Brick maintenance and repair for historic and landmark structures

by Katie Daniel | October 21, 2015 11:40 am

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By Arthur L. Sanders, AIA
Durability is a hallmark of brick masonry construction, but even time-tested materials require maintenance to ensure a long life. Managing a property listed on the Canadian Register of Historic Places or a protected historic resource may also mean negotiating conservation standards, treatment guidelines, provincial or municipal regulatory restrictions, and community interests when considering how best to remediate deteriorating masonry. With all these considerations, even a quality brick structure can feel more like a liability than an asset. With the right strategy, however, masonry repairs need not overwhelm your schedule or budget.

Coupling restoration strategies with contemporary technology, a qualified design professional can develop a rehabilitation and maintenance plan that accommodates individual financial, technical, and aesthetic considerations. While deteriorated brick and mortar mean repairs, addressing the problem today will mitigate large-scale remediation tomorrow.

A successful project begins with a design professional who has demonstrated expertise in historic masonry restoration and specialized knowledge of early building techniques. It is important to consult with owners of historic buildings in the area, and with local preservation offices and industry organizations, to identify architects or engineers who have a proven track record with similar projects. Literature should be requested that describes qualifications and experience from any firms under consideration. Having a qualified mason and/or restoration contractor is also vital to a historically sensitive renovation, as there are many examples of historic masonry that has been ruined by poor judgement on the part of the person performing the work. Once the design professional has been selected, he or she can recommend masons and contractors with whom they have worked before.

The first step
Periodic comprehensive surveys of the building’s exterior should be the foundation of any routine maintenance and repair plan. This means that maintenance personnel should familiarize themselves with the properties and expected performance of the exterior wall materials. Specifically, they should look for the following indications brick masonry may be in need of maintenance or repair:

• efflorescence (i.e. a powdery residue on the brick surface that results from water-soluble salt deposits);
• spalling (i.e. missing or loose pieces of brick face);
• mortar joint deterioration (specifically mortar that has softened, broken apart, or cracked);
• loose, cracked, or displaced bricks;
• visible moisture damage (building interior or exterior); and
• mould or plant growth on masonry surfaces.

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Early investigation into these conditions can prevent more costly future repairs. For example, small cracks in mortar can allow water to penetrate the joint. With each freeze-thaw cycle, the mortar further deteriorates, allowing more water to enter the wall system, further compounding the problem. Eventually, the mortar falls out, leaving loose (and possibly dangerous) brick. Thus, addressing seemingly minor issues is important for preventing the development of critical problems.

In the case of water infiltration, the apparent cause may be but one effect of the problem’s true source. For instance, the symptom may be deteriorating mortar, but the cause could actually be improperly installed copings or flashings or even a leaky roof—either of which could allow water to enter the wall system. Here, an experienced design professional can help the owner avoid another costly repair job in the future by correctly diagnosing the underlying problem.

A thorough investigation
Why do brick and mortar deteriorate? Some contributing factors design professionals frequently look for include:

• excess moisture penetration at joints;
• weathering, including exposure to successive freeze-thaw cycles;
• contemporary conditions, such as pollution, not considered in the original building design;
• uneven settlement of the building foundation;
• thermal movement of masonry, especially at parapets;
• unequal expansion/contraction of the face masonry with the backup (this can include re-anchored face brick when improper anchorage is used); and
• capillary action causing rising dampness (water drawn into the building materials from the ground up).

Often, a combination of factors may be the culprit in masonry deterioration. For a repair or maintenance effort to achieve lasting success, the plan must address underlying conditions before other repairs are initiated. Preventive measures should also be included in the overall action plan to limit or slow future deterioration.

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With historic or landmark structures, special considerations may arise during the investigation. In order to avoid high-cost change orders and delays caused by unforeseen conditions, the design professional may need to research original construction documents and records of earlier repairs and building alterations. Onsite observations complement this evaluation, as portions of the original documents may be unavailable, and building construction can deviate from that shown on plans. Test cuts, probes, photographs, and laboratory analysis may be part of this investigation.

If the building is a Canadian Register property, provincial or municipal heritage site, or significant landmark, accepted treatment practices—such as those found in The Standards and Guidelines for the Conservation of Historic Places in Canada—must be addressed as early as possible in the project. If approval from the local authority having jurisdiction (AHJ) over historic properties is required, the process can take time, so the design professional should research the necessary codes and regulations and initiate the process of obtaining required variances and endorsements during the initial investigatory phase.

Once conservation standards and regulations have been taken into account, probable causes have been considered, and drawings and construction documents have been examined, a brick rehabilitation and maintenance program can be designed to meet the needs of a historic or landmark building. Generally, this includes establishing a scope of work, phasing, and budgeting.

Organizing the work
In undertaking a brick repair, replacement, or repointing project, the job must be planned carefully and logically. Stabilizing the structure is the priority. Any hazardous conditions identified during the investigation, especially those posing a danger to public safety, should be addressed immediately. Loose or severely deteriorated brick must be removed or held in place to prevent accidents.

Any such stabilization measures, however, should lay the groundwork for the rehabilitation effort. Care must be taken not to harm the structure or to increase costs of subsequent work. For instance, it is common practice to secure dangerously loose brick with netting or screening until a more permanent solution can be implemented. However, if improper anchorage was used in previous construction, removal may be sufficiently difficult as to further damage the building envelope.

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Prior to the start of masonry remediation, underlying causes of water penetration must be uncovered and corrected, or the work done will waste time and money. The mason should be skilled enough to provide commentary on discovered site conditions that may not have been apparent from the design professional’s observations. Proper sequencing can also help ensure both new and existing mortar weather similarly for better matching.

If budgeting allows, it makes economic sense to do all needed repairs at the same time to avoid incurring additional set-up costs. Scaffolding, sidewalk bridging, and other protective measures are expensive to take down and resurrect, and tenants will experience less disruption with only one construction period. Ideally, related roof and structural repairs should take advantage of scaffolding erected for brick work.

In larger projects, correct phasing is essential to avoid damage to newly repaired sections when preparing the next portion of the work. For example, if cleaning is part of the program and the mortar joints are watertight, it makes sense to postpone repointing until after the building is cleaned. For cases where mortar is eroded badly enough to allow water penetration, repointing would need to be completed first.

A prime consideration in planning the repointing or replacement phase of a masonry rehabilitation project is the weather. Masonry surface temperatures should remain fairly moderate, so beginning the work in very cold or very hot, dry weather is not advisable.

Without detailed and exacting construction documents, there is no assurance the often extensive time required to prepare and restore historic brick structures will be well-spent. Skilled hand labour and custom mortar mixes may be needed to appropriately repoint or rebuild deteriorated masonry. While a thorough investigation is essential to identify underlying problems and prioritize repair work, only specific construction documents and drawings can provide details of proposed solutions. Onsite project representation and construction administration can then help ensure the brick rehabilitation program is being implemented as designed.

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Quick fix?
Repointing, repair, rebuilding, and replacement of brick masonry on a historic or landmark structure can be time-consuming, noisy, dust-producing work, with scaffolding covering the building façade for some time. It can be tempting to look for a fast, easy solution. Once the investigation survey report identifies problem sites, Band-Aid repairs such as application of water-repellant coatings might seem to take care of the problem. While relatively breathable, these coatings can trap enough moisture within the brick to cause spalling. Once failures occur as a result of a quick fix, what seemed like a cost-saving repair may turn out to be the more expensive approach in the long run. If the building is designed for mortar, it is best to stick with mortar.

When moisture does find its way behind brick masonry, it can work its way out through mortar joints. Properly designed brick masonry walls get wet and dry out. However, if the joint is sealed, the trapped water will further break down the masonry, while the sealer hides this ongoing deterioration.

The investigation phase of a historic or landmark brick rehabilitation project may be longer than with modern construction, but this extra time is essential to uncover the root cause of the deterioration. Once the source problem is addressed, repair of the masonry may be a time-consuming and exacting process; replacement mortar and brick must visually match the original yet be resilient enough for contemporary conditions.

Is all this extra time and effort necessary? If done well, masonry rehabilitation can restore the structural and aesthetic character of a building. If done improperly, a repair project can not only detract from the building’s appearance, it can cause lasting harm to the masonry.

Conclusion
While brick rehabilitation on a historic or landmark structure can be disruptive, the investment in proper techniques and materials, along with skilled and experienced labour, means longer-lasting solutions with minimal maintenance work on the horizon. A qualified design professional who understands the special problems found in older buildings can act as the building owner’s or manager’s advocate throughout the rehabilitation process. Though it may not be a ‘quick fix,’ a thoroughly researched and exactingly executed remediation program can ensure that budget and design objectives are satisfied, with minimal disruption to occupants and as efficient a schedule as possible.

Shortcuts and inexpertly conceived repairs not only diminish a historic or landmark building’s esthetic character, but they can also actually exacerbate deterioration—this means more repairs. With careful maintenance, mortar joints can last many years, even 50 or more. A well-designed restoration project now can help to preserve the integrity of the entire structure later.

MASONRY REPOINTING PRIMER

[5] Repointing, also called ‘pointing’ or ‘tuck pointing,’ is the process of removing deteriorated mortar from joints and replacing it with new mortar. When to repoint Some indications repointing is necessary include: eroded mortar (6.4 mm [¼ in.] or more from the masonry face); crumbled mortar; hairline cracks; and broken bond between mortar and masonry. Repointing should be done only after underlying issues, such as leaking roofs, differential settlement of the building, unmitigated weather exposure, or rising capillary moisture have been addressed. Otherwise, the problem will soon recur, wasting time and money on multiple repairs. Examining the pointing style To maintain the esthetic quality of a historic or landmark building, it is necessary to examine the original techniques used in masonry construction. Pointing styles on both horizontal and vertical joints must be carefully noted, as these may differ, as might those on the different façades. Replicating original techniques as closely as possible will minimize visual discrepancies between newly repointed sections and those with original mortar intact. Preparing the joint Old mortar should be removed to a depth of at least twice the joint width, or until sound mortar is reached. In historic structures with thin mortar joints, the power tools typically used for this purpose can damage the masonry units by overcutting. Hand chisels and, when necessary, small pneumatic grinders, present the least threat to masonry units. Loose mortar must then be flushed or brushed from the joint. Preparing the mortar Repointing mortar should be carefully selected and properly proportioned. Where possible, the original mortar components and proportions should be duplicated. It is helpful to examine existing mortar which has not been exposed to weather, and then to match colour and texture using several preparations which have been allowed to dry. When specifying a repointing mortar mix, architects look not only to create a uniform appearance between original and newly repointed wall sections, but also to select a mortar that will perform well over time. High-cement mortars do not have the flexibility and waterproofing quality of higher-lime mortars; mortar that is too hard could cause the brick to spall at the edge if movement occurs. Ideally, mortar should look like the original, but be sufficiently yielding that hairline cracks become virtually self-sealing. Filling the joint Once mortar has been selected and the joint prepared, mortar should be pre-hydrated and then packed into the joint in thin layers. As most mortar shrinkage occurs during the hardening process, allowing each layer time to harden before the next is applied minimizes overall shrinkage. Tooling the joint When mortar is firm, joints should be tooled to the original profile. This is especially important when only portions of a wall area are to be repointed. If old bricks have worn, rounded edges, it is best to recess the final mortar slightly from the brick face. Not only does this treatment keep new joints from appearing wider than existing ones, but it also avoids creating thin featheredges that can break off easily and so admit water. Cleaning Once the mortar has dried, but not yet fully set, a stiff nylon or natural bristle brush may be used to remove excess mortar (metal bristles should be avoided with historic brick structures). If further cleaning is required, plain water is best, as chemical cleaners can damage masonry when not used properly. Repointed joints are particularly susceptible, because they do not fully cure for months. Washing with water before and after the use of chemical cleaners can help to avoid damage.

 

[6]Arthur L. Sanders, AIA, is the senior vice-president and director of architecture with Hoffmann Architects Inc., an architecture and engineering firm specializing in the rehabilitation of building exteriors. As director of the firm’s Connecticut office, he oversees a wide spectrum of historic and landmark rehabilitative work. Sanders can be reached via e-mail at a.sanders@hoffarch.com[7].

Source URL: https://www.constructioncanada.net/brick-maintenance-and-repair-for-historic-and-landmark-structures/

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