Butte CPR Preservation Pamphlet #1

Repointing and Maintaining Historic Brick in the Butte Area

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Details

Introduction/History

Construction of brick homes and commercial buildings in Butte began in earnest around 1880. Brick was preferred for its resistance to fire and signified permanence as Butte grew from a mining camp to a city.

Most brick used in Butte is called "common brick" a somewhat soft reddish orange brick that is easily damaged by water, abrasion, and impact. Prior to 1900 common brick was made by three to four small local firms in Butte. After 1900, most production shifted to Anaconda. High-quality hard-fired brick, commonly with a light yellowish color, was used in the more visible areas some of the more stately homes and buildings; common brick is typically found along the rear back and sides of the buildings. The higher quality brick was brought in from outside Butte; some came from the Kessler facility in Helena, but most likely came from out of state. As the last remaining manufacturer in Butte, Pioneer quit brick production in 1955.

Masonry and Mortar Overview

Function and dynamics of masonry

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Common brick is by far the most used brick in historic Butte buildings. A lower firing temperature makes common brick softer, less tolerant to high compressive stresses, and more permeable to water vapor than either historic higher quality brick or modern brick. Mortar is designed to be an expansion joint and vapor membrane around masonry blocks or brick. The mortar must be weaker and more permeable than the bricks. Since common brick is weaker and more permeable than modern brick, proper mortar must be substantially weaker and more permeable to water vapor than modern mortars, the mortar that is sold in pre-mixed bags.

The term "repointing" comes from the masonry term "point," which means to fill or refill and finish the joints of brickwork or stonework with mortar. Another term, "tuck pointing," a special type of repointing where the joints are made to appear smaller than they actually are, is commonly but incorrectly used to simply mean pointing or repointing.

Common problems

Water

Repeated wetting of brick surfaces by water is probably the most common reason for brick and mortar deterioration. Water running along the face of brick, seeping up from wet ground around a brick building, splashing onto the surface at the ground or at a roof surface, or repeatedly wetting the brick from wind-driven rain are common sources of brick repair and maintenance problems. Aside from wind-driven rain, most other sources of water damage should be corrected before beginning brick repair.

Paint

A large number of buildings have painted brick. Full restoration would involve paint removal from the brick. As a general rule of thumb it is not advisable to paint brick. This is not only true from the standpoint of preserving the structural integrity of the brick but also from a historical perspective. An application of paint or a waterproofer that is of the wrong type will prevent the brick from breathing. This causes water vapor pressure to build up in the brick, which can cause the entire face of the brick to pop off. Much of the exterior paint contains lead, so proper care must be taken to insure safe removal. The highest risk method of paint removal is dry abrasive blasting using sand, grit, or any other particulate. This method of paint removal is also the most damaging to the brick. The face of the brick is often totally destroyed during this type of removal process. Paint adheres less readily to sandy mortar than to the brick. Initial paint loss occurs on mortar joints and spreads. There is no completely safe method of removing lead paint during do-it-yourself renovations.

Mortar and Brick disintegration

Repeated wetting, freeze/thaw action, and water running down brick faces commonly erode mortar, especially from vertical joints. Properly pointed brick can be expected to be essentially maintenance-free for 50 to 75 years. The effects of normal mortar disintegration are most likely to be visible first on walls that are exposed to prevailing winds, commonly west-facing walls in Butte. In many cases, not only has the mortar decayed, but also select bricks may need to be replaced. Individual bricks are seen to disintegrate more rapidly than their neighbors due to manufacturing flaws in these bricks, damage from nails or impacts, or by localized deterioration by water. Whatever the cause, some damaged bricks will have to be replaced.

Brick firing techniques have varied considerably over time and place, so different locally made bricks can have somewhat different characters. At times some Montana retailers will offer used brick for sale.

Options for Repair

Do-it-yourself

Matching New Mortar to Old Mortar

A major portion of good workmanship in masonry patching or repointing involves carefully blended and matched masonry. Any masonry patch actually involves the process of repointing. It is uncommon for all joints in a building or a wall to require repointing. The most noticeable mark of a good job of repointing masonry is the ability of the repaired area to blend in with the surrounding brick. Although color and tooling style of the mortar surface are the most noticeable mismatches, the composition (hardness) of the mortar most critical to limit damage to the brick.

New mortar must match historic mortar in color, texture, and tooling. The sand must match the sand in the historic mortar. New mortar must have greater vapor permeability and be softer than the surrounding brick.

Colored premixed patching compounds are formulated specifically for patching masonry on historic homes and are available from several manufacturers. Cement, sand, latex (local term may be moose milk) and coloring are locally available.

Components of mortar

Historic mortars are made up mostly of clean, washed sand and lime, with either no or a small amount of Portland cement.

Sand: Sand is the largest single mortar ingredient in mortar. Sand is generally mixed with the binder (cement/lime combination) in a 1:3 binder to sand ratio. Sand composition affects color and texture. Most sand in the Butte area comes from weathered granite that surrounds the valley. Inspection of sand in the existing mortar should give a good idea of the composition, range in grain-size, and angularity of grains. Much of the mortar sand available at commercial concrete yards should match the sand in most mortars.

Lime: Calcium hydroxide, lime or hydrated calcium oxide lime, is the dominant binder in historic mortar. The lime mortars are more permeable than denser Portland-cement-rich mortars. Historical mortar served to function more as a bedding material and an expansion joint than as a glue between bricks. The large amount of lime in the mortar allowed moisture to pass through it more readily than the brick.

Lime mortar is soft, porous, and changes little in volume due to temperature fluctuations, and makes the mortar easy to work with when wet. These qualities make high-lime mortar a consideration for any repointing job when quick set is not a priority. Lime should conform to Type S, or Type SA, Hydrated Lime for masonry purposes. Although high-lime mortars are less resistant to erosion than Portland cement mortars, the soluble nature of the lime makes these mortars self-sealing, that is small cracks and gaps are filled during wetting and drying cycles.

Portland Cement: Portland cement is a fast-curing, hard, silica and lime-based material that can harden under water. Portland cement was not in common use throughout the country until the early 20th century and was considered primarily a minor additive to mortars. This is a fast-curing, high strength, additive to mortar that helps accelerate mortar set time and ultimate strength. With the availability of stronger bricks by the 1930s, most masons used a mix of equal parts Portland cement and lime. Thus, the mortar found in masonry structures built between 1873 and 1930 can range from pure lime and sand mixes to a wide variety of lime, Portland cement, and sand combinations. While the earliest mortar mixes contained no cement, it is unclear how much was used in most buildings in Butte. Most Portland cement is the common, gray type. White Portland cement is available from masonry supply stores and is preferred over the gray type when trying to match mortar color. Use of the gray type imparts a grayish color to mortar that may or may not be acceptable. The white type can be more easily colored using pigments.

Masonry Cement: Masonry cement is a pre-blended mortar mix commonly found at hardware and home repair stores. It produces mortars with high compressive strengths that are appropriate for strong stone or modern, hard bricks. The mortar is inappropriate for, and can damage, historic masonry.

Pigments: Some historic mortars contained pigments to match or contrast with the brick or stone. Red, brown, and black pigments were commonly used but many were not stable, which resulted in color fading over time. Each of these has modern counterparts, which are readily available, colorfast, pure mineral oxides, and are generally acceptable as substitutes.

Replacing mortar

Repointing projects may consist of an entire building, single walls, portions of walls, or just a few joints. Only rarely will every joint need repointing. Commonly some brick replacement is needed. Sometimes poor joint profile traps water and accelerates mortar deterioration, and one may purposely choose a new joint profile. At other times, if the bricks have weathered rounded edges, mortar may have to be recessed to prevent the appearance of wider joints than the rest of the structure.

Procedures

Assessment

Mortar and brick deterioration should first be assessed. The degree of repointing will depend on the amount of mortar and the number of bricks that have deteriorated. Generally, if mortar can be scraped out easily with light abrasion by a metal probe, those bricks must be repointed. In some cases vertical joints may be more deteriorated than horizontal joints. Pay particular attention to areas that have been subject to running or standing water.

Spalling and severely rounded bricks should be considered for replacement. However, one must be careful to not get carried away, it's useful to assess the general condition of bricks on a surface and only replace those that are severely damaged, as compared to the others.

Because techniques will improve dramatically with practice, do-it-yourselfers should begin in areas with low visibility. Any problems that may creep up may be tackled in that spot, before there is a visual difference in a prominent area.

Mortar-Joint Preparation

Mortar joints near areas with missing mortar or any disintegrated mortar should be cleaned out to a minimum depth of 2 to 2-1/2 times the width of the joint, which is typically about a depth of ½ to 1 inch between most bricks. Stone masonry may require removal depths of up to several inches. All mortar that is easily removed should be removed, no matter the depth.

Because common brick is so easily damaged, some insist that the only safe means to remove mortar is by scraping and gentle hammering with hand tools. If strong hammering is required at the surface, the mortar may simply not need to be replaced. Judicious application of power tools can save time and may prevent joints by being loosened and bricks damaged by reducing the use of a hammer and cold chisel. Old screwdrivers of various widths make good tools to manually scrape deteriorated mortar from horizontal and vertical joints. It is possible to safely use a small hand-held grinder to remove mortar from horizontal joints. Use the grinder with a thin masonry or, preferably diamond blade, to grind a slot down the center of the horizontal joints. Use a hammer and a cold chisel to break away mortar on either side of the slot. Break the mortar off towards the joint's center until the correct depth is reached. Small pneumatic-powered chisels can also be used to knock out historic mortar without too much risk of damage to the brick. Prior to placing mortar the surface and all joints should be blown out with compressed air to remove loose particles and dirt. A precautionary particle filter mask should be worn.

Recipe for Mortar

Trial batches of mortar should be made in order to match the color, texture, and strength of existing mortar on a building. The following recipe can be used as a starting point for trials. Different coloring agents are available for nominal costs from masonry supply stores. Recipes can be scaled down for test batches, but keep clear notes of the different mixtures and carefully follow the recipe for each batch once a proper mixture is determined.

Experience will show how much mortar you can mix up and use at one time. The amount of mortar used in the 1-1½ hour time it takes to dry can increase greatly if brick replacement is being done.

Ingredients for a typical batch that will last for ~1 hour with examples of brand and price:

1 cup white Portland cement (Lehigh type 1 white Portland cement 94 lb ~$25-45)
3 cups Type S Lime (Chemstar 30-50lb ~$7-10)
6 cups sand (mortar or "brick" sand from concrete yard that has about the same mineralogy and size as historic sand in a building, ~$2-5 for 200 lb)
2 level teaspoons dark brown coloring agent (~$2 per lb)

Mixing:

Dry ingredients should be thoroughly mixed before adding clear, cold water. Water added to the above mixture is about 2-3 cups, with the last 1/3 of the liquid added very slowly with complete mixing in order to attain a somewhat dry consistency that will hold together when compressed. Small additions of water can turn a too-dry mixture into a too-wet mixture very rapidly. The mixture is kept in a solid ball in the bucket so as to reduce drying.

Repointing

If possible, work should be done in the shade so mortar will not dry too quickly. Freezing temperatures should be avoided while the mortar is drying and hardening. The mortar joint and adjoining masonry should be lightly wetted prior to repointing to avoid suction of the water from the hardening mortar. Mortar can be held in a bucket, on a masonry "hawk", or in a masonry bag. The best application of historic mortar is done by packing the joints with a somewhat dry mortar using a hawk and masonry trowel. Mortar is placed on the hawk and tamped into a sheet somewhat thinner than the joint. Pieces of mortar are then cut off the sheet and scraped into the joints using the trowel and hands. Begin by applying mortar to the deeper spots first. For these spots mortar should be added in layers not to exceed ¼ inch thick. Physically packing each of the layers into the joint with a repointing trowel makes for a strong bonded joint that is less likely to crack upon drying. The surface of the mortar is commonly within 1/8' to ¼" of the brick surface. However, if the bricks have weathered rounded edges, bringing this close to the brick surface may make the repointed joints appear far too wide. Joints may have to be recessed on weathered bricks in order to maintain an even appearance of joint width. When the final layer of mortar is thumbprint hard, now is the time to tool the joint surface.

Joint profiles are mostly concave, flat, or slanted up or down. If there is no original profile showing on the building one is free to choose his or her own joint profile. Sometimes poor joint profiles accelerate mortar deterioration by causing water to collect on the tops of bricks. Finishing off the joints is commonly done with a rounded "striking tool" or the flat part of a pointing trowel.

Brick Replacement

Brick removal must be done either for replacement or when the mortar has deteriorated to the point of loosening the brick from its neighbors. If mortar has completely deteriorated, multiple bricks will likely need removal and rebedding. If the brick is a veneer over a wood building, metal ties between the brick and wood sheathing and deteriorated tar paper will likely need to be replaced also. Individual spalled bricks can be difficult to remove without disturbing nearby sound bricks. Use of an angle grinder or a reciprocating saw with an abrasive blade can successfully be used to cut out mortar joints around bricks without the jarring forces involved in hammering and chiseling.

Bricks can be rebedded by placing mortar on the dampened bricks. A string, level, and straightedge may be useful in making sure the newly bedded bricks are in line with the existing wall. Coat the brick with mortar. Mix enough mortar to thoroughly coat the mating surfaces of the replacement brick, a process called buttering. Fill the joints. Force more mortar into the joints as needed (some will likely fall off), and then tool the seams to blend in the repair.

Cleanup

If mortar is spilled onto or ground into the faces of bricks, it must be removed to prevent staining. As the mortar dries and hardens, it becomes more difficult to remove. When joints are sufficiently dry, the faces of bricks may be scrubbed and rinsed with clean water with a rough rag, such as a piece of pile carpet. Care must be used so as to not disturb the finished joints. Muritic acid may be used carefully to dissolve dried and hardened mortar. With practice and skill, the need for brick cleaning is minimal.

Supplies and Equipment

Replacement Bricks

Common brick is not produced in our region so replacements must be found from recycled brick from another structure. The Archie Bray Foundation in Helena is scheduling plans on reopening brick production at the original site of Western Brick Works (originally Kessler Brick). Plans call for beginning initial production with a paving brick, but limited production of common brick may begin in the future.

Unfortunately for a person in need of matching up brick, there are usually no easy solutions. At times some Montana retailers will offer used brick for sale. Brickyards in neighboring states produce a product called "new used brick". These bricks are attractive and fired to the correct size but because of higher firing temperatures they cannot attain as deep an orange color as actual used brick has. This is a popular style of brick and many sources may have some of this style of brick for sale.

Good used (recycled) brick is sometimes available from local sources. Sometimes brick can be moved from unnoticeable locations on the dwelling itself, such as from attics, crawl spaces, porches, and similar concealed or semi-concealed locations, and replaced by modern materials. Only use bricks that have remained relatively dry and stable, as the color may vary from the original.

Tools

Necessary tools for own work:

Pointing trowel(s) of appropriate size: ¼", 5/16", 3/8" are common; stiff flex is useful for packing mortar into joints.
Hawk, a square, flat metal pan with a handle below for holding mortar.
Chisel(s) for old mortar removal (broken screwdrivers from home or pawn shop work well)
Gloves
Water spray bottle
Square edging trowel for mixing & serving mortar to the hawk
Bucket for mixing; 2-5 gallon hard-plastic bucket with a wire handle is ideal.
Old rug scraps, natural bristle brush for clean up

Useful Tools:

Low speed (~300-500 rpm) ½" drill for mixing mortar.
"Mud paddle" mixer attachment for drill.
4-5" electric hand grinder for cutting horizontal joints; bricks are easily notched and damaged if the tool is used on narrow joints or vertical joints; extreme care is required.
Diamond blade for grinder.
Safety equipment: face shield, dust mask, ear protection.
Compressor and air hose for cleaning out mortar.
Circular saw with masonry blade and jig to hold bricks for cutting, or brick-cutting table saw; half or partial bricks are typically needed around openings in walls; trimming bricks by scoring and splitting with a chisel is typically very inaccurate and wasteful.

Water Repellents

Recent innovation has led to development of products that can safely be applied to common brick to increase water repellency from, and consolidate damaged, brick faces. These products are silane-based liquids that are sprayed onto exterior brickwork and cured mortar. The water- or solvent-based liquids contain products penetrate into porous masonry, bonding weakened surfaces and form a semi-permeable coating that repels liquid water, but allows vapor to pass. By use of these products, building owners can reduce deterioration of partially damaged brickwork.

Hiring a contractor

Building owners should be aware that repointing a brick structure can be very expensive in time and or money. A job correctly should match the color and texture of the existing structure, and the composition of the mortar should not damage the brick. Experienced, knowledgeable contractors exist and should be sought out. Contractors inexperienced in repointing historic masonry should be eliminated based on questioning and evaluation of previous work. Good preparation and proper materials are crucial to long-lasting work. Expect to pay more than the lowest bid made.

Further Information

Sources of Information:

Cleaners and Silane-based water protection sealers:
Chemrex Inc.
Prosoco Inc.

Companies involved in Historic Masonry Preservation:
U.S. Heritage

National Park Service Preservation Briefs:
Available for purchase or some are downloadable as PDF files

Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings. Robert C. Mack, FAIA, and John P. Speweik. Provides general guidance on appropriate materials and methods for repointing historic masonry buildings. This publication revises the 1980 edition of Preservation Briefs 2: Repointing Mortar Joints in Historic Brick Buildings. The new PB#2 includes guidance for all types of historic masonry. 16 pages. 36 illustrations. 1998. GPO stock number: 024-005-01192-7. $2.00 per copy.

Others:

Preservation Brief 6: Dangers of Abrasive Cleaning to Historic Buildings. Preservation Brief 15: Preservation of Historic Concrete: Problems and General Approaches. Preservation Brief 38: Removing Graffiti from Historic Masonry Preservation Briefs 42: The Maintenance, Repair, and Replacement of Historic Cast Stone.

Bibliography

Quivik, Fredric L. 1985. The Western Clay Manufacturing Company: An Historical Analysis of the Plant and Its Development. Butte, Montana: Renewable Technologies, Inc.

Masonry Resources

Pioneer Concrete & Fuel, Inc., 825 Maryland Ave., Butte. 723-5435 (mortar supplies, tools, and cleaners and silane-based water protection sealers)

Archie Bray Foundation. Chip Clausen. Address: 2915 Country Club Avenue. Web Site: www.archiebray.org.

Smitty's Fireplace Shop Inc. (Smitty) Phone: 1-406-442-2242. Address: 4373 N. Montana, Butte.

U. S. Department of the Interior, National Park Service, Cultural Resources. Preservation Brief 2: Repointing Mortar Joints in Historic Masonry Buildings, by Robert C. Mack, FAIA, and John P Spewelk.

Haney, Craig K., 2001. "Restoration of Historic Brick Masonry." The Construction Specifier (March): 37-44.

Selected Reading

Ashurst, John & Nicola. Practical Building Conservation. Vol. 3: Mortars, Plasters and Renders. New York: Halted Press, a Division of John Wiley & Sons, Inc., 1988.

Cliver, E. Blaine. "Tests for the Analysis of Mortar Samples." Bulletin of the Association for Preservation Technology. Vol. 6, No. 1 (1974), pp.68-73.

Coney, William B., AIA. Masonry Repointing of Twentieth-Century Buildings. Illinois Preservation Series. Number 10. Springfield, IL: Division of Preservation Services, Illinois Historic Preservation Agency, 1989.

Davidson, J.I. " Masonry Mortar." Canadian Building Digest. CBD 163. Ottawa, ONT: Division of Building Research, National Research Council of Canada, 1974.

Ferro, Maximillian L., AIA, RIBA. "The Russack System for Brick and Mortar Description: A field Method for Assessing Masonry Hardness." Technology and Conservation. Vol. 5, No. 2 (summer 1980), pp 32-35.

Speweik, John P. "Repointing Right: Why Using Modern Mortar Can Damage a Historic House." Old -House Journal. Vol. XXV, No. 4 (July-August 1997), pp.46-51.

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