Analyze Historic Brick Report Section.pdf

Selfridge ANGB Conceptual Report

Analyze Historic Brick

Final Submittal - Revised March 11, 2009

Prepared By:

25200 Telegraph Rd., Ste. 200

Southfield, MI 48033 P: 248-936-8000; F: 248-936-8111

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TABLE OF CONTENTS

1.0 INTRODUCTION

2.0 EXECUTIVE SUMMARY

3.0 BUILDING CONDITIONS AND RECOMMENDATIONS

3.1 Existing Conditions

3.2 Recommendations

4.0 GENERAL CONSIDERATIONS FOR MASONRY RESTORATION

4.1 General Comments

4.2 Project Conditions

4.3 Repointing Masonry

4.4 Cleaning Existing Masonry

4.5 Potential Cleaning Problems

4.6 Final Cleaning

4.7 Water Repellents and Antigraffiti Coatings

4.8 Environmental Considerations

4.9 Referenced Standards

4.10 References

5.0 SAMPLE REPAIR SPECIFICATIONS

5.1 Part 1 – General

5.2 Part 2 - Products

5.3 Part 3 - Execution

6.0 SME REPORT

7.0 APPENDIXES

7.1 Building Photos

HANGERS 5 & 6 PHOTOS

BUILDING 50 PHOTOS

BUILDING 118 PHOTOS

BUILDING 126 PHOTOS

BUILDING 127 PHOTOS

BUILDING 128 PHOTOS

BUILDING 130 PHOTOS

BUILDING 140 PHOTOS

BUILDING 160 PHOTOS

BUILDING 162 PHOTOS

BUILDING 305 PHOTOS

BUILDING 340 PHOTOS

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7.2 Building Plans

HANGARS 5 & 6

BUILDING 50

BUILDING 118

BUILDING 126

BUILDING 127

BUILDING 128

BUILDING 130

BUILDING 140

BUILDING 160

BUILDING 162

BUILDING 305

BUILDING 340

7.3 Building Drawings

HANGARS 5 & 6 DRAWINGS

BUILDING 50 DRAWINGS

BUILDING 118 DRAWINGS

BUILDING 126 DRAWINGS

BUILDING 127 DRAWINGS

BUILDING 128 DRAWINGS

BUILDING 130 DRAWINGS

BUILDING 140 DRAWINGS

BUILDING 160 DRAWINGS

BUILDING 162 DRAWINGS

BUILDING 305 DRAWINGS

BUILDING 340 DRAWINGS

7.6 Standard Repair Details

7.7 Example Construction Documents

7.7.1 Example Bid Form

7.7.2 Example Drawings

7.8 Brick Industry Association Technical Notes

7.9 Brick Maintenance Unit Costs

8.0 DESIGN SCHEDULE

9.0 MEETING MINUTES

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1.0 INTRODUCTION

This report is to summarize the evaluation of the existing historic brick problems on several historic buildings at the Selfridge Air National Guard base. The work scope includes testing of existing brick on deteriorating buildings and the testing of some mortar samples. Buildings have been repaired over time, and in many cases, patched brick does not match that of the original buildings. In some cases existing brick is spalling causing potential moisture intrusion problems.

Giffels/IBI Group was retained by Selfridge ANG to help develop standards for future repairs where masonry is being renovated. The report was to include findings and recommendations to protect and\ or repair existing historical brick. The report will provide a base standard for the protection and repair of deteriorated historic structures and to provide a standard approach, details and quad specifications to utilize for future site building exterior wall renovation projects.

To adequately analyze the existing brick condition, Giffels/IBI Group subcontracted the services of a testing agency, Soils and Materials Engineers, Inc. of Plymouth, Michigan.

Although a total of 13 buildings were included in the scope of this report, brick samples and brick testing were performed on 10 of the existing Selfridge site buildings:

o Hangers 5 & 6 o Building 50 – Not analyzed o Building 118 o Building 126 o Building 127 o Building 128 o Building 130 – Not analyzed o Building 140 o Building 160 o Building 162 o Building 305 o Building 340 – Not analyzed

These buildings were all originally constructed around the 1920’s and early 1930’s. Some of the main referenced standards utilized in this report include:

o Selfridge Vision 2010 Design Standards o ASTM C 216 o ASTM C 67 o AIA Masterspec and AIA Masterspec Supplementary Evaluations o Brick Industry Association Technical Notes p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 4

Additional minor references are included in Section 4.10 of this Report.

Per search of the Selfridge drawing archives for each of the buildings, the following was discovered with regard to the history of building repairs. The list below is a representative list of repairs made over time, but it is not considered to be an exhaustive list since it was limited to only those projects discovered in the drawing files.

Hangers 5 & 6 o 1965 General Renovations o 1985 Roof Replacements and Repairs and Brick on Block Infills North & South o 1996 Catwalk and Ladders Addition

Building 50 o 1960 Roof Replacement - Slate o 1973 Roof Maintenance Repairs o 1977 New Fire Escape Addition o 1986 Roof Maintenance Repairs o 1994 Interior Renovations o 1997 Mechanical Upgrades

Building 118 o 1951 Gutters and Roof Repair o 1965 Mechanical Upgrades and Fire Sprinklers Addition o 1976 Roof Repairs o 1977 Energy Conservation Upgrades o 1992 Roof and Eave Repairs o 1998 Roof Repairs

Building 126 o 1970 General Building and Roof Repairs o 1982 Roof Repairs o 1993 Interior Demolitions and Renovations

Building 127 o 1958 Building Rehabilitation o 1961 Utility Upgrades o 1962 Interior Renovations o 1965 Air Conditioning System Addition o 2000 New Standing Seam Roofing and Gutters o 2001 Major Interior and Exterior Building Renovations and Upgrades

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Building 128 o 1972 Building Alterations and Doors Replacement o 1982 Roof Repairs o 1985 New Windows and Building Siding o 1986 Vehicle Wash Renovation o 1988 Building Interior Renovation o 1991 Interior Painting

Building 130 o 1942 Building Alterations o 1956 Building Addition and Cooling Tower Addition o 1959 Interior Renovations o 1962 Air Conditioning Upgrades o 1976 Lighting Repairs o 1991 New Building Addition o 1998 Roof Repairs

Building 140 o 1952 New Fire Escape o 1962 Interior and Exterior Repairs o 1965 Interior and Exterior Repairs o 1985 Roof and Scupper Repairs

Building 160 o 1954 New Building Addition o 1957 Interior and Exterior Renovations o 1958 New Fire Sprinklers Addition o 1961 New Building Entrance o 1984 New Boiler and Interior Renovations o 1986 Roof Repairs

Building 162 o 1938 New 2 Bay Addition o 1951 Interior Renovations and Underground Utilities o 1962 Interior Renovations

Building 305 o 1994 Repair Windows

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Building 340 o 1964 Repair Storm o 1974 Door and Wall Replacements and Repair o 1976 Building Renovations o 1982 Building Renovations o 1992 Utilities Upgrade

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2.0 EXECUTIVE SUMMARY

The existing brick on historic buildings at the Selfridge site vary in their need for repair. A more organized and technically sound approach is needed for future renovations of these masonry structures and to ensure the longevity of these buildings.

The project entails the review and inspection of 13 sample historic buildings on the Selfridge campus for the purposes of historic renovation and repair. The report provides an analysis on a range of years in which the brick structures were constructed at the Base. The Statement of Work is as defined in the Selfridge Project VGLZ 072048, SOW, Historic Building Brick Analysis, dated August 15, 2007.

The buildings were originally constructed in the 1920’s and early 1930’s, and have been repaired periodically over the years and are currently experiencing additional deterioration and obsolescence. Major problems include brick and masonry deterioration and moisture penetration and migration. Construction practices and brick construction techniques, in the 1920s and 1930s were not as advanced as they are today. In many cases, mismatched brick was used to patch and repair problems areas. Since contemporary brick and mortar is generally harder than that utilized in the early part of the 20th century, past repairs have compounded the masonry wall problems.

The SME Report on the brick and mortar samples indicate a softer, more absorptive, type brick than is generally used today. The mortar sample also indicates a low cement, highly porous, mix than is typically used today.

The scope of work will include a building by building general inspection and analysis for the purposes of creating generic type repair details and masonry restoration specifications to use as a guide for future renovation and construction projects. Potential sources of water intrusion include roofing and flashing conditions, rusted steel lintels, lack of vapor barriers, improper patching\ repairs, including non-matching brick and mortar, deteriorated sealant joints, mortar joints in need of tuckpointing, improper wall construction and lack of wall weeps.

A proper method of repairing these structures includes up front testing for both brick and mortar, technically sound and specific construction document drawings and specifications for repair\ replacement, and good construction follow up to assure that construction repairs meet the intent of the contract documents. In this way, we can assure the continued life of these historic structures for many years to come. The report includes general considerations, sample repair specifications, standard repair details, example construction documents and brick industry tech notes. Use of the recommendations included in this report are provided to form the foundation of quality future renovation.

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3.0 BUILDING CONDITIONS AND RECOMMENDATIONS

3.1 Existing Conditions

The existing brick system and disposition of existing masonry conditions and related contributing components are summarized as follows:

Hanger 5 and 6

Some recent renovations on the north and south elevations of the building has resulted in good brickwork and mortar joints for the majority of the building faces. However, in original building brickwork there exist the following problem areas:

o In good shape at newer north and south infills, but with some deteriorated and failing brick mortar joints o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Parapets, gutters and roof flashings experiencing obsolescence o Deteriorating sealant at materials abutting masonry (doors, windows, etc.)

o Generally in good shape, but with some deteriorated and failing brick mortar joints o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Gutters and roof flashings experiencing obsolescence o Deteriorated and failing brick mortar joints o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 9 o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Building was recently renovated but has existing spalling and cracked brick in some locations o Lack of flashing and weeps at lintels and interruptions in masonry

Building 128 o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 10 o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry

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Building 340 o Generally in good shape, but with some deteriorated and failing brick mortar joints o Existing spalling and cracked brick in some locations o Rusting door and window lintels o Lack of flashing and weeps at lintels and interruptions in masonry

O Deteriorating sealant at materials abutting masonry (doors, windows, etc.)

3.2 Recommendations

Generic repair recommendations for the existing brick system are summarized as follows:

Hanger 5 and 6 o Tuck point existing deteriorated and failing mortar joints o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets, gutters and roof flashings that are part of the exterior wall construction o Clean and seal exterior brick facades o Provide new sealant at all materials abutting masonry (doors, windows, etc.)

o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required

Analyze Historic Brick p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 12 o Provide flashing and weeps at lintels and interruptions in masonry o Repair roof flashings and gutters that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets, gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets, gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets and roof flashings that are part of the exterior wall construction p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 13

Building 128 o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets, gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair parapets, gutters and roof flashings that are part of the exterior wall construction p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 14 o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair gutters and roof flashings that are part of the exterior wall construction o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair gutters and roof flashings that are part of the exterior wall construction

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Building 340 o Tuck point existing deteriorated and failing mortar joints o Replace existing spalling and cracked brick with new or reclaimed brick to match existing brick in color, properties and texture.

o Repair or replace rusting door and window lintels as required o Provide flashing and weeps at lintels and interruptions in masonry o Repair gutters and roof flashings that are part of the exterior wall construction

4.0 GENERAL CONSIDERATIONS FOR MASONRY RESTORATION

4.1 General Comments

Preliminary Considerations: Masonry restoration and cleaning involve many considerations.

First, consider the reasons behind the decision to restore and clean masonry. If the only reason is appearance and the structure is not of historic significance, the work may require less attention, and economics may play a larger role in selecting cleaning procedures. If historic preservation is a reason, then evaluate the long-term effects of the restoration and cleaning to ensure that no harm will be done. Other considerations include the causes for deterioration, the current condition of existing masonry materials and construction, the source and composition of original materials, the extent and nature of earlier restoration work (if any), the availability of suitable materials for replacement and repair, and the limitations imposed by Project location, military procedures and protocalls and governing regulations.

Once preliminary decisions have been made, testing the effectiveness and safety of proposed procedures is the next step, unless previous experience with similar work offers sufficient assurance that testing is unnecessary. It is particularly important that tests be conducted to evaluate cleaning materials and methods. Unless the Project is small or the work can proceed on a cost-plus basis, it is generally necessary to have these preliminary tests performed under a separate contract. These tests should make it possible to ensure predictable results and to establish specification requirements that permit competitive bidding.

It is important to begin testing as soon as possible to allow time for additional testing and for the test areas to weather. If possible, allow enough time to pass after completing the tests to detect any undesirable long-term effects. A waiting period of one year is advantageous because it provides exposure to a full seasonal cycle, but 30 to 90 days is more practical and should be considered a minimum. Preserve and identify the sample test areas for examination by prospective bidders. Do not confuse this testing procedure with the mockups required in the “Quality Assurance” Article in the Specification. Those test areas primarily serve as a

Analyze Historic Brick p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 16 standard for judging the completed work but can also be used to determine which process to use if prebid testing is impractical.

Another preliminary consideration involves how detailed the Drawings will be and the extent of certain types of restoration and cleaning work. For some work, such as general cleaning and often repointing, it is frequently most cost-effective to require the Contractor to do such work to all masonry. For other types of work, such as crack repair, masonry unit replacement, special spot cleaning, and sometimes repointing, it is recommended that the Drawings indicate the extent of such work, or at least define a base bid quantity for all bidders. The Specifications should describe repair criteria for the work, or some means must be provided to decide the locations and possibly the extent of such work as the Project progresses.

Quantity allowances are one way of including such work in the Contract without deciding exactly where or under what circumstances the work will be required. A photo study to document existing conditions prior to repairs is also a good way to document existing conditions before construction begins. Unit prices are often used along with quantity allowances because the extent of work required will usually vary from that which is anticipated, when information is insufficient to determine exactly where the work is required.

Quantity allowances and unit prices generally encourage the Contractor to cooperate in determining the areas requiring this type of work. The tracking of actual repairs, compared to the original bid quantities, is also highly recommended to ensure that final contractual amounts are in line with original bid and unit price quantities for the additional repairs.

The method used to specify the extent of cleaning required is another consideration. One approach is to simply specify that masonry be cleaned. In this case, the Architect’s judgment determines how clean is clean, and the Contractor does whatever it takes to accomplish that degree of cleanliness. This approach may encourage the Contractor to use methods that can cause damage, and it may also require impossible results. Another method is to require that the cleaning match a previously prepared test sample or mockup; however, the test sample or mockup may not be representative of all the areas to be cleaned. A third approach is to use a prescriptive rather than a performance specification with the understanding that the results may not be exactly as expected but will be about as good as can be expected. With this method, the exact means and materials for general cleaning are specified, and additional spot cleaning is dealt with by Change Order or by using quantity allowances and unit prices.

4.2 Project Conditions

Protecting persons, property, and the environment can be a major concern when performing building restoration work, especially during cleaning operations involving chemicals or abrasives. Although the Sample Repair Specification includes performance requirements that leave the Contractor responsible for the particular methods of protection, there may be situations where specific methods should also be included and detailed by the specifier. This would be especially true if the building is used while the work is under way or if only certain methods of protection are acceptable to the Owner or to Authorities Having Jurisdiction

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(AHJ). Environmental considerations may limit the selection of cleaning methods and materials.

Air temperature is critical for cleaning operations and for repointing and repairing masonry.

When cleaning with water alone or with chemicals combined with water, the temperature should be above freezing, not only at the time of application but until the masonry dries out.

Freezing temperatures during this period can damage the masonry, so begin cleaning only when air temperatures are well above freezing and will remain so until cleaning is complete and masonry is thoroughly dry. The same restrictions apply to repair and repointing, except that repair and repointing could proceed if proper cold-weather construction practices are observed. Typical cold-weather construction practices include heating the mortar materials and covering the completed work with insulating blankets, or enclosing and heating the work area.

Sequencing and Scheduling: The example in the Sample Repair Specifications can be edited either to complete repointing before cleaning or to clean before raking out and pointing the joints. If their condition has deteriorated to the point where water from cleaning operations will penetrate deeply into the wall and cause damage, then repointing should be completed before cleaning, with enough time allowed for pointing mortar to harden. Otherwise, the normal process is to clean the masonry and then rake out and point the joints. Repair work should also precede pointing operations, particularly if new mortar joints are specified to be raked out and then pointed at the same time as existing joints.

4.3 Repointing Masonry

Identifying Problems: The need for repointing is usually related to some perceptible problem, such as open or eroded mortar joints, loose masonry units, or damp walls. The first step in a restoration project is to determine the causes of problems that need attention. If the reason for repointing is to stop water penetration, thoroughly investigate all possible sources of water. Damp walls may be caused by leaks from parapets, flashing, or roofs and such leaks may show up some distance below in masonry walls. Another source of water is rising capillary moisture (rising damp), which can cause dampness several feet above the ground. In either case, repointing the outer masonry wall will not solve the problem. Similarly, if open joints or loose masonry units are caused by foundation settlement or deteriorating materials, such structural problems should be corrected before beginning masonry work.

Recognize that repointing is an expensive and time-consuming task due to the large amount of handwork and special materials required.

Research: Repointing and repair work may involve analysis not only of mortar but also of masonry units and techniques originally used in striking the joints.

Mortar study or analysis is necessary if repointing mortar is to match the original in color, texture, and other qualities. Petrological examination of mortar is often used to determine the

Analyze Historic Brick p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 18 mineralogical makeup of mortar aggregates so they can be duplicated in the pointing mortar.

Mortar color can dramatically influence wall appearance. Different aggregates and dyes can be utilized to come close to a visual match to the old mortar materials.

Study pointing styles and methods of producing them. Examine both horizontal and vertical joints to determine which were struck first and whether they are the same style and color.

Some buildings, for example, have concave-tooled horizontal joints and flush-cut vertical joints stained to match the brick, creating the effect of horizontal bands. Also examine each of the building’s faces because the front may have a different pointing style than the other sides.

Study masonry units to ensure that replacements will match originals. Within a given wall, there may be a surprising range of colors, textures, and sizes. Replacement materials should match this range, if possible, rather than specific units. Consider potential sources of replacement materials early in the planning process to determine availability, cost, and delivery time. It may be possible to obtain suitable bricks from salvaged building materials suppliers or, if of comparable hardness and color, bricks may be moved from unexposed areas in the building to exposed areas.

Masonry Materials: Alternative requirements for replacement brick are included. One requires the Contractor to match existing materials and the other requires matching the Architect’s sample. The first assumes that replacement materials that match existing materials are readily available and easily discoverable by a masonry supplier. The second may indicate the unavailability of materials that closely match existing units and, therefore, the need to exercise more direct control over what is a satisfactory match. Matching existing stone trim and sill units may also be difficult or expensive. In certain instances, precast concrete, glass-fiber-reinforced cement, or glass-fiber-reinforced plastic units have been used as substitutes.

Properties of Mortar: In general, repointing mortars should match original mortar in composition and proportions as well as color and texture. The importance of matching the composition is frequently overlooked, yet the match is necessary if old and new mortars are to have the same physical characteristics. However, it may not be necessary to determine the exact physical and chemical characteristics of existing mortar if materials used in the new mortar produce the following results:

• A compressive strength that is less than the existing masonry units and equal to or less than original mortar.

• A color and texture matching the original mortar.

It may be important to define what is meant by original mortar if masonry has been repointed several times. In some instances, mortar with the wrong physical properties or appearance has been used. It is also important to stipulate whether the new mortar is to match the original in its original unweathered appearance or as it now exists. Attempting to match weathered

Analyze Historic Brick p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 19 mortar is unlikely to be effective because as the new matching mortar weathers, it will tend to develop a different appearance from that of the original mortar.

Stresses within a wall caused by expansion or contraction or by settlement must be accommodated in some way. In masonry walls without adequate expansion or control joints, these stresses should be relieved by mortar rather than brick. Mortar that is harder (less elastic) than masonry units (old bricks and newer Portland cement-based mortars) will not give, causing the brick to crack and spall. Uneven movement in masonry can also break the bond between mortar and brick, opening hairline cracks and allowing water penetration.

Porous mortar permits water within the wall to migrate and escape. Mortar with a high cement content does not permit this movement, and water trapped within the wall may be subjected to freeze-thaw cycles that can spall the brick.

Mortar workability or plasticity is also important. New mortar should have both cohesive and adhesive qualities to make physical contact with masonry and old mortar. It should have the maximum amount of sand consistent with such workability to help reduce shrinkage while setting. Also, new mortar must have good water retention to resist rapid loss of water through absorption by brick or old mortar while setting.

On new construction, mortar using sharp sand is advocated because the particles interlock and produce better shear strength and unconfined compressive strength than does rounded sand, just as crushed stone provides a more stable pavement base than does rounded gravel.

Sharp sand also requires less void space, which can reduce the volume of cementitious materials and produce less shrinkage. However, historic building repairs often include recommendations that aggregate with rounded edges be used. Usually mortar that matches historic mortar will require rounded aggregate because historic mortar is usually made with alluvial sand, which is rounded, and has the added benefit of improved workability.

A high-lime mortar is generally best for older restoration. High-lime mortar is softer, more elastic, and more porous and exhibits a lower volume change due to climatic conditions. Lime is also slightly soluble in water, which causes very small cracks to be self-healing. A slight amount of lime dissolves in rainwater and is precipitated at the crack during the drying process, thus sealing the crack. High-lime mortar will reduce potential stresses at the face of the masonry and will also help minimize shrinkage, which leads to hairline cracking.

However, under rare circumstances, some Portland cement may be added to improve strength or working properties. It is important however that a mix similar (or slightly lower) in strength be utilized in order to maintain the original properties and overall integrity of the wall. Testing existing mortar and matching is the best approach.

Although using proper materials and techniques will provide a watertight job, appearance is also important. Both color and texture of sand or other aggregates can influence the color and texture of mortar. Natural impurities found in some sands, such as natural metallic oxides or

Analyze Historic Brick p:\__projects\_sf08\hasf080415 selfridge brick analysis\_pmt\rpt\__ final report 02-09-09\report revised final submittal 03 11 2009.doc 20 clays stained with such oxides, can act as pigments in historic mortar. Every reasonable effort should be made to use these natural sources of color and texture in matching mortar.

Mortar texture also affects visual characteristics. Modern cements are finely ground and thus present a uniform texture and color. Early mortars did not use materials so finely ground however, and may have contained lumps of oyster shell or incompletely burned lime. The size, color and composition of these lumps should be determined as part of the mortar analysis, and they should be duplicated as closely as practicable in the repointing mortar.

Crushed oyster shells can be obtained from poultry supply dealers, and lime particles may be made by soaking quicklime, drying it, and screening it on the jobsite.

Joint Preparation: Generally, old mortar should be cut out to a minimum depth of 2 ½ times the joint width to ensure an adequate bond between new mortar and existing masonry. For joints less than 3/8 inch (10 mm) thick, cutting mortar back ½ inch (13 mm) is usually sufficient if mortar behind that location is in good condition. Loose and disintegrated mortar beyond this minimum depth should be carefully removed.

The use of power tools to remove existing mortar is discouraged because of likely damage to brick. Damage to the edges of brick will significantly affect the character of brickwork; also, water absorption is increased because the more porous internal make up of the brick is not protected by the hard-burned outer surface. Where joints are uniform and fairly wide and where bricks were machine made with straight edges, it may be possible to use a grinder for the horizontal joints. If bricks are fragile and mortar is hard, grinding may be necessary to prevent cracking due to the impact of the chisel. A test patch should establish the feasibility of using power tools. A circular saw should not be used even if power tools are allowed, because the blade guard obscures the view of the joint being removed. The grinding wheel (usually a diamond-impregnated metal blade) should be narrower than the joint and should be run down the center of the joint, then followed by hand removal of the remaining mortar. Small pneumatic impact chisels, such as those used for carving limestone, may also be useful in the hands of skilled workers. If there is any chance that masonry may be damaged, specify hand methods exclusively.

It is important to remove mortar cleanly from the brick, leaving square corners at the back of the cut. Before pointing is started, remove all loose particles from the joint using a stiff-fiber brush, low to medium pressurized water, or compressed air. Masonry and old mortar should be wetted when pointing, but no excess water should be present.

Mortar Preparation: Mortar should be thoroughly mixed to obtain uniformity of both visual and physical characteristics. Dry ingredients should be mixed before adding water. The mixture should be prehydrated to help prevent shrinkage on drying. To prehydrate mortar, sufficient water is added to the dry mix to make damp, stiff mortar; just damp enough to be squeezed into a ball with the hand. After one or two hours, mortar is remixed with additional water to reach the desired consistency.

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Antifreeze compounds are not recommended. Their effectiveness with high-lime mortar is questionable, and they may contain salts that can produce efflorescence.

Air-entraining agents are also discouraged. The air that these agents induce can have a detrimental effect on both bond and strength, and they are considered unnecessary in high-lime mortar because of its natural plasticity.

Bonding Agents: Using chemical agents to increase the bond of new mortar to old masonry should be avoided. Chemical agents are generally unnecessary and can be harmful. If the joint is correctly prepared and moistened before placing new mortar, and if new mortar is properly prepared and applied, there will be a good bond between new mortar and adjacent surfaces.

If chemical agents are used, there may be a tendency to neglect proper joint preparation on the assumption that the agent alone will produce an adequate bond. Deteriorated mortar or dirt in the joint will prevent the bonding agent from functioning properly. In addition, some of the agent may be smeared on the face of masonry and might be difficult to remove. This situation can especially occur on walls with thin mortar joints.

Pointing (Filling) Joints: Where existing mortar has been removed (or has fallen out) to a depth greater than that required by the joint width, the joint should be partially filled first, compacting mortar in several layers and bringing it out to the level of the remainder of the joints. Once this is done, the back of the remaining joint may be filled by applying a 1/4-inch to 3/8-inch (6- to 10-mm) layer of mortar. As soon as the applied mortar has reached thumbprint hardness, another layer may be applied. Several layers of about the same thickness are needed to fill the joint. Allow each layer to lose much of the free water and become stiff before the next layer is applied.

Pointing mortar can be applied to horizontal joints with a tuck-pointing trowel by pushing it into the joint from a hawk held in line with the bottom of the joint. The vertical joints are then filled by troweling mortar up from the hawk and into the joint. A cement finisher’s or plasterer’s trowel held upside down makes a suitable hawk since its thin blade can be inserted partly into the horizontal joint without getting in the way of the trowel. Another method for filling the joints is by using a canvas bag with a metal nozzle that is operated like a giant version of a cake decorating cone: The bag is squeezed and the mortar comes out the nozzle and into the joint. A mortar gun, which consists of a variable-speed electric drill driving an auger to feed mortar from a hopper into a nozzle, is made by a company that claims the gun is five times faster than the trowel method and uses mortar that is not watered down. With either the bag-and-nozzle method or the mortar gun method, each layer should be troweled or tooled immediately after being placed to compact it into the joint.

When the final layer of pointing mortar has reached thumbprint hardness, the joint is tooled to match the existing joints. If old bricks have worn, rounded edges, it is usually best to recess the final mortar surface slightly to avoid a visually wider joint and to avoid a thin featheredge that may be easily damaged and may admit water.

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“Aging” New Mortar: Even with the best efforts at matching original mortar color, texture, and materials, there will usually be visible differences between old work and new. If mortars have been properly matched, the best treatment is to let new mortar age naturally. However, surface treatments may be desired, despite the likelihood that aging may again reveal differences. Any treatment proposed should be carefully considered and tested first.

One possible treatment is light brushing with a stiff-fiber brush immediately after tooling.

This will roughen the surface slightly, producing a weathered look. Another treatment is a low-pressure water spray with a fine nozzle after tooling. This will wash away part of the cement and lime before they have fully hardened and leave the sand more exposed on the outer surface, just as in natural weathering. This procedure requires great skill and care, so it should not be specified unless experienced specialists are available to perform the work.

Another method is the application of manure, which releases organic acids that react with the lime and cement leaving more of the sand exposed. This method also hastens the soiling of the masonry and the establishment of microorganisms, which are both a part of the natural aging of masonry.

4.4 Cleaning Existing Masonry

Existing Conditions: Several considerations enter into the decision of whether or not and how to clean existing masonry. One is whether the primary purpose for cleaning is for a clean appearance or for masonry preservation. In some instances, the two purposes may coincide.

In others, they may conflict. To reconcile this matter and to decide on a suitable cleaning method, determine the nature and source of dirt or other substance appearing on masonry.

Also consider the effect various cleaning processes might have not only on masonry but on surrounding construction. With this information, an informed decision can be made.

Types of Cleaning: There are three major groups of cleaning processes: water, chemical, and mechanical (abrasive).

• Water methods soften the dirt and rinse the deposits from the surface. These methods are frequently slow since they rely heavily on soaking to soften the dirt. Pressure washing often speeds the process, but it is partly a mechanical method, relying on the abrasive action of the high-velocity water droplets.

• Chemical cleaners react with the dirt and masonry to hasten the removal process. The dirt, reaction products, and excess chemicals are then rinsed away with water.

Different chemical cleaners are used with various kinds of clay masonry units because some are more easily damaged by certain chemicals than others. Heated water increases the effectiveness of some chemical cleaners, especially alkaline detergents and paint removers.

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• Mechanical methods include abrasive blasting, grinding, and sanding that remove dirt by abrasion and are generally done wet to reduce dust problem. They are usually followed by a water rinse. Some methods use very soft abrasives, such as sodium bicarbonate, to minimize abrasion to the harder masonry; other use very fine, lightweight particles, such as ground corn husks or powdered aluminum silicate, with low-pressure compressed air to provide a scrubbing (or sanding) action rather than an impacting action. Although some mechanical methods may be suitable for use on porous masonry that might be harmed by large amounts of water or chemicals, most are patented proprietary processes. Mechanical methods are not included in this study.

Proprietary Methods: Patented methods for cleaning exterior masonry surfaces abound and are frequently touted by their inventors as the safest and most effective method. Most of these methods do possess advantages over other methods, but most also have their own problems, which are usually not pointed out in magazine articles written by their proponents, who usually have a financial stake in the method. Patented methods have been omitted from the Sample Repair Specification, not because of any skepticism about them but because one of the goals is to produce a specification that encourages competition. If interested in the various proprietary methods, research referenced related magazine articles and contact the companies offering them for additional information. Also verify methods owners, architects, conservators, and other who have had experience with the proprietary method in question before specifying it.

Testing Cleaning Methods: Several potential cleaning methods should be tested before selecting one for the Project. The simplest and least aggressive should be tried first, followed by progressively more aggressive methods until satisfactory results can be achieved without damaging masonry. The simplest methods are often effective, least expensive, and least dangerous.

Determine the level of cleanliness desired before selecting a cleaning process. Do not over clean a historic structure. A brand-new look is both inappropriate and only temporary, and the process used to obtain such a look may contribute to erosion of the surface, which should be preserved.

Cleaning tests, whether simple or complex, should be applied in an area of sufficient size to give a true indication of effectiveness. Remember that a single building may have several types of masonry materials with different finishes, each of which should be tested separately.

Test results may indicate that several cleaning methods should be used on a single building.

When feasible, test areas should be allowed to weather for an extended period before the final evaluation.

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4.5 Potential Cleaning Problems

Water cleaning methods require that all joints, including mortar and sealant, be sound enough to minimize water penetration to the interior. Porous masonry may absorb excess amounts of water during the cleaning process and cause damage within the wall or on interior surfaces.

Normally, however, water penetrates only partway through moderately absorbent masonry materials. Excess water can also bring soluble salts from within masonry to the surface, forming efflorescence.

Water methods cannot be used during cold weather because water within the masonry can freeze, causing spalling and cracking.

In spite of these potential problems, water methods are the simplest to carry out, the safest for the building, and the most economical. Detergents can be used to enhance water cleaning methods if necessary.

Chemical cleaning agents are often water based and have many of the problems of plain water, but they also have other problems. Some types of masonry are subject to direct attack by cleaning chemicals. Many contain hydrofluoric acid that will etch the glaze on terra cotta and glazed brick. Acid cleaners generally remove a slight amount of the mortar and possibly some of the masonry material along with the dirt, causing slight surface erosion. Chemical cleaners may also react with substances in masonry, causing a change of color or producing a hazy residue. Chemicals can also react with masonry and mortar materials to create soluble salts than can form efflorescence.

Mechanical cleaning abrades dirt off the surface of masonry rather than reacting with the dirt and masonry as in water and chemical cleaning methods. Since abrasives do not usually differentiate between dirt and masonry, some surface erosion is almost inevitable with mechanical methods, especially blasting. Although a skilled operator can minimize it, some erosion will still take place. For brick, however, even minimal erosion is unacceptable.

In most cases, abrasive blasting will leave minute pits on the masonry surface. This additional roughness actually increases the surface area on which new dirt can settle and with which pollutants can react.

Mortar joints, especially those with lime mortar, can also be eroded by mechanical cleaning. In some cases, the damage may be visual, such as loss of joint detail or increased joint shadows.

In other cases, erosion of the joint mortar may permit increased water penetration, creating a subsequent need for repointing.

4.6 Final Cleaning

If general cleaning is completed before masonry pointing, then it will be necessary to remove excess mortar left on the masonry face by a final cleaning operation. Most mortar can be easily

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