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Guidelines for Masonry Components
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Conservation Actions
Cleaning Masonry | Other Surface Treatments |
Repairing Masonry Elements
Re-pointing |
Re-setting Loose Masonry Units |
Pin and Glue Repairs
Dutchman Repairs |
Stone Consolidation
Local Replacement of Masonry Units |
Dismantling and Rebuilding
General Approach
| Recommended
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Not Recommended
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| Determine the cause of the distress, damage, or deterioration of the masonry component requiring repair through investigation, analysis, monitoring, and testing as required.
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Initiating a repair without understanding the cause of the problem being treated.
Carrying out a repair that does not address the cause of the problem.
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| Monitor the activity of significant cracks, bulges, tilting, or other deformations in masonry assemblies to help determine if repairs are necessary, including checking for: seasonal opening and closing of cracks; growth in crack length or outward displacement of bulges, over time; the appearance of new cracks or deformations, and increased rate of growth in bulges or deformation. |
Repairing cracks or deformations in masonry assemblies without first determining the cause or significance of the symptom of distress.
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| Prevent water from collecting within masonry assemblies by maintaining drainage at the base of the masonry, and by re-pointing deteriorated mortar joints.
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Applying water-repellent coatings to masonry surfaces that could trap moisture within the assembly.
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Conservation Actions
Cleaning Masonry
| Recommended
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Not Recommended
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| Clean using the gentlest methods possible and only when necessary to halt deterioration or remove heavy soiling or graffiti. Remove any vegetation or organic growths that are growing in or on the masonry using the gentlest means possible, such as soaking with low-pressure water (less than 350 kPa [50 psi]) followed by gentle scrubbing with natural bristle brushes, or scraping with soft plastic or wood spatulas.
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Using tools that could damage masonry to remove vegetative growth, including: steel wire brushes; metal spatulas, knives, or screwdrivers; abrasive pads such as steel wool; rotary grinders or sanders.
Using biocides to kill off plants such as lichens, as chemicals in the biocide may adversely react with materials on the Cenotaph/Monument, or be hazardous to non-target animals and plant life.
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Using flame cleaning to burn off plants such as lichens, as the excessive heat may damage the masonry or other materials on the Cenotaph/Monument such as wood, lead, synthetic caulks. |
| Remove stains or accumulated dirt on masonry, using low pressure soaking with water (less than 350 kPa [50 psi]) followed by gentle scrubbing with natural bristle brushes. |
Cleaning with water when there is any possibility of freezing temperatures.
Using detergents or household cleaners with Sodium Hydroxide (NaOH) to remove stains, as they may adversely react with the masonry or be hazardous to animals and plant life.
Using abrasive sandblasting techniques that can damage the masonry by eroding its surface, and can damage soft or delicate materials that form nearby parts of the Cenotaph/Monument.
Using high-pressure water cleaning methods (greater than 2700 kPa [400 psi]) that could damage the masonry, the mortar joints, and other soft or delicate components of the Cenotaph/Monument. |
| Clean granite using moderate-pressure water (maximum 2700 kPa [400 psi]) if soaking with water and scrubbing with natural bristle brushes does not provide an acceptable degree of removal. Use a fan type tip on the water pressure machine with minimum 375 mm [15 inch] spread. Do not hold the nozzle closer than 450 mm [18 inch] to the surface being cleaned. Hold the nozzle perpendicular to the surface. |
Using moderate-pressure water cleaning techniques on granite that includes lead-filled inscriptions.
Using moderate-pressure water cleaning techniques on granite masonry assemblies constructed with soft or poor condition mortars.
Using moderate-pressure water cleaning techniques on softer, less durable stones and brick, such as sandstone, marble, or limestone.
Adding detergents, acids, or other additives to the water when pressure washing. |
| Carry out cleaning tests to determine other appropriate cleaning approaches, if cleaning using low-pressure water and brushes or moderate-pressure water does not provide a sufficient degree of removal. Cleaning tests should be observed over a sufficient period of time so that both the immediate and the long-range effects of the cleaning are known. The gentlest method possible should be selected to achieve an appropriate level of cleanliness. |
Cleaning masonry surfaces with more aggressive methods, without testing or without sufficient time for the results and accompanying effects of the testing to be evaluated. |
| Protect adjacent materials during cleaning to avoid damage by abrasion or water infiltration. |
Cleaning masonry without protecting surrounding materials. |
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Other Surface Treatments
| Recommended
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Not Recommended
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| Remove damaged or deteriorated paint or other coatings only to the next sound layer using the gentlest method possible, such as hand scraping, prior to recoating.
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Removing paint or other coatings that are firmly adhering to, and thus protecting, masonry surfaces.
Using methods of removing coatings that are destructive to masonry, such as sandblasting, application of caustic solutions or high-pressure water-blasting.
Using tools that could damage the masonry, such as rotary grinders or sanders. |
| Apply compatible paint or stucco following proper surface preparation.
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Failing to follow manufacturers' product and application instructions when repainting masonry.
Applying paint or stucco to masonry that has been historically unpainted or uncoated.
Removing paint from historically painted masonry, unless it is causing damage to the underlying masonry.
Removing stucco from masonry that was historically never exposed, or radically changing the type of paint or coating or its colour. |
| Repaint or re-stucco with colours that are historically appropriate. |
Using new paint or stucco colours that are inappropriate to the Cenotaph/Monument. |
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Repairing Masonry Elements
| Recommended
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Not Recommended
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Repair deteriorated masonry elements by the most appropriate minimum intervention method available, including:
- re-pointing;
- re-setting loose masonry units;
- pin and glue repairs;
- dutchman repairs;
- stone consolidation;
- local replacement of masonry units; or
- dismantling and rebuilding.
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Replacing masonry that can be repaired.
Removing deteriorated masonry elements that could be stabilized, repaired and conserved. |
| Create a mock-up of each type of masonry repair involved in the conservation project as part of the repair contract in order to refine repair techniques, mortar mixes, replacement materials, and establish the acceptable quality of workmanship for each repair type. It is important to prepare the mock-ups far enough in advance of the repair work to allow them to fully cure before they are evaluated. |
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Re-pointing
| Recommended
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Not Recommended
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| Re-point mortar joints where there is evidence of deterioration such as disintegrating mortar, cracks in mortar joints, or loose masonry units.
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Removing non-deteriorated or acceptable mortar
from sound joints, then re-pointing the entire
Cenotaph/Monument to achieve a uniform
appearance.
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| Create new weep or drainage holes at the base of a masonry assembly to assist in the drainage and drying out of the masonry assembly when moisture infiltration into the assembly is an ongoing problem. |
Damaging the stone or brick units to create the drainage holes by drilling holes that are wider than the mortar joints. |
| Remove deteriorated mortar by carefully raking the joints using properly sized hand tools to avoid damaging the masonry. |
Using rotary grinders or electric saws to remove mortar from joints.
Failing to remove deteriorated mortar prior to repointing or not removing enough mortar to produce a proper depth of new mortar. The depth of new mortar pointing should equal at least twice the width of the mortar joint being re-pointed. |
| Match the aesthetic properties of the re-pointing mortars with the original mortar, including: colour, texture, aggregate, width, and, joint profile. |
Using a "scrub" coating technique to repoint instead of traditional repointing methods.
Re-pointing mortar joints with a synthetic caulking compound. |
| Use mortars that will ensure the long-term preservation of the masonry assembly. Mortar should be compatible with the properties of existing masonry units, including: strength, porosity, absorption, and vapor permeability. |
Re-pointing with mortar too high in Portland cement which can create bonds stronger than the masonry units and can cause damage as a result of the differing coefficients of expansion and the differing porosity of the materials. |
| Carry out a comparison of the existing and proposed mortar mixes to determine their mechanical and aesthetic properties for comparison. Carry out the comparison far enough in advance of the repair work to allow sufficient time to identify and source appropriate replacement materials. |
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| Replace failed or deteriorated joint sealants including caulk, putty and lead, in kind, unless the type of material used is adversely affecting the surrounding materials of the Cenotaph/Monument. Replacement sealants should match the original in colour, texture, and finish. |
Failing to follow manufacturers' product and application instructions when applying sealants or caulks.
Using sealants which can discolour as a result of absorbing soil or dirt particles from atmospheric pollutants.
Using sealants or caulk in joints that were originally pointed with mortar. |
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Re-setting Loose Masonry Units
| Recommended
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Not Recommended
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| Reset loose or displaced masonry units by removing all deteriorated mortar around the masonry unit, and resetting the unit fully bedded in new mortar. |
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Pin and Glue Repairs
| Recommended
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Not Recommended
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| Re-attach fragments of stone that have broken off by pinning and gluing where the fractured piece of stone is intact and to be retained. Use adhesives that are compatible with the stones' coefficient of thermal expansion to bond the fragment back onto the stone. Bonding larger fragments may require the addition of reinforcement using non-corroding materials for the pins, such as stainless steel, to mechanically attach the fragment to the stone. Important properties of the adhesive should include the ability to: harden without shrinkage; bond well with the stone; not adversely react chemically with the stone; be reversible or removable; remain stable with age, not becoming brittle with exposure to ultraviolet radiation, for example; and not be wicked out by moisture. Keep the adhesive 6mm [1/4 inch] to 12mm [1/2 inch] back from the visible faces of the stone so that the remaining crack can be filled with a cementitous material. |
Replacing a stone, when a re-attaching a broken off fragment is possible.
Using hard or rigid adhesives on materials with significant coefficients of expansion such as slate or sandstone.
Permitting the adhesive to drip, be smeared or otherwise exposed on the stone surface as they can change the colour of the stone, and can react with ultraviolet radiation, becoming brittle and very dark in color. |
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Dutchman Repairs
| Recommended
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Not Recommended
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Repair chipped or locally deteriorated parts of larger stone units with dutchman repairs when the fractured piece of stone is lost. Dutchman repairs involve carefully fitting a new piece of stone into a pocket cut into the existing stone and finishing the new piece to match the surrounding existing stone.
When using a dutchman repair, carefully match the physical, mechanical, and aesthetic properties of the replacement stone to the existing stone. Use non-corroding materials for pins, such as stainless steel to improve the degree of attachment between the repair stone and the original stone.
Use adhesives that are compatible with the stones' coefficient of thermal expansion to bond the repair stone to the original stone. Refer to the guidelines for pinning and gluing stone fragments, for other recommended properties of the adhesive. Keep the adhesive 6mm [1/4"] to 12mm [1/2"] back from the visible faces of the stone so that the joint between the repair stone and original stone can be filled with a cementitous material. Match the colour of the cementitous material used to fill the joint between the repair and original stone to the colour of the stone.
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Replacing a stone, when a partial repair using a dutchman is possible. |
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Stone Consolidation
| Recommended
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Not Recommended
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| Use synthetic consolidants to return structural integrity to a carving or statue where the naturally occurring binders and cements have been lost and the stone is beginning to disintegrate. |
Using untrained personnel to return structural integrity to a carving or statue, thus causing further damage to fragile historic materials. |
Determine if consolidating is the most appropriate method of treatment by evaluating this method against other methods of conservation, such as dutchman repair, plastic mortar repair or replacement.
Consolidants should be able to deeply penetrate the stone, harden without shrinkage, and bond well with the stone. In addition they should not adversely react chemically with the stone, be reversible or removable, remain stable with age, neither changing colour nor becoming brittle with exposure to ultraviolet radiation. They should not be wicked out by moisture, not migrate to the surface of the stone over time; and, not alter the surface appearance of the stone. |
Using untested consolidants, thus causing further damage to fragile historic materials. |
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Local Replacement of Masonry Units
| Recommended
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Not Recommended
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| Replace extensively deteriorated or missing parts of masonry elements, in kind with new stone or brick. The new work should match the old in form and detailing. |
Replacing an entire masonry element, such as a column, when limited replacement of deteriorated and missing components is appropriate.
Using replacement material that does not match the existing masonry element.
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Match the physical and mechanical properties of new stone used in repairs and replacements as closely as possible with the existing stone:
- stone type;
- compressive strength (ASTM C170-90, wet and dry);
- modulus of rupture (ASTM C99-87, wet and dry);
- absorption (ASTM C97-02);
- bulk specific gravity (ASTM C97-02).
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| Match the aesthetic properties of the new stone, used in repairs and replacements, with the existing stone, including color, texture, density of grain or bedding planes, number and size of inclusions, and finish. |
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Match the physical and mechanical properties of the new brick, used in replacements, as closely as possible with the existing brick, including:
- brick material type;
- compressive strength;
- modulus of rupture;
- absorption;
- bulk specific gravity.
Reference ASTM standard C67-03 for testing procedures.
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| Match the aesthetic properties of the new brick, used in replacements, with the existing brick, including size, colour, and texture. |
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| Carry out testing and comparison of the existing and replacement stones or bricks to determine their physical, mechanical, and aesthetic properties for comparison. Carry out testing far enough in advance of the repair work to allow sufficient time to identify and source appropriate new materials. Carry out comparisons under both wet and dry conditions and under natural light at the Cenotaph/Monument. |
Tasking the Contractor with the responsibility of sourcing the replacement material. |
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Dismantling and Rebuilding
| Recommended
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Not Recommended
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| Dismantle and rebuild the entire Cenotaph/Monument or large parts of it, when the integrity of the assembly of the masonry, or its supporting foundation, is badly deteriorated, putting the security of the Cenotaph/Monument at risk. Decide if dismantling and rebuilding is appropriate by evaluating it against other less intrusive methods. |
Dismantling a masonry assembly that can be repaired by other less intrusive means. |
| When dismantling, number and record each stone prior to removal to ensure accurate reconstruction in the original order and stone location. Record the thickness of typical joints at critical locations in the assembly to permit an accurate reconstruction. When rebuilding, replace ferrous dowels or cramps with new dowels or cramps fabricated from non-corroding material such as stainless steel. |
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