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PUBLICATIONS

Preliminary Performance Criteria for

Stone Treatments for the United

States Capitol

James R. Clifton

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

October 1987

U.S. DEPARTMENT OF COMMERCE

QC

100

U56

87-35^2

1987

NAL BUREAU OF STANDARDS
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Gaithersburg, Marylaad 20899

NBSIR 87-3542 "

PRELIMINARY PERFORMANCE CRITERIA FOR

STONE TREATMENTS FOR THE UNITED

jq

STATES CAPITOL

James R. Clifton

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Gaithersburg, MD 20899

October 1987

U.S. DEPARTMENT OF COMMERCE, Clarence J. Brown, Acting Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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EXECUTIVE SUMMARY

Restoration of the West Central Front of the United States

Capitol began in 1983 after Congress voted money to strengthen,

restore, and preserve that national monument. Restoration

includes cleaning and repainting the stone masonry. Sandstone

from Aquia Creek, Virginia, was used in the original construction.

The sandstone demonstrated rapid decay soon after being put in

place in the late 1700 's. (A large amount of the deteriorated

sandstone damaged in the 1814 fire was replaced between 1816 and

1819.) Paint, which was first applied to the stone surface in

1818, apparently has protected most of the stone from rapid

decay.

Badly deteriorated sandstone is being replaced with Indiana

limestone. During the current restoration work, stone treatments

applied to the cleaned sandstone to extend the lives of both the

stone and subsequently-applied paint has been considered. Stone

treatments, however, have been known to increase or hasten the

damage to stone caused by weathering processes. In view of the

many factors which may affect the performance of treated stone,

the Architect of the Capitol requested the assistance of the

National Bureau of Standards in developing a technical basis to

aid in deciding whether or not treatments should be used on the

stone in the West Central Front. To meet this need the approach

was to develop performance criteria for stone treatment and paint

systems. The pertinent performance criteria could then be used

for screening treatment and paint systems to minimize the

problems caused by their use. It is understood that, for

aesthetic reasons, the Capitol will continue to be painted.

Therefore, any treatment used must become part of a superior

treatment and paint system.

The selection of appropriate performance criteria for a stonetreatment and paint system was based on an analysis of the likely

processes responsible for the deterioration of the sandstone in

the West Central Front. Sandstone deterioration which has taken

place since the first painting does not appear to have been

caused by salt damage or from moisture migrating outward from the

interior of the Capitol. Based on these considerations, it was

concluded that the major deterioration of the stone involved

processes that were associated with water which penetrated into

the stone from its exposed outer surface.

Based on the analysis of the sandstone deterioration, it was

concluded that if a treatment is to be used on the West Central

Front of the Capitol, the treatment or stone-treatment and paint

system should protect the outer surface of the sandstone from

penetration by rain. Since painting the sandstone has effectively

protected it, any stone-treatment and paint system should protect

the stone against water entry for at least as long as the paint

iii
alone would, and preferably much longer. Further, in case all the

deteriorated sandstone has not been removed, a consolidation treatment

must be able to penetrate the deteriorated layers. Based on

these requirements, four performance criteria for treatments were

identified that considered the:

1. effect of treatment on initial paint adhesion,

2. effect of treatment on paint adhesion following prolonged

exposure to moisture,

3. ability of treatment to penetrate deteriorated

sandstone, and

4. ability of treatment to consolidate deteriorated

sandstone.

Because they have not been verified by long-term studies, the

performance criteria proposed in this report are preliminary

criteria.

Five stone-treatments and paint systems were selected for

investigation by a consultant to the Office of the Architect of

the Capitol. The stone treatments consisted of one acrylic

material and four silanes. Their compliance with the critical

performance criteria developed in this study were determined.

Only one of the five treatments appeared to meet all the criteria.

Recommendations are presented regarding the use of stone treatments

on the West Central Front. It is recommended that a treatment be

used on areas of deteriorated sandstone needing consolidation and

on stone located in areas where weathering is most severe.

iv
ABSTRACT

The West Central Front of the United States Capitol is being

restored, including cleaning and repainting the sandstone, and

replacing badly deteriorated sandstone with Indiana limestone.

Application of stone treatments was proposed as a way of extending

the lives of the sandstone and paint. However, without adequate

selection criteria there was no certainty of effective performance

by stone treatments. The purpose of this study was to develop

performance criteria to assist in the selection of stone treatments.

Based on an analysis of expected deterioration processes, it is

concluded that deterioration of the sandstone was most likely

associated with water penetration into the exposed outer surface.

Therefore, if a treatment is to be used, it should protect the

outer surface of the sandstone from rain penetration. In addition,

the treatment should penetrate and consolidate any deteriorated

stone. Also, treatment should not cause premature failure of the

paint. Based on these requirements, four preliminary performance

criteria were developed, but have not been verified by long-term

studies. Of five stone treatments evaluated, one met the four

criteria

It is recommended that treatment be used on areas of deteriorated

sandstone needing consolidation and on stone in areas subjected

to the most severe weathering locations.

Keywords: Consolidation, limestone, paint, performance criteria,

restoration, sandstone. United States Capitol, weathering.

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CONTENTS

1 . INTRODUCTION

1 . 1 Background

1.2 Purpose of Project

1.3 Outline of Report

2. STONE DETERIORATION

2 . 1 Condition of the Sandstone

2 . 2 Causes of Deterioration of Sandstone

3. PERFORMANCE OF STONE TREATMENTS

4. PERFORMANCE REQUIREMENTS

4.1 Performance Requirements for Effect of Treatments

on Stone

4.1.1 Moisture Accumulation

4.1.2 Resistance to Internal Expansive Forces

4.1.3 Consolidation Ability

4.1.4 Penetration of Weathered Stone

4.1.5 Durability

4.2 Performance Requirements for Effect of Treatments

on Paint

4.2.1 Bond Development

4.2.2 Bond Degradation

5. TEST MATERIALS

5.1 Stone

5 . 2 Stone Treatments and Paints

6. TEST METHODS AND RESULTS

6.1 Water Absorption

6.1.1 Test Method

6.1.2 Results and Discussion

6.2 Water Vapor Transmission

6.2.1

Test Method

6.2.2 Results and Discussion

6.3 Sodium Sulfate Crystallization Test

6.3.1 Test Method

6.3.2 Results and Discussion

6.4 Consolidation Ability

6.4.1 Test Method

6.4.2 Results and Discussion

6 . 5 Penetration Depth

6.5.1 Laboratory Test

6.5.2 Field Test

6.6 Combination of Deterioration Processes

6.6.1 Test Method

6.6.2 Results and Discussion

6.7 Adhesion between Paint and Stone

6.7.1 Test Method

6.7.2 Results and Discussion

6.8 Resistance of Paint to Moisture Condensation

vii
6.8.1 Test Method

6.8.2 Test Results

7. PRELIMINARY PERFORMANCE CRITERIA

7.1 Performance Criteria

7.1.1 Paint Adhesion

7.1.2 Resistance of Paint to Moisture

7.1.3 Consolidation of Weathered Stone

7.1.4 Penetration Depth

7.2 Compliance with Proposed Performance Criteria

8. SUMMARY AND RECOMMENDATIONS

8 . 1 Summary

8 . 2 Recommendations

9. ACKNOWLEDGEMENT

10. REFERENCES

APPENDIX A. Tables of Experimental Data

LIST OF FIGURES

1. Schematic of Localized and More Uniform Stone

Deterioration Processes.

2 . Accelerated Weathering Apparatus

LIST OF TABLES

1. Compliance of Treatments, When Applied to Sandstone, with

Proposed Performance Criteria

viii
1 . INTRODUCTION

1 . 1 Background

Restoration of the West Central Front of the United States Capitol

began in 1983, the stone has been cleaned, and some stone has been

replaced. The walls are to be repainted. This section of the

Capitol was constructed in the late 18th and early 19th centuries

using a sandstone from Aquia Creek, Virginia, which rapidly

deteriorated. B.H. Latrobe observed (1) that it "..cracks and

falls to pieces on exposure to air and sun. Sometimes, contrary

to all expectations and appearance, the frost tears it to pieces.

All of it expands when wet, and contracts when dry." Fire damaged

stone was replaced between 1815 and 1819. In 1818 the stone walls

were first painted to protect them from the weather. During the

present restoration, an inspection of the stone revealed that

deterioration was confined largely to the surface of the stone.

Because of cracking combined with surface deterioration, approximately

30 percent of the sandstone had to be replaced with Indiana

limestone. Over the years about 35 layers of paint had been

applied to the sandstone; the paint never was thoroughly removed

until the present restoration. The color of the repainted West

Central Front will closely match those of the other natural

marble walls of the Capitol.

Application of stone treatments to extend the lives of both the

sandstone and paint had been suggested at the start of the

current restoration. Materials most often used to treat stone

are intended to serve as preservatives and consolidants . The

materials, however, have been known to accelerate the deterioration

of stone (2)In recent reviews of stone preservatives and

consolidants (3,4), it was noted that some preservatives and

consolidants increased the harm to stone caused by weathering

processes. Because the Capitol will continue to be painted, any

treatment used must become a part of a superior treatment and

paint system.

1.2 Purpose of Project

The Architect of the Capitol asked National Bureau of Standards

(NBS) to develop technical criteria to help decide whether or not

treatments should be used on the stone on the West Central Front

of the Capitol. The approach taken was to develop performance

criteria for stone treatments. The benefits are that performance

criteria describe what the stone treatments should accomplish and

define how their performance might be measured. Treatments

meeting the pertinent performance criteria could then be considered

for use.

1
During the project, the Architect of the Capitol requested that

the project's scope be enlarged to include evaluation of the

performance of stone-treatment and paint systems. Thus, performance

criteria were also developed for these systems.

The performance criteria proposed in this report are considered

to be preliminary since they have not been verified by long-term

field studies.

1.3 Outline of Report

In Section 2, possible deterioration processes of the stone in

the West Central Front are discussed. Analysis of possible

deterioration processes is important in developing performance

criteria for stone treatments. Section 3 reviews performances of

stone treatments. Section 4 discusses performance requirements

for stone treatments. Section 5 identifies materials used in the

study. Section 6 describes test methods and test results.

Section 7 describes preliminary performance criteria for treatments.

Information on the compliance of candidate treatments with the

performance criteria is also presented. Recommendations on the

use of treatments on the Capitol are given in Section 8. Tables

of the test data are in Appendix A.

2. STONE DETERIORATION

2 . 1 Condition of the Sandstone

According to Latrobe's report (1), the sandstone in the West

Central Front of the US Capitol demonstrated rapid decay soon

after being put into place in the late 1700 's and early 1800's.

Paint first applied to the stone surface in 1818, has apparently

protected most of the stone from further rapid deterioration.

Some 35 layers of previously applied paint were only thoroughly

removed in the present restoration program. Undoubtedly the

previous paints, mostly oil-based, formed a barrier of low

permeability to the passage of moisture into or out of the stone.

The depth of stone deterioration observed after paint removal was

found in most areas to range up to 0.5 in (13 mm). In a few

areas, where the exposure conditions were the most severe and

carved stone was used (e.g., cornices) it was as deep as 1 in (25

mm) . In most cases, the severity of the deterioration appears to

be random over the surface of the walls and not associated with

specific locations except where exposure conditions were the most

extreme. During a scanning electron microscopy study no soluble

salts were detected in the stone pores. However, had salts been

present, they might have been removed during the paint removal.

Veins of feldspar are present in the sandstone. During tests on

the effect of treatments on moisture transport, surface staining

of test specimens occurred.

2
Regarding the cause of stone deterioration, the sandstone was

found by x-ray powder diffraction to be siliceous and thus should

not be readily attacked by acid precipitation. The rate of

deterioration since the stone was painted has been low, with a

maximum loss of about 1 in (25 mm) of stone over some 170 years.

Some of the observed deterioration may have taken place before

the stone was painted. Records do not reveal how much stone was

replaced between 1815 and 1819.

2.2 Causes of Sandstone Deterioration

Based on the present condition of the sandstone, the low rate of

deterioration since the first painting, and the written record

before 1818, it is concluded that the major deterioration of the

stone in the West Central Front of the Capitol involved processes

associated with water penetration into the stone's exposed outer

surface. The justification for this conclusion is as follows: If

salt damage occurred, it would not likely be random but would

usually be concentrated near the source of the salt; for example,

at the base of the wall if the source was ground water (fig. 1)

Also, oil-based paint could aggravate the problem by trapping

salts in the stone. Similarly, if moisture was migrating to the

stone surface from the interior of the Capitol, freezing and

thawing damage would be aggravated by the paint because it would

reduce the rate of water evaporation; also, the resulting

deterioration would not likely be random but would be concentrated

near interior sources of moisture or at locations where thermal

gradients would drive the moisture to cooler regions of the stone

(fig. 1) . However, the paint has effectively protected the

sandstone from the rapid deterioration evidenced at the time when

the stone was unpainted.

3
Moisture accumulation

T| : Inside temperature

Tq: Outside temperature

RH| : Inside relative humidity

RHq: Outside relative humidity

If To<32*F this sector may be susceptible to freezing and thawing

damage

Moisture accumulation

Moisture movement

Damage by saltsGround water

laden with saltsRoof

Source of moisture,

e.g., kitchen

If: T,>To and RH|>RHo

Then: Moisture

- movement outwards

Floor

If: To>T| and RHo>RH,,

Then: Moisture

movement Inwards

Possible result: Peeling paint

Basement

Precipitation

-Damage caused by

precipitation likely to be of general uniformity on stone vertical surfaces. More severe damage likely on curved and horizontal surfaces

Damage from deicing salts

Walkway

Figure 1. Schematic Showing Factors affecting Stone Deterioration

Processes

4
3. PERFORMANCE OF STONE TREATMENT

Because the presence of moisture is associated with many of the

common stone deterioration processes, "waterproofing" or "water

repellent" materials have been applied to stone masonry for many

years in an effort to reduce the rates of deterioration (3)In

many instances, the use of these materials has been found to

result in more stone damage than would normally occur by natural

weathering processes. In some cases, their poor performance

often has been attributed (4) to the formation of a thin layer of

the material that is relatively impervious to liquid water but

not to water vapor. This layer permitted the evaporation of

aqueous salt solutions, rising from the ground by capillary

action, to leave deposits of salts behind the surface of treated

stone. Some waterproofing materials have been applied in such

amounts that the pores of stone, at least those close to the

surface, are filled. This impedes the passage of both liquid

water and water vapor, thereby increasing the probability of

freezing and thawing damage occurring under conditions in which

moisture condenses behind the surface treatment. Moisture also

could accumulate at the interface of a treated stone surface and

a paint film thus, possibly reducing the adhesion of paint.

Paints themselves can perform as waterproofers. Since paint is

unlikely to penetrate deeply into the stone, any resulting damage

associated with the accumulation of moisture probably would be

near the surface of the stone.

Consolidants are treatments intended to re-establish cohesion of

the particles of deteriorated stone (4)

Experience with

consolidants has shown that their ability to penetrate weathered

stone is one of the main factors controlling their performance

(5,6). Superficially-penetrating consolidants tend to fill the

pores of stone surface layers, thereby reducing their permeability

and causing problems similar to those described for waterproofing

materials (4)

Because the performance of stone treatments often has not been

satisfactory, stone treatments and application methods should be

evaluated by laboratory or field tests which can simulate the

conditions encountered in service, before they are used on actual

structures. Both standard test methods and performance criteria

need to be developed to form a basis for evaluating and selecting

stone treatments.

5
4. PERFORMANCE REQUIREMENTS

Performance requirements for a material are general qualitative

statements describing the performance expected of that material

for fulfilling an intended purpose. Based on the requirements,

tests may be selected to measure desired performance characteristics.

Then, performance criteria may be developed from the test results,

past experience, and from other relevant information. In this

section, performance requirements for stone treatments are

proposed as a basis for the selection of test methods. They were

developed in collaboration with the Office of the Architect of

the Capitol. The applicability of a particular requirement may

depend on specific exposure conditions. Therefore some of the

following requirements may not be critical for the West Central

Front based on the analysis of the apparent major deterioration

processes (Section 2.2). They are presented as requirements

always to be considered in selecting stone treatments or paints.

The requirements below are not necessarily all-inclusive and others

may need to be specified depending on the exposure conditions.

The following two performance requirements should be met when stone

treatments are used as preservatives: a) the treatment should

increase the service life of the stone; and b) where paint is

applied, the treatment should not reduce the performance of the

paint compared to paint applied to untreated stone. These

essential broad considerations were subdivided into more specific

categories for consideration in the study. The necessity of

fulfilling specific requirements depends upon the likely causes

of the deterioration of the specific stone in question.

4.1 Performance Requirements for Effect of Treatments on Stone.

Treatments should increase the service life of the stone. Test

methods which are recommended to determine compliance are

mentioned.

4.1.1 Moisture Accumulation. A stone treatment should not permit

accumulation of moisture in the stone sufficient to cause

moisture-related deterioration (e.g., from freezing and thawing).

The effect of treatments on the accumulation of moisture in stone

was investigated by measuring water absorption (Section 6.1) and

water vapor transmission (Section 6.2) of treated and untreated

stone specimens. Also measured was the water vapor transmission

of stone-treatment and paint systems.

4.1.2 Resistance to Internal Expansive Forces. A stone treatment

should increase the resistance to damage by internal expansive

forces resulting from such processes as salt crystallization,

freezing and thawing. However, some treatments have decreased

the resistance of stone to such processes, thereby substantially

increasing the severity of the processes (4)

.

The resistance of

6
treated stone to salt crystallization damage was investigated by

the sodium sulfate crystallization test (Section 6.3). The

freezing and thawing resistance was investigated in an accelerated

test which combines several deterioration processes (Section

6 . 6 ).

4.1.3 Consolidating Ability. A stone treatment used as a

consol idant should strengthen deteriorated surface layers of

stone. The consolidating abilities of treatments were determined

by measuring the compressive strengths of treated and untreated

stone specimens (Section 6.4).

4.1.4 Penetration of Weathered Stone. A stone consolidant

treatment should be able to penetrate, to a reasonable depth,

weathered layers of stone. If the stone is deeply weathered then

it would probably be replaced. The depth of penetration of

treatments was measured in both laboratory and field studies

(Section 6.5).

4.1.5 Durability. A stone treatment should withstand the service

environment to which it is exposed for a sufficient time to be

useful. The resistance to weathering of stone treatments was

investigated by an accelerated test (Section 6.6).

4.2 Performance Requirements for Effect of Treatments on Paint.

In general , stone treatments should not accelerate failure of

paint by any process. In the present study, the main concern was

the effect of the treatment on the adhesion of the paint and on

the effect of sustained exposure to moisture on paint adhesion.

4.2.1 Bond Development. Few if any studies have been carried out

to establish acceptable levels of bond development between paints

and stone. Because of the lack of bond criteria, it was decided

to require that the strength of the bond developed between the

stone treatment and stone should not be substantially less than

the bond developed between the stone and paint. Bond was

measured by using a pull-off adhesion tester (Section 6.7).

4.2.2 Bond Degradation. Bond between treatment and paint should

not be degraded by moisture at a rate faster than the paint/stone

bond. Effect of moisture on bond strength was determined by

water condensation testing (6.8).

7
5. TEST MATERIALS

5.1 Stone

Sandstone specimens were taken from stone blocks removed from the

Capitol and cut to size by NBS. The mineralogy of the sandstone

was determined by x-ray powder diffraction and was found to

consist predominantly of quartz with veins of feldspar.

Specimens of Indiana limestone were taken from stone blocks

procured for replacement of deteriorated sandstone.

5 . 2 Stone Treatments and Paints

Stone treatments were selected for investigation by the Architect

of the Capitol and his consultants. Altogether, five materials

were selected for evaluation (Table Al) ; one acrylic (A) and four

silanes (SI, S2, S3 and S4)

.

Treatments S2, S3, and S4 were all

from the same supplier. Generally, treatments were applied to

stone specimens by the suppliers, since any large scale application

on the Capitol would be in accordance with a supplier's instructions.

Suppliers were requested to use application methods that would

give specimens representative of field treated stones. In the

case of the silanes, NBS also prepared some treated stone

specimens, following the application instructions of the suppliers.

Paints (Table A2) were those recommended by the suppliers of the

stone treatments for their compatibility with the treatments.

Each paint is identified by the same code as the treatment with

which it is to be used. NBS was provided with samples of paints

and performed tests to identify possible application problems.

All paints were easily applied with a brush and no unacceptable

flow or curing characteristics were observed. Paint from the

acrylic treatment supplier was acrylic-based, and paints from

the silane suppliers were latex.

6. TEST METHODS AND RESULTS

Tests used to investigate the performances and characteristics of

stone treatments and paints are described in this section. If an

ASTM (American Society for Testing and Materials) standard test

method was available, it was selected over other tests to

facilitate the testing process. Also, the use of a standard test

helps to indicate testing conditions and procedures. Whenever

possible, data were obtained using specimens prepared by

suppliers of the stone-treatment and paint systems.

8
6.1 Water Absorption

6.1.1 Test Method. The water absorptions of treated and untreated

stone specimens were measured using 2 in (51 mm) cubes following

the methods of ASTM C 97 (7) . Water absorption values

were calculated as mass gained during water immersion relative

to the dry mass of the specimens. Then ratios of water

absorptions of treated specimens to untreated specimens were

calculated and expressed as percentages.

6.1.2 Results and Discussion. Water absorption values for

treated stone specimens and untreated stone specimens are given

in Table A3. All treatments were effective in reducing water

absorption of both sandstone and limestone specimens. In comparing

treatments, the silanes (treatments SI, S2, S3, and S4) were more

effective in reducing water absorption of the sandstone (reduction

to 4.3 to 8.6 percent) than the acrylic (treatment A, reduction

to 53 percent) . With limestone, results with the acrylic

(reduction to 11.9 percent) were in the same range as with the

silanes (reduction to 18.4 percent). Low water absorption could

be important if the absorption of water (e.g., from rainwater)

results in the manifestation of a deterioration process, e.g.,

freezing and thawing damage.

6.2

Water Vapor Transmission

6.2.1 Test Method. Water vapor transmissions (WVT) of treated

stone, with and without a paint film, and of untreated stone were

measured following the methods of ASTM E 96 (8) . Test specimens

with a diameter of 3 in (76 mm) and thickness of 0.25 in (6.4 mm)

were used. The tests were carried out in a closed cabinet at a

relative humidity of 88 percent and temperature of 90 *F (32»C)

for 8 days. Values were calculated as the percentage of mass of

water vapor passing through treated stone specimens into the

desiccant with respect to the water vapor moving through untreated

specimens

6.2.2 Results and Discussion. Results of the WVT studies are

presented in Table A4 for specimens with treatments and paint

films. Some trends are apparent in the data: treatments reduced

the WVT's of limestone more than the WVT's of sandstone; painted

and treated sandstone specimens had higher WVT's than corresponding

limestone specimens. In a few cases WVT's higher than 1.0 were

obtained with treated sandstone which are considered to be

statistically insignificant. Under certain conditions, a low WVT

can be harmful, because it can result in the accumulation of

water behind the surface of the treated stone. If significant

amounts of moisture in the form of vapor is entering untreated

stone through its outer surface, a low WVT could be desirable.

9
6.3 Sodium Sulfate Crystallization Test

Resistance of stone to internal stresses, such as those produced

by salt crystallization and freezing and thawing of water, can be

tested by following procedures of ASTM Method C 88 (9) . The test

consists of immersing stone in saturated solutions of sodium

sulfate, followed by oven drying, and repeating the process until

the stone fails. Oven drying results in precipitation and

dehydration of the salt in pores. Internal expansive stresses are

produced by rehydration of sodium sulfate during repeated

immersions and precipitation during drying. If tensile strength

of stone is exceeded by expansive stresses produced by precipitation

and rehydration of sodium sulfate, stone begins to crack. The

failure mechanism intrinsic to this test may not be the same as

that actually occurring in the field, however a more appropriate

ASTM standard test method has not been developed.

6.3.1 Test Method. The methods given in ASTM C 88 (9) were

followed. Failure was defined as spalling occurring on all sides.

Often spalling was accompanied by a sudden loss of mass. In some

tests, however, gain in mass by precipitated sodium sulfate

exceeded the mass loss by spalling. Therefore, a specimen could

be badly spalled but have only a modest mass change; thus a

visual failure criterion was used.

6.3.2 Results and Discussion. Results of the sodium sulfate

test (Table A5) indicate that treated stone specimens had higher

resistances to the effects of the precipitation and rehydration

of the salt than untreated stone. Treatments S3 and S4 were the

most effective in improving the resistance of stone to sodium

sulfate attack. For example, resistance of sandstone was increased

from 7 to 13 cycles when treated with S3 and S4, and the resistance

of limestone was increased from 4 to 10 cycles.

6.4. Consolidation Ability

The consolidation abilities of treatments were evaluated by

measuring the compressive strengths of treated sandstone and

limestone specimens.

6.4.1 Test Method. The compressive strength of 2 in (51 mm)

cubes of treated and untreated sandstone and limestone were

measured in accordance with ASTM C 170 (10) . 6.4.2 Results and Discussion. Results of testing specimens

prepared by suppliers of the treatments (Table A6) indicate that

the treatments had varying effects on the compressive strength of

sandstone. Apparent decreases occurred with treatments SI, S2,

and S4. There was essentially no change with treatment A, and an

increase of 16 percent with treatment S3 . All the treatments

increased the compressive strength of limestone, ranging from 9

percent with treatment SI to 27 percent with treatment S2.

10
Only one sandstone specimen with treatment SI was furnished by

the supplier for compressive strength determination. Because of

its low compressive strength (4400 psi (30.3 MPa)), further tests

were performed. Three additional sandstone specimens using

treatment SI were prepared by NBS investigators. Treatment was

applied using a paint brush until the surfaces were saturated.

Average compressive strength of these specimens was 5,660 psi

(39.0 MPa). The reason for low compressive strength of the

specimen prepared by the supplier is not known, but possibly

could be caused by a defect in the stone itself or by improper

curing of the treatment. In a further investigation of the effect

of application method on strength development, three sandstone

specimens were immersed in treatment SI for 10 minutes, allowed

to cure for 4 days at 22 *C, and tested in compression. The

average compressive strength for these specimens was 8050 psi

(55.5 MPa). These results indicate that strengths of treated

stones are dependent on the depths of penetration of the treatments.

6.5 Depth of Penetration

6.5.1 Laboratory Test

Depths of penetration of treatments in 2 in (51 mm) sandstone

cubes, fractured in compressive strength determinations, were

measured. These specimens had been prepared by the treatment

suppliers. Depth of penetration was estimated by treating

surfaces with water and visually observing where water ceased to

form droplets and started to penetrate fractured surfaces. Also,

concentrated sulfuric acid was applied and the darkening (usually

slight) of surfaces, denoting the presence of organic materials,

was observed. Both methods gave similar values. The depths of

penetration of treatments in sandstone specimens prepared by

suppliers are given in Table A7. Depths ranged from 0.3 in (8

mm) to 1 in (25 mm) . Penetration depended upon the method of

application. For example, when applied in thin films with a

brush by the supplier, treatment SI penetrated to a depth of

around 0.3 in (8 mm). However, when sandstone specimens were

immersed by NBS investigators, in the silane for approximately

10 minutes, it penetrated to the center of the cube. When the

silanes S2, S3, and S4 were applied by dipping sandstone specimens

in them for 5 minutes, they penetrated nearly to the center of

the cube (0.8 in (20 mm)). These treatments also penetrated to

the center of 2 in (51 mm) cubes when sandstone specimens were

immersed for approximately 10 minutes. Treatment A, which was

injected under pressure by the supplier using proprietary

equipment, was found to be present in the center of 2 in (51 mm)

cubes

11
6.5.2 Field Test. Treatments A, SI, and S4 were applied to both

sandstone and limestone blocks located in the West Central Front

Wall of the US Capitol. Treatments A and S4 were applied by their

suppliers. The supplier of treatments S2, S3 and S4 regarded the

penetration ability of S4 to be representative of the abilities

of treatments S2 and S3. This assumption appeared to be reasonable

because the three treatments are based on the same silicic ethyl

ester with only small amounts of different additives to give

desired performances. Further, they all gave essentially the same

depth of penetration in the laboratory study. Recent field

studies by the Architect of the Capitol's staff confirmed that S3

has the same penetration ability as S4. Treatment SI was applied

by NBS at the request of the supplier, closely adhering to the

supplier's application guidelines. After the treatments had

cured for the time specified by the suppliers, cores of 2 in (51

mm) diameter and 4 in (100 mm) length were removed from treated

sections by a contractor. Depths of penetrations were measured

by visually observing the location where water droplets ceased to

form on the specimen's surfaces.

Test results are given in Table A8 . Depths of penetration

measured within 48 hours of application ranged from 0.7 in (18

mm) to 3.5 in (89 mm) in sandstone, and from 0.6 in (15 mm) to

3.1 in (79 mm) in limestone. Another set of cores were taken 30

days after application. In the case of sandstone, the penetration

depths after 30 days of curing were all 1.0 in (25 mm) or

greater, and had increased between 20 to 80 percent compared to

initial measurements. Similar increases in depths of penetration

of limestone after 30 days of curing were less than 11 percent.

Depth of penetration depended on the application method in the

order: pressure injection > spraying > brush application.

6.6 Combination of Deterioration Processes

A test was developed to attempt to obtain evidence of

detrimental effects of a combination of the following weathering

processes: rapid temperature changes, wetting and drying,

freezing and thawing, and aqueous dissolution. Independently,

these processes may only cause slow rates of deterioration. When

combined, the processes could have synergistic effects, thereby

significantly increasing the rate of deterioration. Such an

accelerated test with a single fixed cycle, however, would not

permit isolation of the effects of individual processes.

6.6.1 Test Method. By using the apparatus illustrated in fig. 2,

treated and untreated stone were exposed to accelerated weathering

conditions and the combined effects of temperature cycles, wetting

and drying, and freezing and thawing, on the performances of the

treatments were investigated. Stone specimen blocks, with

dimensions of 1.0 x 1.0 x 0.38 in (25 x 25 x 10mm) were subjected

to cycles consisting of the following, in sequence: (1) heating

12
at 104 *F (40 *C) for 15 minutes by a 1200 watt electric heater

with a fan providing an air flow rating of 75 cu ft/min; (2) 3

minutes immersion in water at 72*F (22*C); (3) cooling at 4*F

(-15*C) for 30 minutes; (4) drying by warm air as specimens leave

the freezing chamber and enter the warm air chamber. A cycle

required 70 minutes to complete, thus specimens were subjected to

approximately 21 cycles in a 24-hour period. After testing,

surfaces and interiors of specimens were examined visually and

with an optical microscope at a magnification of 10 to determine

if cracking had taken place or if there were any other sign of

deterioration

Conditions used in the accelerated test were selected based on

analysis of weather conditions to which stone treatments would be

subjected if applied to stone in the West Central Front. For

example, the maximum temperature of 104 *F (40 *C) and minimum

temperature of 4*F (-15 *C) bracket the average monthly temperature

in the Washington D.C. area, which ranges from around 30 *F (-1*C)

in January to around 80*F (27*C) in July (11).

Specimens were subjected to a total of 1660 test cycles which

consisted of several runs of variable test cycles because

specimens were added to the set of test specimens as they were

received from their suppliers. The total number of cycles was

established based on the need to complete the project within a

specified time.

6.6.2 Results and Discussion. Treated and untreated sandstone

and limestone specimens were subjected to 1660 cycles. No

evidence of cracking deterioration was observed (Table A8)

Some

brownish surface staining on the surfaces of the specimens was

observed.

Simulation of actual weather conditions by an accelerated test is

difficult because short term fluctuations are often hidden in

weather data. Also, the rate that conditions change is difficult

to model. Correlation of 1660 cycles to actual weathering,

therefore, can only be qualitative as follows. In an average

winter in the Washington D.C. area, some 45 freeze-thaw cycles

occur (11) , thus 1660 cycles roughly corresponds to 37 "average

years" relative to the number of freeze-thaw cycles. Maximum

temperature exceeds 90 *F (32*C) for an average of 30 days per

year in the Washington D.C. area (11) . Therefore, 1660 test

cycles corresponds to 55 "average years" relative to the number

of days per year exceeding 90 *F (32*C)

Such correlations,

however, should not be taken to indicate an actual correspondence

between test cycles and weathering conditions. Nevertheless, the

test results do not suggest that the treated stone would be less

durable than the untreated stone under temperature cycling or

wetting and drying.

13
6.7 Adhesion between Paint and Stone

6.7.1 Test Method. The adhesion between paints and specimens of

treated and untreated stone were measured following the method

given in ASTM D 4541 (12) . This method uses a pull-off adhesion

tester. Briefly, a metal disk is secured to the coating surface

with an epoxy. A testing apparatus is attached to the

button and force applied perpendicular to the surface of the

coating. The force is gradually increased until the coating

material is detached or some other form of failure occurs. The

test apparatus and method are described in more detail in

Reference 13.

6.7.2 Results and Discussion. Test results are presented in Table

AlO. Data indicate that treatments can have a significant effect

on the paint bond. For example, bond strength of paint applied

over treatment SI is substantially less than that applied to

untreated stone. Also, the mode of failure is changed to an

adhesive failure between the paint and treatment on treated. stone

from a cohesive failure of paint on the untreated stone. In the

case of the paint applied over treatments S2, S3, and S4, the

bond strengths were highest for the treated stones. Paint

applied over treatment A exhibited failure in the paint film for

both stone types.

6.8 Resistance of Paint to Moisture Condensation. Several

accelerated test methods are available to study the effect of

moisture on painted specimens. A major concern relative to the

use of treatments on the Capitol is that moisture will accumulate

at the interface between treated stone and paint resulting in

loss of paint adhesion. The water vapor condensation test is a

severe test (14) of the effect of moisture on the bond between

paint and substrate and the tendency to blister.

6.8.1 Test Method. The apparatus and procedures described in ASTM

Method D 2247 (15) were used. The apparatus provides water at a

constant temperature as a source of vapor. Test panels are placed

over the water vapor. The panels are at a lower temperature than

the water resulting in condensation on the underside of the

panels. Water temperature was set at 110*F (43*C). The panels

were subjected to condensing moisture for 18 hours followed by

drying for 6 hours to promote the formation of blisters.

Specimens were panels of nominal face size 6.75 in (171 mm) by

2.75 in (70 mm), and were 0.25 in (0.64 mm) thick. Paint films

were applied to one face of each panel. Both painted and

unpainted faces were exposed to water vapor. Triplicate specimens

of each treatment-paint combination were tested for 28 days.

14
Figure 2. Accelerated Weathering Apparatus.

15
6.8.2 Test Results. Test results are given in Table All. After

40 days of testing, no evidence of paint blistering was observed.

Brown stains appeared on the outer sides of stone panels within

the first week of testing. Similar stains were not observed with

limestone specimens. The paint submitted by the supplier of stone

treatment SI became soft and could easily be removed with a

spatula. There were no obvious changes in the hardness of the

other paints.

7. PERFORMANCE CRITERIA

The selection of appropriate performance criteria for a stonetreatment and paint system should be based on an analysis of

likely exposure and service conditions. Then these performance

criteria will form a set of criteria which a treatment should be

required to meet. The performance criteria proposed in this

report are considered to be preliminary criteria as they have not

been verified by long-term field studies.

7.1 Performance Criteria

Based on the analysis of sandstone deterioration given in Section

2, it is concluded that if a treatment is to be used on the West

Central Front of the United States Capitol, the treatment or stonetreatment-and-paint system should protect the outer surface of

the sandstone from penetration by rainwater. Since painting the

sandstone has effectively protected it, a treatment should not

cause premature paint failure (i.e., failure earlier than that

occurring when paint is protecting untreated stone) . Since all

deteriorated stone may not been removed, a treatment should

consolidate the sandstone by penetrating "to the depth of

deterioration.

Performance requirements and criteria for stone treatment and

paint systems considered for use on the West Central Front of the

Capitol are given below.

7.1.1 Paint Adhesion. The adhesion between the treated stone and

the paint should be adequate for sustained acceptable performance.

In the absence of other information, initial adhesion should not

be less than the adhesion between the paint and untreated stone.

Otherwise premature failure of the paint may occur. If a

cohesive failure occurs in the stone's surface, then strength of

the treated stone is the limiting factor, not the strength of the

paint-stone bond. Therefore, a cohesive failure is considered to

indicate that the paint adhesion to treated stone is acceptable.

Adhesion was measured as described in Section 6.5 and test

results are given in Table AlO.

16
7.1.2 Resistance of Paint to Moisture. Adhesion between the paint

and the treated stone should not be degraded by moisture at a

rate faster than the adhesion between paint and untreated stone.

Effects of treatments on paint adhesion were evaluated by

exposing for 40 days test specimens of painted stone to condensing

moisture. To meet the requirement, the amount of visible loss of

adhesion, such as blistering, occurring between paint and treated

stone should not be more than that occurring between paint and

untreated stone when the testing is carried out as described in

Section 6.8. The test results are given in Table All.

7.1.3 Consolidation of Weathered Stone. Stone treatment should

consolidate surface deteriorated stone. Gauri recommended (17)

that the compressive strength of treated weathered stone should

be at least 10 percent above that of untreated and unweathered

stone. Because of the subjectivity in deciding what constitutes

weathered stone, a 10 percent increase in compressive strength of

treated stone above that of untreated and unweathered stone was

selected as the criterion. The results with sandstone are used in

determining compliance with the criterion. The purpose of using

a consol idant would be to treat weathered stone, and the nonweathered

limestone was only recently put in place. The compressive strength

of stone was measured as described in Section 6.5 and test

results are given in Table A6.

7.1.4 Depth of Penetration. Stone treatment should be able to

penetrate beyond the depth of deteriorated stone. Based on a

visually observable maximum depth of deterioration, except in a

few cases where exposure conditions were most severe, of 0.5 in (13

mm) , a required depth of 1 in (25 mm) after 32 days was selected.

This required depth of penetration should help to ensure that

deteriorated stone is bonded to sound (unweathered) stone.

Sandstone that had deteriorated to a depth greater than 1 in (25

mm) was replaced with Indiana limestone. The results of the

field tests on sandstone (Section 6.5.2) were used in determining

if treatments complied with the criterion. Test results are given

in Table A8

.

7.2 Compliance with the Preliminary Critical Performance Criteria

The extent of compliances of the treatments, applied to the

sandstone, with preliminary critical performance criteria are

given in Table 1. Treatments S2 and S3 were not included in the

field test as their supplier elected to apply only S4. Results

of the laboratory study on depth of penetration (see Table A7)

indicate that the penetrating abilities of S2 and S3 are similar

to that of S4. Therefore, S3 appears to meet the criterion for

depth of penetration, in addition to the other criteria.

17
Table 1. Compliance of Treatments, When Applied to Sandstone,

with Proposed Performance Criteria

Proposed Performance

Criteria

Paint Adhesion

Resistance of Paint

to Moisture Exposure

Consolidation

Depth of Penetration

(based on field testing

after 32 days)

Treatment Designation^

A

pb

C

F

C

C

SI

F

C

F

F

C

S2

CC

C

F

Cd

Cd

S3

C

C

C

C

C

S4

C

C

F

^Where appropriate, includes paint-treatment system.

^F indicates failure to comply with the criterion.

^C indicates compliance with the criterion.

djndirect evidence of compliance as treatment not included in

field test. However, laboratory results indicate that the

depth of penetration of S2 is similar to S3 and S4.

18

n

o
8. SUMMARY AND RECOMMENDATIONS

8 . 1 Summary

The main purpose of this project was to develop a technical basis

to aid in deciding if treatments should be used on the stone in

the West Central Front of the U.S. Capitol. The approach taken

to meet this need was to develop performance criteria for stone

treatments based on analysis of the most probable processes

responsible for the deterioration of sandstone in the West

Central Front of the Capitol. The main processes responsible for

the deterioration of the sandstone appear to be associated with

exposure of the outer surface to precipitation. There is no

evidence that moisture migration from the interior of the Capitol

to the outer surfaces of the sandstone has caused water-related

deterioration. Also, rising ground water leading to the deposition

of soluble salts does not appear to have been a problem.

Four critical performance criteria were identified: 1) the effect

of treatments on the performance of paint, 2) the ability of

treatments to consolidate deteriorated sandstone, 3) the ability

of treatments to penetrate and 4) the consolidation of the layers

of weathered sandstone. The performance criteria are considered

preliminary because they have not been verified by long-term

field exposure testing. Therefore, compliance with the criteria

does not unequivocally ensure that treatments will perform as

intended. However, on the basis of current knowledge, it is

expected that treatments that meet the criteria will perform

satisfactorily.

8.2 Recommendations

In developing recommendations regarding the use of stone treatments,

specific needs for them were analyzed as follows: Painting the

sandstone has been an effective approach to reducing the extent

of deterioration and for aesthetic reasons both sandstone and

replacement limestone will be painted. Also, most of the severely

deteriorated sandstone has been replaced with Indiana limestone.

Therefore, it does not appear to be necessary to treat all the

sandstone in the West Central Front. However, the use of consolidants

could be of significant benefit if deteriorated layers are still

present on some sandstone. Another reason to use a treatment

would be to protect areas which are most likely to be subjected

to severe weathering, such as cornices and tops of parapet walls.

Therefore, it is recommended that treatment S3 be used on the

West Central Front on areas of deteriorated sandstone needing

consolidation and on stone located in areas subjected to the most

severe weathering. No evidence was found that the application of

stone treatments to newly placed limestone would be detrimental.

Therefore the treatment could be applied to selected regions of

the West Central Front or to the complete stone masonry.

19
9. ACKNOWLEDGEMENTS

The author wishes to acknowledge the helpful suggestions by

Dr. Geoffrey Frohnsdorff and Mr. James Gross, National Bureau of

Standards, and Mr. William Ensign and his colleagues and consultants.

Office of the Architect of the Capitol, which contributed

significantly to the project and the preparation of this report.

20
9. REFERENCES

1. Letter in files of Architect of the Capitol.

2. W. H. Dukes, "Conservation of Stone: Chemical Treatments," The

Architects' Journal Information Library, pp. 433-438 (August

23, 1972).

3. G. A. Sleater, "A Review of Natural Stone Preservatives,"

NBSIR 74-444, National Bureau of Standards, Gaithersburg, MD,

(1973) .

4. J. R. Clifton, "Stone Consolidating Materials - A Status

Report," NBS Technical Note 1118, National Bureau of

Standards, Gaithersburg, MD, (1980)

.

5. W. H. Gutt, "Conservation of Stone. The Next Steps," Stone

Industries, London, (May-June 1973)

.

6. L. Arnold, D. B. Honeyborne, and C. A. Price, "Conservation of

Natural Stone," Chemistry and Industry, pp. 345-347 (April 17,

1976)

.

7. "Standard Test Method for Absorption and Bulk Specific Gravity

of Natural Building Stone," ASTM Designation C 97.

8. "Standard Test Methods for Water Vapor Transmission of

Materials," ASTM Designation E 96.

9. "Standard Test Method for Soundness of Aggregates by Use of

Sodium Sulfate or Magnesium Sulfate," ASTM Designation C 88.

10. "Standard Test Method for Compressive Strength of Natural

Building Stone," ASTM Designation C 170.

11. K. A. Gutschick and J. R. Clifton, "Durability Study of 14-

Year Old Masonry Wallettes," Masonry Past and Present, ASTM

STP 589, American Society for Testing and Materials, pp. 76-

95 (1973).

12. "Standard Method for Pull-Off Strength of Coatings using

Portable Adhesion Testers," ASTM Designation D 4541.

13. J. F. Seiler, M. E. McKnight, and L. W. Masters , "Development

of A Test Apparatus and Method for Measuring Adhesion of

Protective Coatings," NBSIR 82-2535, National Bureau of

Standard, Gaithersburg, MD, (1982)

.

14. "Paint Testing Panel," ASTM STP 500, 13th Edition (1972).

15. "Standard Test Method for Testing Coated Metal Specimens at

100% Relative Humidity," ASTM Designation D 2247.

21
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V
APPENDIX A. Tables of Experimental Data

Al. Description of Stone Treatments

A2 . Description of Paints

A3 . Water Absorption of Treated Stone

A4 . Water Vapor Transmission (WVT)

A5. Resistance to Sodium Sulfate

A6. Compressive Strengths of Treated and Untreated Stones

A7 . Depth of Penetration of Treatments in Sandstone Specimens,

Laboratory Testing

A8 . Depth of Penetration of Treatments Applied in Field

A9 . Results of Accelerated Weathering Test

AlO. Results of Adhesion Testing of Paints

All. Results of Water Vapor Condensation Testing of Painted

and Treated Stone

Al
Table Al. Description of Stone Treatments

Treatment Designation Generic Type Comments

A Acrylic prepolymer, dissolved

in solvent

SI Silane ethyl silicate^, with

hardener

S2 Silane^ ethyl silicate^, with

hardener and water

repellent.

S3 Silane^ ethyl silicate^, with

water repellent

S4 Silane^ ethyl silicate^,

with hardener

^Reacts with water, in the presence of a catalyst, to form

hydrated silica.

^Treatments S2, S3, and S4 were obtained from the same supplier.

A2
Table A2 . Description of Paints

Paint Designation^ Generic Type Comments

Acrylic based Applied by supplier,

coverage not known.

SI Latex Two coats

recommended

.

Coverage, 200-275

ft^/gal., first

coat and 150-200

ft^/gal. second

coat.

S2, S3, and S4^ Latex Two coats

recommended

.

Solid content is

45%. Coverage, 125-

150 ft^/gal., first

coat and 150-175

ft^/gal. second

coat.

^Paints were obtained from suppliers of stone treatments and are

identified by the same designation code as the treatments with

which they are used.

^Stone treatments S2, S3, and S4 were obtained from the same

supplier. The same paint was applied over each of these three

silanes.

A3
Table A3 . Water Absorption of Treated Stone

Ratio of Water Absorption of Treated to

Untreated Stone^

Treatment

Desianation^ Sandstone, Limestone

Dercent oercent

A 53 11.9

SI 4.3 4.1

S2 5.3 3.4

S3 5.3 18.4

S4 8.4 10.6

^Measured using ASTM C 97 (7)

^Treatments were applied by their respective suppliers.

A4
Table A4. Water Vapor Transmission (WVT).

Treatment Ratio of WVT of Treated eind/or Painted Stone to WVT of Untreated and Unpainted Stone

Designation^ Treated Stone Treated Stone with Paint Untreated Stone with Paint

Sandstone Limestone Sandstone Limestone Sandstone^

A 1.01 0.26 N.T.^ 0.26 N.T.

(0.14)*^ (0.07) (0.04)

SI 1.07^* 0.39 1.07 0.34 N.T. (0.04) (0.01) (0.05) (0.07)

S2 1.03 0.68 0.63 0.35 0.95®

(0.01) (0.01) (0.20) (0.01) (0.07)

S3 1.0 0.73 0.40 0.31 0.95e

(0.01) (0.01) (0.14) (0.07) (0.07)

S4 0.73 0.57 0.48 0.34 0.95e

(0.01) (0.01) (0.13) (0.07) (0.07)

^Specimens prepared by treatment supplier. except where noted otherwise.

^.T. denotes not tested because specimen or material not available.

^Values in parenthesis are standard deviations for triplicate specimens.

^Specimens prepared by NBS by applying treatment and paint with brush.

O Coverage approximately 200 ft /gal.

®Same paint used with treatments S2, S3, and S4.

A5
Table A5. Resistance to Sodium Sulfate^

Treatment Number of Cvcles to Failure^^

Designation^

A

Sandstone

8

Limestone

7

SI 9 6

S2 11 8

S3 13 10

S4 13 10

Untreated 7 4

^Treatments applied to stone specimens by respective suppliers.

^Data obtained by using ASTM Designation C 88 (9)

•^Results are average of two specimens.

A6
Table A6. Compressive Strengths of Treated and Untreated Stones

Material Compressive Strength^ Designation Sandstone Limestone

c.v.b.

%

psi MPa C.V.^

%

psi MPa

A 5720 39.4 5.1 5737® 39.6

SI 4400^

5660^

8050®

30.3

39.0

55.5 10.1

5640® 38.9

S2 5150 35.2 8.0 5875 40.5 8.2

S3 6700 46.2 1.4 6320 43.6 1.3

S4 5540 38.2 0.5 6580 45.4 3.3

untreated 5790 39.8 10.7 5170 35.6 3.3

^If not specified, triplicate specimens (2 in (51 mm) ) prepared

by supplier of treatments were tested according to ASTM Designation

C 170 (10)

.

^Coefficient of variation, in percent, designated by c.v.

obtained by dividing the standard deviation for a set of data by

the average of the set.

"^Single specimen provided by treatment supplier.

•^Triplicate specimens prepared by NBS using a paint brush.

Treatment applied until surface was saturated.

^Triplicate specimens prepared by NBS by immersing specimens in

treatment.

A7
Table A7 . Depth of Penetration of Treatments in Sandstone

Specimens^, Laboratory Testing

Treatment Designation Depth of Penetration^ Method of

inch mm Application

A 1 25 pressure

injection

SI 0.3 8 brush

S2 0.8 20 dipping

S3 0.8 20 dipping

S4 0.8 20 dipping

^Specimens were 2

suppliers.

in (51 mm) cubes. Treatments were applied by

^Estimated error in measurement is 0.13 in (3.3 mm) .

A8
Table A8 . Depth of Penetration of Treatments Applied in Field

Treatment

Designation Sandstone Limestone

inch mm inch mm

Method of

Application

<1 week after application^

3.5 89 2.9 74 pressure injection.

(0.20)^ (5.1) (0.13) (3.3) by supplier

32 days after apploication

4.4 112 3.3 84

(0.3) (7.6) (0.04) (0.1)

<1 week after application

0.65 17 0.60 15 two coat application

(0.03) (0.76) (0.03) (0.76) brush, performed

by NBS

32 davs after application

1.0 25 0.62 16

(0.09) (2.3) (0.09) (2.3)

<1 week after application

1.5 38 1.3 33 sprayed, by

(0.08) (2.0) (0.07) (1.8) supplier

32 davs after application

2.2 56 1.4 36

(0.2) (5.0) (0.05) (1.3)

^Values in parenthesis are standard deviations of a set of

triplicate measurements.

^Within one week after application.

A9
Table A9 . Results of Accelerated Weathering Test^

Treatment

Designation^ Condition after 1660 Cycles

A Sandstone: No cracking,

surfaces.

brown stains on

Limestone: No cracking,

appearance.

no change in

SI Sandstone: No cracking,

surfaces.

brown stains on

Limestone: No cracking,

appearance.

no change in

S2, S3, & S4 Sandstone: No cracking,

surfaces

.

brown stains on

Limestone: No cracking,

appearance.

no change in

untreated stone Sandstone: No cracking,

surfaces.

brown stains on

Limestone: No cracking,

appearance.

no change in

^Duplicate specimens tested using apparatus described in Section

6.6. No painted specimens were tested.

^Treated stone prepared by supplier of treatment.

AlO
Table AlO. Results of Adhesion Testing of Paints^

Treatment and/or Paint Desianation

Test Specimen A SI S2 S3 S4

Sandstone painted, untreated

PS I N.A.^ 288 619 619^ 619^

MPa 2 .

0

4.3 4.3 4.3

C.V.^ 4.5 16 16 16

Failure pe S® S S

Sandstone painted. treated

PS I 482 227 604 567 619

MPa 3 .

3

1.5 4.2 3.9 4.3

C.V. 40 37 6.3 4.4 3.9

Failure P P S S S

Limestone painted. untreated

PS I N.A. 307 526 526^ 526

MPa 2.1 3.6 3.6 3.6

C.V. 16 0.8 0.8 0.8

Failure P S S S

Limestone painted. treated

PS I 475 228 507 528 537

MPa 3.3 1.5 3.5 3.6 3.7

C.V. 47 25 2.6 4.5 6.9

Failure P P S S S

^Tested according to ASTM Designation D 4541.

^Coefficient of variation in percent. Triplicate specimens.

^Painted specimen or paint not submitted by supplier.

‘^Same paint as with treatment S2.

®P indicates failure in paint film, S indicates failure in stone.

All
Table All. Results of Water Vapor Condensation Testing of

Painted and Treated Stone^

Paint-Treatment

Designation Condition of Paint after 40 Davs of Testing

No blistering of paint on either treated or

untreated sandstone and limestone test

panels. Brown stains on top (unexposed)

surface of sandstone test panels.

Sl*^ No blistering of paint on either treated or

untreated sandstone or limestone test panels.

Brown stains on top (unexposed) surface of

sandstone test panels. Paint had softened and

was easily removed with a spatula.

S2 , S3, & S4*^ Same paint for S2

,

S3 and S4. No blistering

of paint on any test panel. Brown stains on

top surface of sandstone test panels. No

visually observable deterioration of paint.

^Tested using apparatus and procedures described in ASTM

Designation D 2247.

^Test stone panels prepared by supplier of paint-treatment

system. Tested in triplicate.

•^Test stone panels prepared by NBS. Tested in triplicate.

Paint coverage was approximately 200 ft^/gal.

^Test stone panels prepared by NBS. Tested in duplicate.

Paint coverage was approximately 150 ft^/gal.

A12
NBS-114A (REV- 2-BC) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No, 3. Publication Date

SHEET (See instructions) NBSIR 87-3542 October 1987

4. TITLE AND SUBTITLE

Preliminary Performance Criteria for Stone Treatments for the United State Capitol

5. AUTHOR(S)

James R. Clifton

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE 8, Type of Report & Period Covered

GAITHERSBURG, MD 20899

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Bureau of Standards

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most si gnificant information. If document includes a significant

bibliography or literature survey, mention It here)

The West Central Front of the United States Capitol is being restored, including

cleaning and repainting the sandstone, and replacing badly deteriorated sandstone

with Indiana limestone. Application of stone treatments was proposed as a way of

extending the lives of the sandstone and paint. However, without adequate

selection criteria there was no certainty of effective performance by stone

treatments. The purpose of this study was to develop performance criteria to

assist in the selection of stone treatments.

Based on an analysis of expected deterioration processes, it is concluded that

deterioration of the sandstone was most likely associated wi th water penentration

into the exposed outer surface. Therefore, if a treatment is to be used, it

should protect the outer surface of the sandstone from rain penetration. In

addition, the treatment should penetrate and consolidate any deteriorated stone.

Also, treatment should not cause premature failure of the paint. Based on these

requirements, four preliminary performance criteria were developed, but have not

been verified by long-term studies. Of five stone treatments evaluated, one met

the four criteria. It is recommended that treatment be used on areas of deteriorated

sandstone needing consolidation and on stone in areas subjected to the most

severe weathering locations.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

consolidation, limestone, paint, performance criteria, restoration,

sandstone. United States Capitol, weathering

13. AVAILABILITY

Xy

I

Unlimited

I I For Official Distribution. Do Not Release to NTIS

14. NO. OF

PRINTED PAGES

42

I I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $11.95

USCOMM-DC 6043-P80
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