 and 38 disappeared with further

testing.

4.4 The Effect of Ultraviolet Radiation Upon Stone Preservatives

The effect of ultraviolet radiation upon stone preservatives was determined by exposing

preservative-treated specimens to ultraviolet radiation in a xenon-arc apparatus.

Method (A) of ASTM G 27-70 (41), Standard Recommended Practice for Operating Xenon-Arc

Type Apparatus for Light Exposure of Nonmetallic Materials, was followed. A Model 60-WR

Atlas Weather-Ometer with a 6000 watt water-cooled xenon-arc lamp and borosilicate inner

and outer glass filters was used. Light exposure was continuous with no water spray on the specimens. Black panel temperature in the test chamber was kept at 62°C.

To better detect color changes in this test, stone preservatives were applied to a white substrate. White unglazed paper and white unglazed tile were both tried as substrates,

but many preservatives were not absorbed by either material, either puddling or beading on their surfaces. A uniform absorption of preservatives was obtained with unpolished, sandrubbed texture white Yule marble, and specimens of this stone (10 cm x 10 cm x 2.5 cm) were

used as substrate.

The treated test specimens were hung with steel straps from the revolving specimen

rack around the xenon-arc lamp. The positions of the specimens on the drum were changed

periodically during testing to give them more uniform exposure to the xenon-arc.

Specimens were exposed to the xenon arc for up to 1100 hours. At periods of 300, 600,

and 1100 hours, the specimens were removed and inspected for the appearance of yellowing.

Only 13 of the 49 stone preservatives tested showed yellowing during the test (see table 10)

.

20
4.5 Suggested Performance Limits from Simulated Tests of Individual Causes of Stone Decay

In evaluating stone preservative performance, simulation of a single cause of stone

decay can be useful when that cause is known or suspected to be involved in stone deterioration. As with CAD testing (Section 3.3), varying degrees of protection were given to the

stone specimens by the preservatives.

By studying the effects of these tests on specimens treated with over 50 stone preservatives, a judgment can be made as what is acceptable stone preservative performance for

each simulated cause of stone decay. These judgments are the basis for the preliminary

performance criteria for stone preservatives given in Section 5. The behavior of the stone

preservatives used in this program in meeting these limits is indicated in table 13.

5. PRELIMINARY PERFORMANCE CRITERIA FOR STONE PRESERVATIVES

Preliminary performance criteria for the selection of stone preservatives have been

developed through knowledge gained in all three phases of the research program. The Phase

I literature survey gave information about research that had been done in stone preservation,

identified causes of stone decay, and indicated the needs in stone preservation work. The

on-site inspections done in Phase II gave practical information about current problems in

stone decay and stone preservation. The Phase III laboratory program showed that simulation

of the environmental factors causing stone decay can be used (1) to distinguish differences

in stone preservative behavior, and (2) to establish preliminary criteria to serve as guides to acceptable performance.

When choosing a stone preservative for a specific stone decay problem it is essential

to identify the cause of decay . Only in this way is it certain that the work undertaken is

appropriate to stopping, or at least modifying, the decay process. The performance criteria

given in this Section require this step to be carried out. The user must therefore decide

which performance requirements for stone preservatives fit his problem of stone decay, and

which criteria should be applied in selecting preservatives .

Because these criteria will undoubtedly be revised as experience and testing give new information about stone preservative performance, they are designated as preliminary

criteria. Until their relationship to field performance is more firmly established, it is

recommended that their use be limited to the preliminary screening of materials for field

testing.

21
The preliminary performance criteria are divided into three general categories:

5.1 — General Requirements of Stone Preservative Treatments

5.2 — Resistance of Preservative-Treated Stone to Specific Degradation Factors

5.3 — Resistance of Preservative-Treated Stone to Combinations of Degradation

Factors.

Important aspects of stone preservatives in each category are described by a performance

statement. Each performance statement consists of four parts [29].

(1) A Requirement, which states qualitatively what the stone preservative is to accomplish.

(2) A Criterion, or Criteria, which expresses quantitatively the levels of

performance needed to meet the Requirement.

(3) A Test, which describes how compliance with the Criterion, or Criteria, can be established.

(4) A Commentary, which may be added to explain or to clarify the Criterion.

The tests given in the following performance statements refer to the earlier sections

of the report where the tests are described in detail. The matrix given in table 11 can be

used as a guide in selecting tests and methods appropriate for evaluating a preservative's

performance once the cause of stone decay is known and properties needed from a preservative

treatment are identified. For example, if stone must be strengthened by a preservative,

the effectiveness of the preservative in doing this can be evaluated by measuring weight

changes, abrasion resistance, and surface hardness during testing. Tests and methods for

evaluating resistance to specific environmental causes of stone decay — the action of

chemicals, salt, water — can be selected in the same manner.

5. 1 General Requirements for Stone Preservative Treatments

5.1.1 Chemical Compatibility of the Stone Preservative with the Stone

Requirement. The preservative should not harm the stone or any building materials con- tiguous to, or embedded in the stone.

Criterion. The stone preservative should not contain any substances that will harm the

stone under the expected conditions of use, either upon application or with time.

22
Test 1. The chemical nature of the preservative should be determined, either by laboratory

tests or from information provided by the supplier. This information on the composition

should be reviewed by a consultant knowledgeable in stone decay, for its possible effect on the stone. A supplier who cannot divulge this information for a proprietary treatment

should guarantee compliance with the criterion.

Test 2. The acidity or basicity of the water phase obtained when the preservative is mixed

with an equal volume of distilled water should be within the pH range of 5 to 8.

Commentary. It is recommended that a list of the materials contiguous to or embedded in

the stone, or otherwise likely to be contacted by the preservative treatment, should be

given the supplier. He should describe the anticipated effects of the preservative treatments on these materials and recommend appropriate safeguards for protecting those materials

that would be degraded.

The literature survey and field inspections demonstrated the importance of knowing the

chemical nature of the stone preservative. The destructive chemical action of the preservative on the stone or the adjoining material is a serious problem. The deposition of soluble

salts or their formation in the stone by the preservative treatment is also to be avoided.

The chemical nature of a preservative should also be considered as to its compliance

with regulations covering worker safety and environmental protection.

5.1.2 Application of Stone Preservatives

Requirement. The stone preservative should be capable of being applied by the chosen

method(s), so as to give the expected results from the preservation treatment.

Criterion. The method (s) to be used in applying the stone preservative should give a uniform treatment of the stone when applied with the expected level of workmanship, under

the anticipated work conditions.

Test 1. The preservative supplier should specify practical methods of application; these

should be followed throughout the treatment. These methods should be (1) evaluated by an independent expert in stone preservation, or (2) examined by laboratory and/or field tests

by an agent of the user.

23
Commentary. The need for this Requirement and Criterion was apparent from literature

surveys and field inspections. The results obtained from a preservative treatment may be

dependent on how the treatment is carried out. This requirement is intended to minimize

the likelihood of improper application. It should be noted that any special storage

conditions (including shelf life), handling techniques, mixing directions, surface preparation, or safety precautions incident to the use of the preservative should be obtained

from the supplier and considered as part of the Test. It is strongly recommended that the

preservative be applied by workers experienced in applying it to stone. Further, before

application of the preservative, the stone should be cleaned by a cleaning procedure in

accord with the supplier's recommendations and all necessary repairs to the stone be

completed.

5.1.3 Absorption of the Stone Preservative by Stone

Requirement. The stone preservative should be adequately absorbed by the stone upon

application and should penetrate through any weathered surface layer of the stone. The

absorbed preservative should not detract from the appearance of the stone, either initially

or after a minimum period of on-site weathering for one year.

Criterion. Adequate absorption of the preservative by the stone is obtained if, when

applied by the intended method at the intended spreading rate, the appearance of the stone

after treatment is not less uniform than before treatment, and there are no signs of

unabsorbed preservative on the surface.

Test 1. Changes in appearance are assessed by either the subjective or instrumental methods

listed in Section 3.2.2.

Commentary. Once the preservative treatment is completed, objectionable differences in the

appearance of the treated stone may occur unless the stone preservative was uniformly

applied to and absorbed by the stone. Weathering can accentuate these differences. This

weathering should be for at least one year - longer, if possible. To help detect changes

in appearance, it is recommended that color photographs be taken of the stone test area before and after treatment, and again, after a minimum of one year's weathering under the

expected service conditions. Both supplier and user should evaluate all photographs and

agree on the acceptability of any changes in appearance. (A standard color chart included

in the test areas before photographing them will help detect color changes due to the color

film.)

24
5.1.4 Environmental Durability of Stone Preservative

Requirement. The stone preservative should withstand the environment to which it is to be

exposed for a sufficiently long time to be useful as a preservative.

Criterion. The preservative should not change in appearance or evidence degradation when

exposed, for the required test periods, to simulated or actual environments similar to those to which it will be exposed in use.

Test 1. Representative stone specimens should be treated with the preservative and exposed

to laboratory testing that simulates the predominant environmental factors encountered at the site where the preservative will be used (see Section 4) . When the predominant factors are unknown, a general test program will be used (see Section 3) . The duration of testing

and methods of evaluation will be defined by the test method being used.

Test 2. For on-site evaluation, an inconspicuous but representative area should be selected

for application of the preservative. This area should be exposed to the full effects of

the environment. Application of the preservative should follow the procedure recommended

by the supplier for large scale application. The area should be inspected and photographed

before and after application of the preservative, and periodically thereafter. After a minimum of one year, the test area should be evaluated for changes in appearance and

evidence of deterioration of either the preservative or the protected stone (see 5.1.3,

Commentary)

Commentary. Stone preservatives that have met laboratory criteria should be exposed also

to on-site weathering. Although the laboratory tests will involve conditions more stringent

than those found in natural weathering, only natural weathering will ensure that the

preservatives are exposed to all environmental factors, in their normal intensity and

combination. Whereas laboratory tests are done in relatively short times, defined by the

test procedure, it is recommended that on-site weathering tests be carried out for at least one year to allow exposure to all seasonal variations of the climate.

5.2 The Stability of Stone Preservatives Exposed to Specific Degradation Factors

5.2.1 Stability of Stone Preservative Treatments to Air-Borne Chemicals

Requirement. The preservative treatment should protect the stone from attack by air-borne

chemicals and remain unaffected by them for sufficiently long to be useful.

25
Criterion. Air-borne chemicals should not cause rapid physical changes nor changes in

appearance of the preservative treated stone or of the preservative treatment when tested

as described below.

Tests. As described in Section 4.1.

5.2.2 Stability of Stone Preservative Treatments to Salt Action

Requirement. Preservative treatments should protect the stone from salt action and be un- affected by the salts for sufficiently long to be useful.

Criterion 1. The stone preservative should protect the stone from deterioration due to salt crystallization within the stone for 10 test cycles when tested as described below.

Test. As described in Section 4.2.1.

Criterion 2. The stone preservative should prevent the penetration of the salt solution

into the stone for at least 3 test cycles when tested as described below.

Test. As described in Section 4.2.2.

Criterion 3. The preservative treated stone should not change in appearance or the preservative treatment be degraded when exposed for 6 months to a salt water atmosphere in the test described below.

Test. As described in Section 4.2.3.

5.2.3 Stability of Stone Preservative Treatment to Water Condensation/Evaporation

Requirement. The stone preservative should resist deterioration when exposed to cyclic

water condensation/evaporation.

Criterion. The surface of the preserved stone should not spall from the stone, decompose,

change in appearance, or otherwise deteriorate when exposed to 1200 test cycles of water

condensation/evaporation as described in the test below.

Test. As described in Section 4.3.

26
5.2.4 Stability of Stone Preservative Treatments to Solar Radiation

Requirement. The stone preservative treatment should not deteriorate rapidly during

exposure to solar radiation.

Criterion. The stone preservative treatment should not discolor or lose its effectiveness

when exposed to 500 test cycles of simulated ultraviolet radiation in the test described

below.

Test. As described in Section 4.4.

Commentary. Although the effect of ultraviolet radiation upon a preservative has been

considered only as to its effect upon the appearance of the preservative, visual changes

indicating changes in other properties should also be considered and evaluated when necessary -

the guide matrix (table 4) can be used in selecting appropriate procedures. Other test machines giving ultraviolet radiation of the intensity and wavelength of the machine described

in Section 4.4 may also be used.

5. 3 The Stability of Preservative Treated Stone to Combinations of Degradative Factors

Requirement. Preservative treated stone should withstand the expected degradative factors

significantly better than untreated stone.

Criterion 1. Weight Loss - Preservative treated specimens of stone should have a weight

loss no greater than 50% of the weight loss of untreated stone specimens when tested as described below.

Test. As described in Section 3.2.1.

Criterion 2. Appearance - Changes in appearance of the preservative treated stone specimens

should be less than that of untreated specimens when tested as described below.

Test. As described in Section 3.2.2.

Criterion 3. Water Absorption - The absorption of liquid water by treated stone specimens

should be no more than 50% of the water absorption of untreated specimens when tested as described below.

Test. As described in Section 3.2.3.

27
Criterion 4. Water Vapor Permeability - The water vapor permeability of preservative

treated stone specimens should not decrease more than 25% from the water vapor permeability

of untreated specimens when tested as described below.

Test. As described in Section 3.2.4.

Criterion 5. Abrasion Resistance - The abrasion resistance of preservative treated stone

specimens should be greater than that of untreated stone specimens when tested as described

below.

Test. As described in Section 3.2.5.

Criterion 6. Surface Hardness - The surface hardness of preservative treated stone specimens

should not decrease by more than 10% from the surface hardness of untreated specimens when

tested as described below.

Test. As described in Section 3.2.6.

Commentary. As discussed in Section 3.3, accelerated test procedures that combine several

causes of stone decay attempt to simulate their synergistic action, as in nature, but with

the drawback that the contribution of each degradation factor to the decay process cannot

be determined. The properties and test methods referred to in the above criteria and the

tests used in their evaluation can be applied to other methods simulating one or more

causes of stone decay, providing that the test specimen is of a size and shape that can be

used with the test instruments. Reference should be made to the matrix guide in table 13, to select those methods/tests that are appropriate to the needed requirement.

6. SUMMARY AND CONCLUSIONS

The development of preliminary performance criteria for selecting stone preservatives was the major goal of this program. This goal has been met through the recommendation of

nine preliminary performance criteria in three general categories and the test procedures

for establishing compliance with the criteria. Stone preservatives that meet the criteria

called for by the stone decay problem will be those most likely to give adequate performance.

28
The test methods which are given are intended to simulate, both singly and in combination,

the major causes of stone decay. A test which combines the most common causes of decay can be carried out with a special test chamber and selected evaluation procedures. Known test

procedures can be used for test methods involving single causes of decay, and for the

evaluation of both methods of testing.

It must be stressed that more remains to be done in stone preservative testing and

evaluation. Much remains to be learned about the mechanisms of stone decay and the effects

of stone preservatives on weathered stone. This knowledge may lead to the need of specific

methods for specific stones and for specific exposure conditions. Test methods based on a knowledge of the microstructure of the stone to be preserved might be of great assistance

in defining both the decay mechanisms and the most effective protective action. As new

information about stone preservatives and their effectiveness is obtained and new test

methods are developed, modifications may have to be made to the preliminary performance

criteria.

The present preliminary criteria offer three benefits to those who need to use stone

preservatives. First, they provide an objective basis for selecting stone preservatives,

both those now available and those to be developed in the future. Second, they direct

attention to properties that stone preservatives should have to be effective. Third, they

provide a standard approach to the testing - and selection - of stone preservatives which

field personnel can apply to their problems.

This research program leads to three conclusions for stone preservatives in general:

1. Test methods can be used to evaluate tentatively the performance of stone

preservatives.

2. None of the stone preservative materials evaluated fulfilled all the proposed

performance criteria.

3. A period of field testing must precede any large scale application of a stone preservative.

29
7 . ACKNOWLEDGEMENTS

People who have made major contributions to this program include:

Mr. Jack. Lee, Physical Science Aid at NBS , who did most of the laboratory testing

and evaluation work.

Dr. James Fearn, Research Chemist at NBS, who contributed to the testing phase

of the program.

Mr. Arthur Hockman, Materials Research Engineer at NBS, who initiated the

program and assisted throughout its duration.

It is not possible to mention individually the numerous people at the National Bureau

of Standards and in the National Park Service who have given advice and assistance during

this project; they must be thanked collectively.

The generosity of the various suppliers and manufacturers who contributed their

products to the testing program must also be noted.

Mr. Janez Krzan, Chemical Engineer at the Institute for Materials Research, Ljubljana,

Yugoslavia, during his stay at NBS also contributed in developing certain parts of the

testing program.

30
8. BIBLIOGRAPHY

1. Sneyers, R. , "Stones Also Die," UNESCO Courier, _18, 26 (1965).

2. Winkler, Erhard M. , Stone: Properties, Durability in Man's Environment , SpringerVerlag, New York (1973), p. 88.

3. "Air Pollution is Eroding World's Stone Art," The New York Times , April 13, 1964, p. 1.

4. Riederer, Josef, "The Conservation of German Stone Monuments," The Treatment of Stone , editors, R. Rossi-Manaresi, and G. Torraca, Centro per la Conservazione delle

Sculture All'Aperto, Bologna (1972), p. 112.

5. RILEM Committee 6-PAN, "Tentative Recommendations: Testing Methods for Natural and

Artificial Stones," Materiaux et Constructions, _5, 231-245 (1972).

6. New York Conference on Conservation of Stone and Wooden Objects, 7-13 June 1970,

London: International Institute for Conservation of Historic and Artistic Works.

7. Meeting of the Joint Committee for the Conservation of Stone, IC0M/IC0M0S, Bologna,

October 1-3, 1971, Bologna, Italy.

8. First International Symposium on the Deterioration of Building Stones, 11-16 September

1972, La Rochelle, France.

9. Winkler, op. cit . , p. 187.

10. Lewin, Seymour Z., "The Preservation of Natural Stone, 1839-1965, An Annotated

Bibliography," Art and Archaeology Technical Abstracts, 6_, 185-277 (1966).

11. NBS Special Publication 361, "Performance Concept in Buildings," Joint RILEM-ASTM-CIB

Symposium, 2-5 May 1972, Philadelphia, U.S. Government Printing Office, Washington,

DC (1972).

12. Sleater, Gerald A., "A Review of Natural Stone Preservation," NBSIR 74-444, U.S.

Department of Commerce, Washington, DC (1973)

13. D'Ossat, Guglielmo De Angelis, Guide to the Methodical Study of Monuments and Causes of

their Deterioration , International Centre for the Study of Preservation and Restoration

of Cultural Property: Rome (1972), p. 12.

31
14. Winkler, op_. cit .

15. Oilier, Cliff, D., Weathering , American Elsevier Publishing Co., New York (1969).

16. Winkler, o£. cit., pp. 119-125.

17. Winkler, op_. cit . , pp. 89-94.

18. Schaffer, R. J., The Weathering of Natural Building Stone , Special Report Number 18 of

the Department of Scientific and Industrial Research London: His Majesty's Stationary

Office (1932), p. 28.

19. Winkler, op. cit . , pp. 145-147.

20. Winkler, op_. c_it . , pp. 125, 172.

21. Bowles, Oliver, The Stone Industries, McGraw-Hill, New York (1939), p. 38.

22. Warnes, Arthur R. , Building Stones, Their Properties, Decay, and Preservation , London:

Ernest Benn Ltd. (1926), pp. 251, 256-259.

23. Kamal, R. , and Saxon, R. , "Analysis and Prediction of Weatherability," Applied Polymers

Symposia, Weatherability of Plastic Materials , Number 4, pp. 1-29 (1967).

24. Mamillan, Marc, Pathology of Building Materials , International Centre for the Study of

the Preservation and the Restoration of Cultural Property, Rome (1970), pp. 14-15.

25. Schaffer, £p. £it . , p. 91.

26. NBSIR 75-789, "Graffiti-Resistant Coatings: Methods of Test and Preliminary Selection

Criteria," by M. Godette, M. Post, and P. Campbell; NBSIR 75-914, "Graffiti Removers:

Evaluation and Preliminary Selection Criteria," by M. Godette, M. Post, and P. Campbell.

27. NBS Technical Note 883, "Waterproofing Materials for Masonry," by E. Clark, P. Campbell,

and G. Frohnsdorff.

28. Copies of individual DIN test methods may be obtained from Beuth-Vertrieb Gmbh, 1 Berlin 30, Burggrafenstrasse 4-7.

32
29. Commins, R. T. and Waller, R. E., "Observations from a Ten-Year Study of Pollution at

a Site in the City of London," Atmospheric Environment , Vol. 1, Pergamon Press: London

(1967), pp. 49-68.

30. Activities outside the Federal Government may obtain copies of Federal Standards as outlined under the General Information in the Index of Federal Specifications and

Standards and at prices indicated in the Index. The Index, which includes cumulative

monthly supplements as issued, is for sale on a subscription basis by the Superintendent

of Documents, U.S. Government Printing Office, Washington, DC, 20402. Federal Government

activities may obtain copies of Federal Standards from established distribution

points in their agencies.

31. Stambolov, T. and van Asperen de Boer, J. R. J., The Deterioration and Conservation of

Porous Building Materials in Monuments , International Centre for the Study of Preservation and Restoration of Cultural Property: Rome (1972), p. 21.

33
APPENDIX A - CONFORMANCE OF STONE PRESERVATIVES TESTED TO CRITERIA

The purpose of the testing phase of the program was to use the test data and experimental

procedures to develop preliminary performance criteria that could be used to select stone

preservatives. The materials tested as preservatives were evaluated as to their performance.

Two tables have been drawn up to summarize the performance of each material tested in the

program, both in combined testing and in individual tests. They are:

Table 12 — Results for General Testing (section 3)

.

Table 13 — Results for Individual Testing (Section 4)

.

In each table, the numbers in the left hand column refer to the code numbers given

each preservative. The column headings refer either to the change in property evaluated

(Part 3, general testing), or to the specific test carried out (Part 4, individual testing).

Performance is expressed in one of three ways:

X — the preservative met the criterion given in Part 5. blank space — the preservative did not meet the criterion.

N.T. — the preservative was not tested.

The test data used in developing these tables should be accepted as valid only within

the conditions of the test program.

These tables are intended only as a guide to selecting preservative materials for

field application. It should be stressed that no one preservative met all performance

criteria . Where a preservative has met the criterion or criteria relevant to a need in

stone preservation, its use can be tentatively recommended. However, in all applications,

preliminary field testing in situ will be necessary to adequately judge the material's

performance.

34
TABLE 1. Stone Preservative Materials (2.4)

Stone NonPreservative Compositional Volatile

Code II Type Content color; miscibility with water

Liquid Preservative Dry Preservative

color; physical state

01

02

03

04

05

06

08

09

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

Silicone

Silicone

Methyl

Methacrylate

Methyl

Methacrylate

Silicone

Silicone

Methyl

Silicone

Methyl

Silicone

Methyl

Silicone

Methyl

Silicone

Methyl

Silicone

Methyl

Silicone

Methyl

Silicone

Methacrylate

Polymer

Methacrylate

Polymer

Methacrylate

Polymer

Inorganic

Inorganic

Inorganic

Methyl

Silicone

Methyl

Silicone

Polyisobutyl

Methacrylate

Acrylic

Polymer

Acrylic

Polymer

6.6% water-white; immiscible

16.7% water-white; immiscible

20.7% white, opaque; miscible

18.5% white; miscible

10.0% water-white; immiscible

12.5% water-white, miscible

6.7% water whit2; miscible

80.0% water-white; immiscible

33.0% water-white; miscible

(pH > 11)

53.0% water-white; viscous,

immiscible

53.0% white; miscible

37.0% water-white; immiscible

6.6% water-white; immiscible

27.0% water-white; immiscible

30.0% water-white; immiscible

39.0% water-white; immiscible

26.0% water-white; miscible,

pH > 11

47.0% water-white; miscible,

pH 1 45.0% water-white; miscible,

pH 3 55.0% water-white; immiscible

23.0% water-white; immiscible

33.0% colorless; immiscible

23.0% water-white; immiscible

10.0% water-white; immiscible

35

colorless; adherent,

flexible film

colorless; hard,

brittle film

pale-white; flexible

film

orange; brittle film

white; crumbly film

did not dry

pale yellow; brittle

film

colorless; brittle

film

white; brittle film

white; waxy solid

colorless; sticky

film

brown; crumbly,

granular solid

flexible, sticky mass

colorless ; flexible

film

pale white; tough,

adherent, britle film

white; crystalline

solid

dark brown; powder

colorless; pliable

film

colorless; brittle

film

colorless; brittle

film

white; crumbly film
TABLE 1. Stone Preservative Materials (continued)

Stone NonPreservative Compositional Volatile

Code # Type Content

Liquid Preservative Dry Preservative

color; miscibility with water color; physical state

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

Acrylic

Polymer

Methyl

Silicone

Methyl

Silicone

Polyisobutyl

Methacrylate

AcrylicEpoxy

Sodium Methyl

Siliconate

Acrylic

Polymer

Acrylic

Polymer

Acrylic

Polymer

Plastic

Emulsion

Plastic

Emulsion

Sodium Methyl

Siliconate

Inorganic

Acrylic

Copolymer

10.0% water-white; immiscible

23.0% water-white; immiscible

55.0% water-white; immiscible

31.0% water-white; immiscible

39.0% water white; miscible

33.0% water-white; miscible,

pH > 11

10.0% water-white; immiscible

27.0% water-white; solidified

with HO

21.0% water-white; immiscible

10.0% water-white; immiscible

3.0% green-white; miscible

28.0% white; immiscible

31.0% water-white; miscible,

pH > 11 — water-white; miscible,

pH > 10

20.0% water-white; immiscible

Silicone 4.9%

Acrylic Resin 30.0%

Fluorocarbon 2.0%

water-white; immiscible

water-white; immiscible

water-white; immiscible

Fluorocarbon 11.0% water-white; ppt with water

Fluorocarbon 18.0%

Fluorocarbon 2.0%

Linseed Oil 103.0%

white; miscible

water-white; miscible

amber; immiscible

cream colored; powder

colorless; brittle

film

colorless; pliable

film

pale yellow; flexible

film

white; powder pH > 11

water-white; flexible

film

colorless; adherent

flexible, tough film

colorless; flexible

film

clear, dry, adherent,

flexible film

bluish; flexible

film

faint yellow; tough,

flexible film

does not dry

colorless; flexible,

tough film

colorless; clear,

flexible film

colorless; clear,

brittle film

yellow; brittle film

colorless; brittle film

does not dry

36
TABLE 1. Stone Preservative Materials (continued)

Stone NonPreservative Compositional Volatile Liquid Preservative Dry Preservative

Code # Type Content color; miscibility with water color; physical state

49 Sodium 56.0% water-white; miscible HO colorless; brittle

Silicate, pH > 11 film

40° Baume

50 Tetraethyl 0.0% water-white; immiscible

Ortho-Silicate

51 Acrylic 47.0% white; miscible white; flexible,

Resin tough film

52 Methyl 7.0% pale red-yellow; miscible faint yellow; brittle

Silicone film

53 Calcium — water-white; pH > 14

Hydroxide

54 Ba (OH) + 30.0% water-white; pH > 14 additives

55 Fluorocarbon

56 Fluorocarbon

37
TABLE 2. Stone Preservative Treatments of Indiana Gray Limestone.

Untested Stone: color; feel; weight changes; depth penetration

of preservative. Stone Tested in CAD: color; feel; weight change.

(2.4)

Stone

Preservative

Untested Stone

(color; feel; wgt. change;

penetration)

Stone Tested in CAD

(color; feel; wgt. change)

10 cycles 20 cycles

00

01

02

03

04

05

06

08

09

10

11

12

13

14

15

16

17

18

19

light gray; smooth

dark gray; smooth;

+0.13%; 4 mm

medium gray; smooth;

+0.72%; —

light gray-brown,

glossy; smooth;

+0.27%; <1 mm

mottled orange, slight

gloss; smooth; +0.24%;

1 mm

light gray-brown;

+0.22%; 2 mm

dark brown; smooth;

+0.50%; —

light gray-brown,

slight gloss;

+0.15%; <1 mm

dark brown; +1.98%;

8 mm

dark gray; smooth

+0.77%; 8 mm

light gray; +0.05%;

<1 mm dark gray; smooth;

+0.49%; 9 mm

dark brown; smooth;

+0.69%; 3 mm

dark gray; smooth;

+0.06%; 3 mm

dark brown; smooth;

+0.23%; 1 mm

dark brown; smooth

+0.32%; <1 mm

dark brown-gray,

gloss; smooth;

+0.35%; 2 mm

light brown; smooth;

+0.63%; 5 mm

light brown; smooth;

+0.46%; <1 mm

orange-brown; rough;

-1.16%

light orange; rough;

-0 . 38%

light gray-brown;

rough; —

light gray-brown;

smooth; -0.09%

orange; —

;

-0.78%

light orange; smooth;

-0.45%

light brown; smooth;

-1%

dark brown, no gloss;

-0.56%

light brown; rough;

-0.77%

light brown; rough;

light orange; rough;

-1.02%

orange coating; smooth;

-0.68%

orange; smooth; -0.53%

light orange; smooth;

-0.61%

light brown coating;

smooth; -0.24%

light brown; smooth

-0.19%

medium brown, no gloss;

smooth; -0.59%

light brown; rough;

-.40%

light brown; smooth;

dark brown; rough

-2.06%

light brown;

rough; -1.43%

light orangebrown; rough;

-1.93%

light orangebrown, no gloss;

smooth; -0.29%

dark brown; rough:

-2.16%

dark orange;

smooth; -0.98%

orange-brown

;

rough; -2.10%

dark orange;

rough; -1.27%

light brown;

rough; -1.73%

light brown;

rough; -2.13%

orange color;

rough; -0.97%

orange; rough;

-2.14%

dark orange;

rough; -1.44%

dark orange;

smooth; -1.10%

light brown;

smooth; -0.63%

light brown;

rough; -0.62%

light brown;

smooth; -1.68%

light brown;

rough; -2.1%

Weight changes: + means increase in weight. 38
TABLE 2. Stone Preservative Treatments of Indiana Gray Limestone.

Untested Stone: color; feel; weight changes; depth penetration

of preservative. Stone Tested in CAD: color; feel; weight change.

(2.4) (continued)

Stone

Preservative

Untested Stone

(color; feel; wgt. change;

penetration)

Stone Tested in CAD

(color; feel; wgt. change)

10 cycles 20 cycles

20

21

22

23

24

25

26

29

30

31

32

33

34

35

36

37

38

40

light gray; smooth; —

<1 mm

dark brown, gloss;

smooth; +0.75%; 1 mm

medium brown; smooth;

+0.53%; —

light brown, gloss;

+0.36%; —

light gray-brown; smooth;

+0.37%; <1 mm

light brown; smooth;

+0.04%; 4 mm

light gray; smooth;

+0.15%; 5 mm

dark brown, gloss;

smooth; +0.30%; —

dark gray, gloss;

smooth; +0.23%; <1 mm

light brown; smooth;

+0.96%; 6 mm

medium brown; smooth;

+0.10%; 6 mm medium brown, gloss;

smooth; +0.44%; 3 mm

medium brown, gloss;

smooth; +0.32%; <1 mm

medium brown, gloss;

smooth; +0.11%; <1 mm

dark gray; smooth;

+0.20%; <1 mm

light brown, gloss;

smooth; +0.44%; < 1 mm

medium gray; smooth;

+0.34%; 8 mm

medium brown, gloss;

smooth; +0.34%; <1 mm

light gray; smooth

light brown; rough

-0.22%

light brown; rough

-0.98%

light brown, no gloss;

smooth; -0.43%

light gray-brown;

smooth; -0.08%

light brown; smooth;

-1.54%

light orange; rough;

-0.88%

dark gray, gloss;

smooth; -0.49%

light brown; rough;

-0.97%

dark brown, some gloss; smooth; -0.40%

orange-brown; rough;

-1.09%

medium brown, no gloss;

smooth; -0.20%

dark orange; mottled;

rough; -0.49%

light gray; rough;

-0.23%

light gray; smooth;

light brown, gloss;

rough; -0.15%

orange; smooth;

-1.70%

light orange

surface; -0.48%

light brown;

rough; -1.95%

light brown, no gloss; smooth;

-0.25%

light gray-brown;

smooth; -0.12%

light brown;

smooth; -0.45%

dark orange;

rough; -2.04%

medium brown,

no gloss; rough;

-0.23%

dark gray, gloss;

smooth; -1.90%

dark brown; rough;

-1.22%

light brown;

smooth; -0.83%

dark brown, no gloss; smooth;

-0.22%

dark brown; rough;

-1.88%

medium brown;

smooth; -0.29%

medium orange;

rough; -0.95%

light gray;

rough; -0.34%

gray-brown;

rough; -1.81%

light brown, no gloss; rough;

-0.43%

39
TABLE 2. Stone Preservative Treatments of Indiana Gray Limestone.

Untested Stone: color; feel; weight change; depth penetration

of preservative. Stone Tested in CAD; color; feel; weight change.

(2.4) (continued)

Untested Stone Stone Tested in CAD

Stone

Preservative

(color; feel; wgt. change;

penetration)

(color; feel; wgt. change)

10 cycles 20 cycles

41

42

43

44

45

46

47

49

50

51

52

53

54

55

57

58

light gray; smooth;

+0.11%; <1 mm

light brown; smooth;

+0.18%; 3 mm

light gray; smooth;

+0.03%; 1 mm

light gray; smooth;

+0.15%; 1 mm

light gray; smooth;

+0.17%; <1 mm

light gray; smooth;

+0.01%; 1 mm

dark brown; smooth;

+1.41%; 6 mm

dark gray; smooth;

+0.94%; <1 mm

light gray; smooth;

+0.05%; <1 mm

medium gray, gloss;

smooth; +0. 75%; <1 mm

dark gray; smooth;

+0.22%; <1 mm

light gray; smooth

+0.01%; —

light brown; smooth;

+1.25%

light brown; smooth; — ; 3 mm

dark gray; smooth; — ; 5 mm

dark brown; smooth; — ; 10 mm

light brown; rough;

-0.56%

orange; rough; -1.33%

light brown; rough;

-0.93%

light gray; rough;

-0.09%

light gray; smooth;

-0.19%

orange-gray; rough;

-0.24%

light orange; smooth;

-1.37%

dark gray; rough;

-2.1%

light brown; rough;

-1.63%

medium gray, some

gloss; smooth; +0.28%

light orange; rough;

-0.96%

light brown-gray;

smooth; -0.54%

light brown; smooth;

-0 . 88%

light orange-brown;

smooth; -0.35%

orange; smooth;

-0 . 04%

dark orange;

rough; -2.17%

orange; rough;

-1.82%

orange; rough;

-2.05%

orange; rough;

-0.62%

orange-gray;

smooth; -0.57%

light brown;

rough; -1.93%

dark orange;

rough; -1.59%

orange-gray;

rough; -3.90%

medium brown;

rough; -2.8%

medium gray, some

gloss; smooth;

+0.06%

dark orange;

rough; -1.42%

medium brown;

rough; -1.54%

dark brown; smooth;

-2.01%

orange; smooth;

-0.76%

orange; rough;

-0.92%

orange; smooth;

-0.09%

40
TABLE 3. CAD Test Cycle (3.1)

Overnight — Specimens stored in deep-freeze at -40°C. (16 hours)

8:30 — Specimens removed from deep-freeze, mounted on drum of CAD.

8:30-10:00 — Specimens rotated with lamps (6-UV, 3-IR) on — specimens'

surface temperature reaching 50°C. (1 1/2 hours)

10:00 - 10:30 — Water spray on, continued rotation of specimens with lamps on. (1/2 hour)

10:30 - 11:00 — Water spray off; continued rotation of specimens with lamps on. (1/2 hour)

11:00 - 16:00 — Lamps on, CAD drain closed; 3% sodium chloride/0.01 molar

sulfurous acid solution pumped into CAD, specimens rotated,

passing through solution for 1/8 of rotation. (5 hours)

16:00 - 16:30 — Lamps off, continued rotation of specimens. (1/2 hour)

16:30 — CAD drained, specimens removed and returned to deep-freeze for

overnight storage.

41
TABLE 4. Contribution of Each Feature of the CAD to Simulated Stone Decay

—~^^ Feature of CAD

"""---^^^ Test

Simulated Cause --^^^

of Stone Decay ~""~^^^

uvLamps

IRLampsWater

Spray

Water

Soak

Sulf urous Acid Soak

Salt

Soak

Deep

Freeze

Water Action X X X X X

Chemical Attack X X

Salt Action X X X

Thermal Effects X X X

Solar Radiation X X

42
TABLE 5. Result of Specimens Exposed to 49 Cycles Sulfurous

Acid Testing (4.1)

00

01

02

03

04

05

06

08

09

10

11

12

15

16

17

18

19

20

21

22

23

24

25

26

* - white surface

original color lost

blistering of surface

* - white surface

flaking of preservative

white surface

white surface

* - surface residue

discoloration

*

white surface

no change

28 white surface deposit

29 surface deposit

30 blistering of surface

31 white surface

32 white surface

33 discoloration

34 discoloration, flaking of

preservative

35 white surface

36 no change

37 no change

38 *

39 blistering of surface

40 *

41 *

42 surface deposit

43 *

44 no change

45 *

46 white surface deposit

47 fading of color

49 brittle, cracked surface

51 discolored

52 surface deposit

53 mottled appearance

c small acicular crystals on specimen surface

43
TABLE 6. Sodium Sulfate Crystallization Test (4.2.1)

(Cumulative percent weight loss of specimens)

Stone

Preservative 1 2 3 4 Test Cyc5 les

6 7 8 9 10

00 +2 -1 -8 -16 -21 -25 -29

01 +1 +1 +1 +1 +1 -1 -1 -8 -17 -27

02 -1 -1 -1 -1

03 +2 +2 +3 -2 -12 -20 -26

04 +3 +3 +2 -2 -5 -7 -10 -12 -23 -28

05 +1 +1

06 +2 +3 +3 +2 +3 +2 +1 +4 -11 -20

08 +1 +3 +3 +12 -20 -25 -29

09

10

11 +1 -1 -8 -11 -14 -17 -21 -25

12 +2 +1 -2 -8 -15 -9 -10 -15 -17 -17

13 +2 +1 +1 -4 -10 -15 -23 -26

14 +2 +1 -3 -4 -5 -5 -6 -13 -15 -15

15 +1 -17 -24 -25

16 +1 +1 -14 -15 -17 -23 -34

17 +1 -9 -24 -30

18 -1 -4 -6 -12

19 +1 +1 +2 +1 -4 -10 -15 -17 -23 -26

20 +1 +1 +1 -1 -5 -9 -11 -13 -14 -15

21 +1 +1 +1 +1 -11

22 +1 +1 +1 -1 -6

23 +4 +4 +5 +3 +1 +1 -1 -6 -10 -11

24 +1 -1 -6 -22

25 +1 +1 +1 +1 -8

26

29 +1 +3 +4 +2 -5 -13 -19 -24 -29

30 +3 +3 +4 +4 +4 +5 -5 -13 -19 -21

31

32 +3 +2 +1 -1 -8 -23 -30

33 +2 +2 -8 -20 -25

34 +2 -2 -3 -15 -24 -29

35 +3 -3 +3 -2 -5 -8 -13 -16 -20 -24

36 +2 +2 -3 -4 -34

37 +1 +2 +2 -5 -9 -24 -32

38 +1

39 +1 +1 +2 +2 +2 +2 +2 +2 +2 +2

40 +7 +3 -5 -8 -10 -12 -14 -19 -25

44
TABLE 6 . Sodium Sulfate Crystallization (continued)

Stone

Preservative 1 2 3 4 Test Cycl5 es

6 7 8 9 10

41 +1 +2 -2 -5 -16 -25

42 +2 +3 +1 -1 -4 -7 -9 -12 -18 -37

43 +1 +1 -5 -15 -21 -27

44 -4 -6 -8 -12 -16 -24 -31

45 +1 +2 -3 -11 -20 -29

46 +1 +1 -1 -12 -23 -25

47 +1 +1 +2 +2 +2 +1 +1 +1 +1 +1

49 +2 +2 +1 -2 -5 -8 -11 -18

50 +1 +2 -2 -4 -5 -8 -10 -11 -13

51 +1 +2 +3 +3 +2 +3 +4 +2 -26

52 +1 +2 +2 -4 -13 -20 -28

53 +2 +2 -4 -8 -14 -19 -23 -29

54 +2 +2 +3 +3 +3 +3 +3 +2 +2 +1

45
TABLE 7. Sodium Sulfate Penetration Test (4.2.2)

Condition of dry test specimens after three test cycles.

Top of specimen untreated, other five sides treated with

stone preservative

Stone Condition of St one Condition of

Preservative Specimen Preservative Specimen

00 top degraded 27 NC*

01 NC 28 efflorescence on top

02 NC 29 sides spalling

03 top degraded; sic es sp ailing 30 top degraded

04 top degraded 31 NC

05 NC 32 top degraded

06 NC 33 sides spalling

08 top degraded; sic es sp ailing 34 sides spalling

09 NC 35 sides spalling

10 NC 36 top degraded

11 top degraded 37 top degraded; sides spalling

12 NC 38 NC

13 top degraded 39 NC

15 NC 40 top degraded; sides spalling

16 NC 41 efflorescence on top

17 sides spalling 42 sides spalling

18 NC 43 top degraded; sides spalling

19 efflorescence on top 44 sides spalling

20 efflorescence on top 46 sides spalling

21 top degraded 47 NC

22 NC 49 NC

23 top degraded 50 top degraded

24 top degraded; sic es Sp ailing 51 top degraded

25 NC 52 efflorescence on top

26 NC 53

54

top degraded; sides spalling

NC

NC no change in specimen.

46
TABLE 8. Water Absorbed by Specimens During

Condensation/Evaporation Testing (4.3)

Stone Preservative Percent Weight Gain

00 6.3

03 6.7

04 5.2

06 4.8

08 5.1

11 5.4

12 1.4

13 4.7

14 4.0

19 5.2

20 4.8

30 3.6

32 3.7

34 5.6

35 3.5

36 6.3

37 6.6

42 4.3

45 5.4

47 4.5

49 5.1

50 5.9

51 5.0

52 5.9

53 5.7

54 4.3

47
TABLE 9. Surface Deposits on Specimens After Water

Evaporation/Condensation Testing (4.2.1)

Stone Preservative

04

Description of Surface Deposit

White deposit on sides of specimen

above wet zone.

20 Dark deposits on sides of specimen

above wet zone.

34 Very large white surface deposit on untreated surface of specimen.

36 Small white deposits on sides of

specimen above wet zone.

37 White crust covering untreated

surface.

47 Dark orange discoloration on sides

of specimen above wetted zone.

50

51

White deposits on ends of specimen.

Spalling of preservative coating

along untreated surface.

54 White deposits on untreated surface.

48
TABLE 10. Stone Preservatives Which "Yellowed" After Exposure to 1100 Hours Radiation in a Xenon-Arc Weathering Apparatus (4.4)

Stone Preservative Generic Composition

04 Methyl Methacrylate

05 Silicone

08 Methyl Silicone

15 Methacrylate Polymer

16 Methacrylate Polymer

19 Inorganic Composition

20 Inorganic Composition

33 Acrylic Polymer

34 Acrylic Polymer

35 Organic Resin

40 Acrylic Copolymer

42 Unknown

47 Linseed Oil

49
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50
TABLE 12. Extent to Which Stone Preservatives Met, After 20 Cycles of CAD

Testing (Section 3\ the Preliminary Performance Criteria of Section 5 (see Appendix A)

Stone Weight Water Water Vapor . Abrasion Surface

Preservative Appearance Loss Absorption Permeability Resistance Hardness

1 X* X X

2 X X

3 X X X X

4 X X

5 X X X X

6 X X X

8 X X

9 X X

10 X X X

11 X X X

12 X N.T. ** X X

13 X X

14 X X X

15 X X

16 X X X

17 X X X

18 X X X

19 N.T. X X X

20 X X X

21 X X

22 X X X

23 X X X

24 X

25 X

26 X X N.T. X

27 N.T. N.T. N.T. N.T. N.T.

28 N.T. N.T. N.T. N.T. N.T.

29 X X X X

30 X

31 X X

32 X X N.T. X

33 X X X

34 X

35 X X

36 X X X

* X = met criteria.

** N.T. = not tested.

51
TABLE 12. CAD Testing ( 20 eye les) (continued)

Stone Weight Water Water Vapor Abrasion Surface

Preservative App earance Loss Absorp tion Permeability Resistance Hardness

37 X

38 X X

39 N.T. N.T. N.T. N.T.

40 X X

41 X X X

42 X X X

43 N.T. N.T. X

44 X X

45 X X

46 X N.T. X

47 X X

49 X X

50 X X

51 X N.T. N.T.

52 X X

53 X X X

54 X X

55 X X X X

57 X X X

58 N.T. X

52
TABLE 13. Extent to Which Stone Preservatives Met, for Individual Test Methods

(Part 4), the Preliminary Performance Criteria of Section 5. (see Appendix A)

Water Sodium Sodium Sulfurous Sodium

Stone Condensation/ Sulfate Sulfate Ultraviolet Acid Chloride

Preservation Evaporation Crystallization Penetration Radiation Fog Fog

1

2

3

4

5

6

8

910

11

1213

14

15

16

1718

19

20

21

22

23

24

25

26

2728

29

30

31

32

33

34

35

36

X*

X

X

XX

X

XX

XX

X

X

X

X

XX

X

X

XX

XX

XX

X

X

XX

X

X

X

N.T.

N.T.

X X X X X X X X

X X X X X X

X

X X X X X X

X X

X X X N.T.** N.T,

N.T. X N.T. N.T

X X X X

X X

X X X

XX X X

X X X

X X X X X X X X

X X X X X X X X X X X X X X X

X XX

X

X

X X X

* X = met criteria.

** N.T. = not tested.

53
TABLE 12. Results for Individual Testing (see Appendix A) (continued)

Water Sodium Sodium Sulfurous Sodium

Stone Condensation/ Sulfate Sulfate Ultraviolet Acid Chloride

Preservation Evaporation Crystallization Penetration Radiation Fog Fog

3738 X X

39 N.T. X

40- X

41 X

42 X

43 X

44 X

45 X

46 X

47 X

49 X

50

51

52 X

53 X

54 X

55 N.T.

57 N.T. N.T.

58 N.T. N.T.

X X X

X X X X N.T. X

X

X X

X

X X

X X X

N.T. X X

X X

N.T. X X X

X N.T. X

X X

X N.T

X N.T

X X N.T. X

N.T. N.T. N.T. X

N.T. N.T. N.T. N.T

N.T. N.T. N.T. N.T

54
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Figure 2. Penetration of Stone Preservative into

Indiana Limestone (2.4): Section of stone specimen

treated with stone preservative; black line indicates

depth of penetration of preservative.

56
I.4M

A - HEAT 8 ULTRAVIOLET LAMPS

B - WATER SPRAY

C - ROTATING SPECIMEN DRUM

D - FIFTEEN STONE SPECIMENS MOUNTED ON ONE FACE OF SPECIMEN DRUM

E - MOTOR 8 GEAR TO ROTATE SPECIMEN DRUM AT I RPM

F - INLET FOR CORROSIVE TEST SOLUTIONS

G - OUTLET FOR STORAGE OF CORROSIVE TEST SOLUTIONS

H - OUTLET TO DRAIN

Figure 3. Chamber for Accelerated Decay (CAD) Section 3.1.

57
Figure 4. Change in Appearance (3.2.2): Slight

change in appearance of treated stone. Top row untreated limestone specimen; limestone treated

with preservative 09. Bottom row — limestone

specimens treated with preservative 09 after 10

and 20 CAD test cycles respectively.

*2 20 cycles CAD *

Figure 5. Change in Appearance (3.2.2): Extreme

change in appearance of the treated stone. Top row — untreated limestone specimen; limestone

specimen treated with preservative 34. Bottom

row — limestone specimens treated with preservative 34 after 10 and 20 CAD cycles, respectively.

58
Figure 6. Change in Appearance (3.2.2): Change

in appearance through loss of preservative coating.

Top row — untreated limestone specimen; limestone

specimen treated with preservative 37. Bottom row limestome specimens treated with preservative 37,

after 10 and 20 CAD cycles respectively.

20 cycles CAD

Figure 7. Change in Appearance (3.2.2): Close-up of

surface of stone specimen treated with preservative 37,

exposed 20 CAD cycles, from Figure 6.

59
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61
Figure 10. Water Vapor Permeability (3.2.4): Cups

used for water vapor permeability measurement —

A) empty cup; B) cup with desiccant; C) cup with

specimen attached with adhesive aluminum tape. (Cups

approximately 10 cm on edge.)

62
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63
Figure 12. Abrasion Resistance (3.2.5): test machine —

A) 1 kg test loads; B) grinding wheels; C) stone test specimen; D) adjustable sides to hold specimen on rotating

table.

64
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39 40 41 42 43 44 45 46 47 49 50 52 53 54 55 57. 58 STONE PRESERVATIVE

66
A - TEST CABINET

B - GAS CYLINDER

C - GAS MEASURING CONTAINER

D - GAS INLET VALVE

E -- LOW PRESSURE SAFETY VALVE

F - HIGH PRESSURE SAFETY VALVE

SULFUROUS ACID FOG TEST

Figure 15. Sulfurous Acid Fog (4.1); Representation of test cabinet

used in sulfurous acid fog test.

67
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68
Figure 17. Sulfurous Acid Test (4.1): treated limestone

specimens exposed to 49 cycles of sulfurous acid testing.

Top row — treated but unexposed test specimens. Bottom

row — exposed specimens with same preservative treatment

as the unexposed specimens above them.

Figure 18. Concentrations of Sulfurous Acid Used in Testing

(4.1): Indiana limestone (standard gray) exposed 4 hours to flow of sulfur dioxide saturated water solution over surface

(flow rate, 5 ml/min) . Weight loss of specimen, -2.50%.

Depth of erosion, 2 millimeters. Experiment run at 22°C.

69
+ 5%

-20%

-25% -

4 5 6 TEST CYCLES

Figure 19. Sodium Sulfate Crystallization (4.2.1): Height changes

in stone preservative treated specimens exposed to sodium sulfate

crystallization test. Specimen A — unaffected after 10 test cycles;

specimen B — onset of degradation after 6 test cycles; specimen C —

onset, then gradual degradation after 1 test cycle; specimen D —

onset of degradation after 2 test cycles.

70
Figure 20. Sodium Sulfate Crystallization (4.2.1): Specimens

exposed to varying lengths of cycles of sodium sulfate crystallization test. A) — preservative treated specimen, intact after

10 test cycles; B) — preservative treated specimen, preservative coating flexible when wet, stone degraded within preservative shell; C) preservative treated specimen, beginning to degrade after 10 test cycles (arrows indicate spalling and cracking preservative treated layer) ; D) untreated limestone after

3 test cycles.

Figure 21. Sodium Sulfate Penetration (4.2.2): Top, untreated

surface of preservative treated specimen after 3 test cycles

of sodium sulfate penetration. (Arrows indicate spalling layers

of preservative treated stone.)

71
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72
A - TEST SPECIMENS

B WATER BATH

C -- DUCT FOR FORCED AIR DRYING

17 cm

WATER EVAPORATION / CONDENSATION TEST

Figure 23. Water Condensation/Evaporation (4.3)

Schematic of water bath used in tent.

73
Figure 24. Water Condensation/Evaporation (4.3): degradation

and transport of stone preservative treatment by water condensation/

evaporation testing (2400 cycles) . Side view of specimen. Arrows

indicate direction of water migration from bottom, coated surface

of specimen to the top, uncoated surface.

74
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-%1

2. Gov't Accession

No.

4. TITLE AND SUBTITLE

Stone Preservatives: Methods of Laboratory Testing and

Preliminary Performance Criteria

3. Recipient's Accession No.

5. Publication Date May 1977

6. Performing Organization Code

7. AUTHOR(S)

Gerald A. Sleater

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

National Park Service

U.S. Department of the Interior

Washington, DC 20240

13. Type of Report & Period Covered Final Report

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) Although numerous materials have been proposed as preservatives for stone in historic

buildings and monuments, their efficacy is difficult to establish. In the work

described here, a laboratory research program of accelerated simulated stone decay was

used to obtain data on stone preservatives and to suggest criteria for their selection.

Over 50 materials usable as stone preservatives were tested.

Tests to simulate stone decay were of two types:

1. exposure to combined weathering factors using a special test chamber for

accelerated decay (CAD) , in which chemical attack, salt and water action, and

thermal effects were simulated in one operation;

2. exposure to single causes of stone decay using sulfurous acid fog, sodium

chloride fog, water condensation/evaporation cycling, sodium sulfate penetration

and crystallization, and ultraviolet radiation.

Methods for measuring the effects of the exposures are given together with the test

data; these have been used tc set limits of acceptable performance in preliminary performance criteria for the selection of stone preservatives. The behavior of each stone

preservative tested in meeting these criteria is given. No one stone preservative met

all criteria.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Accelerated laboratory testing; performance criteria; stone decay; stone preservatives.

18. AVAILABILITY IXX Unlimited

~2 For Official Distribution. Do Not Release to NTIS

| y

1 Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CI 3 .Z| /)i Ql{

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