Attachment_9,_Shaw_Memorial_Report_Final_red.pdf

August 2013

BUILDING CONSERVATION ASSOCIATES INC

Shaw Memorial Boston, Massachusetts

Existing Conditions and Treatment Recommendations

August 2013

Shaw Memorial Boston, Massachusetts

Existing Conditions and Treatment

Recommendations

Prepared For Friends of the Public Garden

69 Beacon Street Boston, MA 02108

Prepared By

Building Conservation Associates, Inc.

10 Langley Road Suite 202

Newton Centre, Massachusetts 02459

BCA Team Lisa Harrington Andrea Gilmore

Shaw Memorial Page 1 Existing Conditions and Recommendations

BUILDING CONSERVATION ASSOCIATES INC August 2013

Shaw Memorial 24 Beacon Street Boston, Massachusetts

Existing Conditions and Treatment Recommendations

INTRODUCTION

On Thursday, August 1, 2013, Building Conservation Associates, Inc. (BCA) surveyed the exterior conditions of the Shaw Memorial in Boston, Massachusetts. The goal of the inspection was to assess the recent repairs to the Memorial and to comment on its structural condition.

The conditions of the Memorial’s masonry were documented with digital photographs that are included in this report.

This report summarizes the findings of BCA’s survey and provides a general list of recommendations for treatment of the Memorial’s historic masonry elements based on those findings.

Building History and Description

The Shaw Memorial was built in 1897 to commemorate Robert Gould Shaw and the Massachusetts 54th Regiment. The Memorial is a granite and marble structure designed by the architectural firm McKim, Mead and White. At the center of its north face (Beacon Street) is Augustus Saint-Gaudens’ bronze relief sculpture that depicts the 54th Regiment marching down Beacon Street during the Civil War. In front of the sculpture is a brick terrace that surrounds two elm trees. The elm trees, reputed to have been planted by John Hancock, pre-date the Memorial and were incorporated into its original design.

The base of the Memorial is constructed of Milford granite, and the steps that flank the Memorial are also granite. The fountain and the benches on the south (Common) side of the Memorial are granite as well. Above the terrace, the railings and stonework that surrounds the bronze sculpture is marble. The benches on the terrace are marble and the terrace paving is brick. (Figures 1 – 4)

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BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 1 – Shaw Memorial at Beacon Street. Note St. Gaudens’ sculpture and flanking elm trees. On a rainy day, the Memorial marble is quite pink.

Figure 2 – Shaw Memorial drawings from A Monograph of the Works of McKim, Mead and White, Da Capo Press, New York, 1985.

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BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 3 – Southeast corner of Shaw Memorial showing weathered marble rail, polished marble benches and modern brick terrace paving.

Figure 4 - South wall of Shaw Memorial showing Milford granite base and marble rail.

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Figure 5 - Heavy bioligical growth due to proximity and shade of large nearby trees.

Restoration History

BCA completed drawings and specifications for masonry repairs to the Memorial for Ann Beha Architects in April of 2005. Work was done on the Memorial in 2009 (Joseph Gnazzo Company, Inc.) and in 2012-13 (Cenaxo, LLC). It is not known whether BCA’s drawings and specifications were used for this work and BCA was not involved in monitoring either the 2009 or 2013 work. The proposals for the scopes of work undertaken in 2009 and 2013 are appended to this report.

EXISTING CONDITIONS

Stone

The granite components of the Memorial are in very good condition. Milford granite is a high quality granite that was widely used in Boston at the turn of the century. McKim Mead and White used it for the Boston Public Library.

The marble is also in good condition, though its surface is abraded and sugared in some areas.

This rough surface has fostered the biological growth that darkens its light pink color. The surface damage to the marble has likely been caused, in part, by repeated and aggressive cleaning. Acid cleaners should not be used on marble.

Soiling

The primary soiling on the Shaw Memorial is biological growth, largely due to the proximity of the trees on the sidewalk between the Memorial and Beacon Street. There is also a limited amount of atmospheric, or general soiling due to the Memorial’s urban setting (Figure 5).

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Figure 6 - Rose colored repointing mortar that is discolored and has cracked away from the stone.

Pointing

The pointing on the Memorial is in fair to poor condition. Recent repair projects have had limited scopes of work that have utilized a variety of sealants and mortars, have been executed with varying levels of quality, and have failed to address the problem of water entering the Memorial comprehensively.

Mortar

The most recent repair campaign (2013) included repointing with a mortar that is much too hard for the marble and granite. This mortar exhibits a variety of types of failure. In many locations, the mortar has cracked, shrunk, or is missing altogether. In some areas, there is already moss growing in open joints. Its rose color has also turned pink or white in many locations, indicating that it was likely installed during improper weather conditions. Mortar that is installed when it is too hot or too cold does not cure properly. Based on the date of their 2012 proposal, the Cenaxo work may have either been done in the late fall or early spring when the temperatures were too cold.

In addition to the inappropriate hardness of the 2013 repointing mortar, the color does not resemble the original mortar (Figures 6,7)). This mortar is rose colored, where as the original mortar was more buff colored. (Analysis of a sample of the original mortar is included at the end of this report).

The condition of the mortar joints is allowing water to penetrate into the Memorial. During removal of mortar samples for analysis, BCA discovered the bedding mortars are completely saturated. This indicates on going water infiltration and widespread failure of the current repointing mortars. Staining patterns after a rainstorm reveal the many locations that water is entering the Memorial through deteriorated mortar joints. (Figure 8).

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Figure 7 – Original bedding and pointing mortar exposed behind later pointing mortar.

Figure 8 - Note staining of the stone after a rainstorm showing how the water is entering and running down the Memorial.

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BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 9 - Rose-colored sealant in wide joint, southwest corner of railing. Sealant joint has already failed.

Sealant

A rose colored sealant has been used to fill the wide joints in the Memorial railing and at the projecting stone in front of the sculpture. Sealant is the correct choice for the pointing of these joints because they are so wide and continue to move. The color of the sealant, however, should match the marble. A matching color would make the joints much less conspicuous and would more nearly replicate the original mortar joints. (Figure 9)

The sealant around the bronze sculpture is the correct color and blends well. In some locations it is not well adhered. (Figure 10) It should be carefully monitored and replaced as necessary.

Since it adjoins the St. Gaudens’ sculpture, removal of the existing sealant should be done with the supervision of a conservator.

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BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 10 – Failure of sealant around the bronze sculpture at the junction of a mortar joint.

Mortar joint is open.

Figure 11 – Displaced stone at the east side of the Memorial.

Structural Issues

The most significant stone movement occurs on both of the side stair walls, including the walls and railings above (Figure 11-13). This movement appears to have been caused by water entering the stone from the brick terrace. Over time, in conjunction with freeze/thaw cycling, Shaw Memorial Page 9

BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 12 – Displaced stone at the west side of the Memorial.

Figure 13 – Detail of displaced stone at the west side of the Memorial.

this condition has caused the mortar joints to become wider and the stone to move. It is a classic terrace condition, aggravated by the permeability of the brick paving and the presence of the two large trees in the terrace. In its current condition, the joints at the base of the balustrade have failed and water is actively entering the stone wall. With each winter that this condition exists, the stone will continue to move.

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BUILDING CONSERVATION ASSOCIATES INC August 2013

Figure 14 – Stainless steel pin at horizontal joint of on the upper stones.

The main body of the Memorial exhibits little stone displacement. There are a few stones at the corners of the foundation that have moved slightly, and this appears to be from the same water problem as at the side rails.

As part of this inspection, BCA was able to view the top of the Memorial with the aid of an extension ladder. There are stainless steel clamps that tie the capstones together. The existing clamps replaced earlier clamps that have been removed and their locations filled with mortar.

(When the existing clamps were installed, the capstones may have been removed and reset.

There is a flashing under these stones and their bedding mortar is different from the bedding mortar found elsewhere in the Memorial, all of which suggest that they have been re-set.) The clamps undoubtedly explain why there has been little stone displacement in this part of the Memorial.

The horizontal joints between the capstones have been filled with a black sealant that is showing signs of failure (Figure 14). Staining on the Memorial after rainstorms indicates that water is entering the stone through these joints. The joints should be repaired with sealant and lead-T’s.

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BUILDING CONSERVATION ASSOCIATES INC August 2013

SUMMARY OF FINDINGS/TREATMENT RECOMMENDATIONS

The existing conditions of the Shaw Memorial reveal the inherent difficulties of maintaining a historic structure without comprehensive repair. If the Memorial was to be repaired as comprehensively as possible, it would involve extensive stone disassembly and rebuilding and possibly the removal and reinstallation of the bronze sculpture. The existing condition of the Memorial does not merit this level of repair and as long as the elm trees are part of the Memorial, significant rebuilding of the masonry is not recommended. The elm trees might be damaged by the masonry work and their continued presence will cause movement in the Memorial’s masonry. When the trees are removed will be the logical time to consider this level of repair.

In the meantime, it is very important to comprehensively repoint the Memorial to prevent water from entering the stone at its current rate. The on-going water penetration is causing additional movement of the stone, accelerating the deterioration of the stone, and generating the disfiguring biological growth. Although work has been done on the Memorial recently, the best course of action will be to start anew so that all of the joints are cleared and pointed with the same mortar and sealant. Installation of lead T’s at the horizontal joints of the capstones will also significantly reduce the water entering the Memorial.

The items of work should be as follows:

• Clean masonry 100% to remove general soiling and biological growth.

• Properly prepare and rake back 100% of joints (both mortar and sealant joints).

• Install new sealant (colored to match original mortar) in all joints in the north and south side walls, rear (east) wall, railings and benches.

• Install mortar to match original mortar in all remaining joints.

• Install lead “T” joint covers on horizontal marble joints in the capstone above the bronze sculpture.

The work should be done with a full set of drawings and specifications and with project monitoring by an architectural conservator.

10 Langley Road

Suite 202 Newton Centre, MA

02459 T 617.916.5661

Laboratory Report: Mortar Analysis

Date: August 9, 2013

Commissioned By: Friends of the Public Garden

Building/Project: Shaw Memorial Building Address: 24 Beacon Street, Boston, MA

Construction Date: 1897

No. of Samples: 1

Samples Removed by: BCA, Inc.

Analysis Performed by: L. Harrington

Analysis Checked by: L. Harrington

MORTAR ANALYSIS

The objective of this mortar analysis is to characterize the original mortar used to point the masonry at the Shaw Memorial, in Boston, Massachusetts. The information obtained from analysis will be used to assist in formulating an appropriate mortar mix for masonry restoration.

This mortar analysis has been prepared for the Friends of the Public Garden.

METHODOLOGY

Samples

One representative mortar sample (SM-1) was removed from the west elevation on the pilaster to the north of the bronze plaque. This example of original mortar was found behind two repointing campaigns, one the most recent, a very hard reddish-pink mortar, and a similarly colored reddish-pink mortar behind that. This original mortar sample is fairly soft, and can be broken by hand. The intact mortar sample exhibits a light gray color, very similar in color to the limestone on the Memorial.

Laboratory Analysis

In the laboratory at BCA, the sample of mortar from Shaw Memorial was analyzed according to procedures developed by the National Park Service. Visual characterization was performed to assess the overall appearance of the mortar. The sample was examined under a Nikon SMZ-U stereo-binocular microscope with fiber optic light source and a magnification up to 100X.

Observations were recorded and the mortar was matched to Munsell® Standard Soil colors.

The mortar was analyzed via wet chemical technique to separate the samples into their three

BUILDING CONSERVATION ASSOCIATES INC Page 2 constituent fractions (acid soluble component, fines and sand) by acid digestion and gravimetric analysis. Acid digestions methods do not generally give reliable results when:

- significant quantities of Portland cement are present in the mortar

- portions of the sands contain calcareous aggregate

- the mortar being analyzed is in a deteriorated state

- natural cement is present

- hydraulic lime is present

Given the limitations that exist within the wet chemical technique, it is usually the case that the greatest value of this analysis is to isolate the sand portion of the mortar sample for viewing this component separately from the binder. Separated sands can then be matched to commercially available sands for replacement mortar mixes.

Further information such as the aggregate to binder ratio, and the identification of specific crystalline materials present within the aggregate and binder can be determined by other analytical techniques such as petrographic analysis and x-ray diffraction. In conjunction with the standard wet chemical technique, these tests can provide a more comprehensive understanding of the composition of the mortar. For matching the original aggregate, wet chemical analysis is considered to be the most appropriate, initial analytical procedure.

Wet Chemical Analysis Method

The sample was ground in a mortar with a pestle and soaked in a 3 Molar solution of hydrochloric acid. The acid dissolves the lime and cement in the mortar, enabling the sands and fines to be separated. As the mortar dissolves, the sand is repeatedly washed with distilled water and filtered to separate the fines from the sand. The sample effervesced heavily in the acid, as is typical of lime-containing mortars.

After separation, the aggregate (course sand) and the fines (pigments and clayey silt) were dried.

Once dried, the aggregate and fines were weighed and their percentage contributions to the mix were calculated. These calculations do not identify the exact proportions of the original mortar, but do give an approximation of its proportions. These proportions are used to determine a suitable modern repointing mix that is compatible with the original mortar and the masonry material being repointed. The proportions of the analyzed mortar are recorded on the attached data sheets.

The sand portions of the sample were sieved through a standard sieve set that determines the size and distribution of the aggregate. Replicating the size, distribution, and color of the sand is crucial to recreating a mortar that matches the appearance of the original. Samples of the sands, with their particle size and distribution, are included with this report for matching.

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The fines were collected and used to help determine whether pigments will be required to replicate the original mortar. Any pigments or silt in the original mortar are present as a portion of the fines. Samples of the fines are included with this report for color matching.

SUMMARY OF FINDINGS

The original pointing mortar at Shaw Memorial is a fairly soft mortar that is light gray in color.

The sand grains of sample SM-1are primarily rounded to angular in shape and consist primarily of translucent quartz particles. There is a small amount of white quartz particles, and a very small amount of black, green, gray, yellow, and red particles.. The large quantity of the translucent quartz grains give the overall color of the sands a somewhat light color value. The sands are primarily fine in size, and, when sieved through a screen, the distribution produced is weighted towards the finer (#50 and #100) screen sizes.

The fines comprise approximately 12% of the mortar mix and are light warm gray in color (Munsell® Standard Soil color 10Y 7/2-8/2). This is a fairly large percentage of fines, which largely contributes to the overall light gray color of the mortar.

TREATMENT RECOMMENDATIONS

Lime, sands or other foreign matter can wash out of a mortar over time and alter the original ratio of components. This erosion can cause the proportions of cement, lime and sand obtained by wet chemical analysis to become skewed in old mortars. The mortar recommended for repointing the masonry at Shaw Memorial is a Portland Cement-lime-sand based mortar mixed at a ratio of 1:2:7 (cement:lime:sand) by volume. This mortar is not an exact replication of the original mortar mix, but is a standard mortar mix that can be readily replicated by a mason and will be compatible with the existing masonry and the climate in which the joints will have to perform. A 1:2:7 ratio is a Type N mortar by property (specifically compressive strength). This mix is recommended because a Type N mortar, as defined by ASTM C270-06, is commonly used for exterior above-grade masonry elevations. This proportion has been chosen to approximate the plastic and conductive properties of the original mortar, while providing a durable material for pointing the masonry joints.

To replicate the visual qualities of the original mortar, the sand used for repointing mortar should match that of the original mortar in color and particle size. The color of the sands is critical to recreating the overall appearance of the cured mortar. The sand should comply with ASTM C-144 and should be approved before the mortar mixes are prepared. The Schofield Sand Company in Bound Brook, New Jersey (tel: 732.356.0858) sells a good selection of bagged sand and will provide samples upon request.

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Although the sand color generally gives the overall color of a mortar, pigments can be used to adjust the color. Any additional pigments required should be based upon the color of the fines samples. If the addition of pigments is deemed necessary to match the original mortar then these tinting pigments should meet the standards of ASTM C979. "Pigments which are not described by C979 are permitted if demonstrated by their history of performance under equivalent conditions and mortar formulation to be non-detrimental to the mortar"1. The pigments selected for this mortar should be stable, non-fading and alkali resistant (lime-proof) pigments as needed, not to exceed 10% by weight of the total binder weight, except for carbon black which is limited to 2% by weight of the total binder weight, to match the original mortar color. and should not exceed 10% of the weight of the Portland cement used in the mix. The cement used should be Type I Portland cement, conforming to ASTM C-150. The lime should be Type S lime, conforming to ASTM C-207.

Prior to the general repointing, samples of the repointing mix should be prepared and approved.

Several samples may have to be mixed to achieve the correct mortar color. The matching should be performed on cured samples of the mix that have been washed and thoroughly dried.

Samples of the approved repointing mortar should be installed in the wall to establish the correct joint profile. The approved pointing sample should remain in place for the duration of the project and serve as the standard for acceptable work.

1 ASTMC1713-10 Standard Specification for Mortars for the Repair of Historic Masonry, 2010, Conshohocken: ASTM International, 2.

Building Conservation Associates, Inc.

LABORATORY REPORT: MORTAR CHARACTERIZATION

SAMPLE NUMBER:

Date: 8.7.13

Site: Shaw Memorial

Construction Date: 1897

Location: 34 Beacon Street, Boston, MA

Analysis Commissioned By: Friends of the Public Garden

Samples Removed By: LH

Laboratory Procedure: NPS

Analysis Performed By: LH

Elevation: West Elevation

Sample Location/Mortar Type: Pilaster to the north of the bronze plaque

ANALYSIS

OBSERVATIONS

Mortar Color: 7.5 YR 8/1

Hardness: Moderately soft

Condition of Mortar: Partially deteriorated

Surface Characteristics: Weathered

Mortar Texture: Smooth

Fines Color: 10 YR 7/2-8/2

Aggregate Characteristics: Primarily translucent rounded and angular quartzite. Small amount of white quartzite. Very small amount of black, green, yellow, gray and red particles. Particle size is relatively uniform and small in size.

DATA

Weight (in grams):

Original Sample: 19.30

Aggregate: 7.78

Acid Soluble Material: 9.29

Fines: 2.32

Weight (percentage of whole):

Aggregate: 40%

Acid Soluble Material: 48%

Fines: 12%

Recipe Obtained by Analysis (lime:sand): 1:1

Aggregate Characterization:

Sieve Screen # Mesh Size Weight (g) % Retained

16 1.18 mm 0 0%

30 600 micron .18 2%

50 300 micron 2.71 35%

100 150 micron 4.06 52%

PAN Fines .83 11%

RECOMMENDED REPAIR MIX (cement:lime:sand): 1:2:7