The outline of this two-part article of this case study follows below. Last week we discussed sections one and two, and today we are discussing sections three and four:
Brick DeteriorationOver the century following initial construction, small inadequately executed repairs attempted to address areas of substantial deterioration in the aged factory facade. Mismatched common bricks lacking the color and texture of the original faces were inserted in piecemeal fashion without consideration for holistic cohesion. Incompatible Portland cement-laden mortars, while strong in compression, were sloppily applied without awareness (or with disregard) of their detrimental effects upon softer historic bricks. In cases of improper restoration and repointing, as moisture penetrates through the permeable historic bricks but became trapped by dense modern mortars, cycles of damage from freeze-thaw action and salt crystallization will accelerate breakdown of the brick masonry wall system. By the late 20th century, facing obsolescence, the complex was converted into residential use, injecting extended longevity through adaptable renewal. However extensive facade remediation wasn’t considered a priority. It is imperative though, as weathering effects continue taking a toll on the distressed brick surfaces. While decorative details and styling inevitably evolve with changing styles, the fundamental requirement for a sound weather-tight shell should be considered central to stewardship of the overall facility. Pllanning for thorough repointing of the deteriorated historic mortar joints with suitable materials and craftsmanship befitting the aged bricks is essential. Mortar is a mixture of sand, lime, and water that is used to bind bricks and stone units together in masonry. The lime is typically calcium hydroxide (Ca(OH)2), which comes from heating limestone (calcium carbonate, CaCO3) in a process called calcination. Limestone can be found in nature in most parts of the world and limestone, along with tabby construction mortars (from lime-rich seashells) and binders have been made and used throughout the world for thousands of years. When lime mortar is first made, the calcium hydroxide dissociates into calcium (Ca2+) and hydroxide (OH-) ions when mixed with water. These ions interact with silicate compounds in the sand to form calcium silicate hydrates (CSH), which act as the primary binding agent in the mortar. The CSH compounds have a layered crystal structure and form strong bonds with the rough surfaces of the bricks, adhering them together. Over time though, the mortar begins to deteriorate through both physical and chemical processes. Physically, the expansion and contraction of bricks due to temperature changes exert stresses on the mortar. The mortar can also be worn down by wind, rain, and pollution. Chemically, the mortar degrades in several ways, such as carbonation, the process wherein calcium hydroxide reacts with atmospheric carbon dioxide, reforming calcium carbonate. This reaction removes the lime available to form CSH compounds, reducing the mortar’s strength at the outer face of the exterior brick face at a building facade, for example. It also results in volume reduction, cracking, and increased porosity. The interesting thing a out this chemical reactions is that the general shape of the mass of the mortar remaims somewhat intact, but the The chemical equation of the reaction can be expressed as follows. Ca(OH)2 + CO2 → CaCO3 + H2O
Ca(OH)2 + SO42- + 2H2O → CaSO4·2H2O (gypsum)
On a microscopic level, these deterioration processes disrupt the calcium silicate hydrate (CSH) bonds holding the mortar together. The layers of CSH crystals become fragmented and decalcified, weakening the interatomic forces between them. Intergranular cracks form within the mortar, expanding over time. The mortar slowly reverts to a loose, incoherent material (loose materials without bond between them) incapable of bonding the bricks. While all mortar deteriorates over time, modern Portland cement mortars tend to degrade differently than historic lime mortars. The lime mortars were more porous, allowing movement of moisture vapor that minimized stresses. The lime also re-crystallized over time, “healing” small cracks. Using compatible, historically accurate mortar mixes and repointing techniques can extend the service life of historic masonry buildings and preserve their appearance. Repointing and TuckpointingWhen Portland-based mortar is used for spot repointing repairs, the visual mismatch of color and texture further detracts from the wall’s character. But even more critically, the cementitious mortar’s inflexibility prevents seasonal expansion and contraction of the historic bricks. This leads to further cracking and deterioration. Using properly calibrated and mixed lime-rich mortar, matching original proportions and / or characteristics allows moisture exchange while accommodating the slight movements inherent to brickwork over decades. Modern Portland cement-based mortars cure through rapid hydration of the cement components to achieve high early strength and compressive resistance. However, Portland mortar lacks permeability, instead forming an impermeable barrier preventing passage of moisture. Salts and moisture then crystallize within the porous historic bricks, fracturing and decaying the brick faces through freeze-thaw mechanical pressures. The inflexibility of cured Portland mortar joints also resists the minute expansion and contraction of bricks over seasons, resulting in cracks as stresses accumulate between disparate materials. Harsh visual discontinuities also arise when the Portland mortar’s color and texture clashes against weathered historic bricks. Proper repointing focuses on preserving the aging facade in its imperfect, authentic state rather than imposing modern standards of uniformity. The process involves raking failed and deteriorated remnants of mortar from the joints to sound depths, retaining intact bricks. The new lime mortar replicating structural characteristics of historic mixes is installed and tooled to match original joint profiles. Often, damaged or missing bricks salvageable are repaired and reused; replacements attempt match old bricks in size, color and texture as close as possible. The goal is unified wall integrity and breathability, not a perfect appearance. Proactive masonry repointing restores eroded mortar to protect bricks, while halting deterioration and improving structural performance. Well-executed repointing can stabilize the weathered factory facade into its next century. We can HelpInfinity Design Solutions is a historic restoration specialist contractor specializing in both historic masonry restoration such as tuck pointing our repointing, and brick repair. If you have questions about the architectural details or facade of your historic building in Washington DC, reach out and say hello and if we can help we’ll be glad to assist you. You can email us or call us on the telephone at the following link: contact us here. <p>The post Old historic warehouse in great need of brick restoration – Part II of II first appeared on Infinity Design Solutions.</p> Via https://www.ids-dmv.com/masonry/old-historic-warehouse-in-great-need-of-brick-restoration-part-ii-of-ii/
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About UsInfinity Design Solutions LLC (IDS) is a full service general contracting company in the heart of the Dupont Circle neighborhood of Washington, DC. We focus on repair and renovation of buildings and facilities in both historic designated neighborhoods and the commercial-zoned central business district of the city. Follow Us
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