Why Are In Stone Frequently Raked How Repair Mortar Joints

Lime mortars should be used for masonry repointing as they let the walls breathe. Detailed photographs should be taken before work begins of any sections to be dismantled and rebuilt. Mortar used in the original construction of traditionally built rubble masonry will deteriorate over time and repointing work will eventually be necessary. Masonry walls need to be maintained and repaired, just as roofs and rainwater goods do. The masonry has been re-pointed with a cement-based (or other inappropriate) mortar at an earlier date, which is causing problems to the building and/or the adjacent masonry and must be replaced with a more appropriate mortar.

This reduces the weather-proofing ability of the wall and encourages additional moisture to enter the masonry units and mortar joints. Repointing ashlar masonry, when required, is a vital part of building maintenance that helps to ensure the long life of the building. Care must be taken, and suitable tools used, to avoid damage when raking out ashlar masonry for repointing. By the mid-1800s, such façades were widely used on city tenements and villas and on rural farmhouses. Rough stone taken from the quarry was carefully cut into masonry blocks of precise dimensions and given tooled or smooth polished external faces. Rows of stones cut to exactly the same height, in random lengths, were laid with a ‘broken bond’. This gave the wall maximum load-bearing strength. The specifications for a project should describe in detail what is expected in each of these areas. The effects of ribbon style pointing over time. The effects of ribbon style pointing over time. Repointing is the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar. To ensure there’s no further damage to the building, repointing should be performed as soon as possible. The existing masonry joints are cut out to a uniform depth of approximately ¾”, or until sound mortar is reached. When selecting a joint type, it is important to consider both the desired architectural appearance and the weather resistance. Similar to the concave joint, tooling works the mortar tight and can help to prevent water penetration if done correctly. If not given the proper care, water can sit on top of the joint if it sticks out from the brick. This style has the effect of highlighting the stonework and making it stand out. For example, using a pointing device you could point at and select an icon from a list of icons.

Remove stone joints in Philadelphia home, Repointed in a take out joint/ recessed. Poured new concrete window wells.Recessed Mortar – Why Are Mortar Joints In Stone Masonry Frequently Raked

Any trapped moisture will expand if subjected to freezing conditions, and mortars may ultimately fail, often causing damage to the surrounding masonry in the process.

Blocked gutters or overflow pipes, for example, lead to damp masonry and can result in frost damage. Vapour permeability is essential for any mass-masonry walls to remain dry and functioning as intended. Buildings and their surrounding environment may change over time: for example a residential building may now be a roofless ruin. If possible, any inappropriate mortars which are causing accelerated decay of the adjacent masonry should be removed and replaced with more appropriate materials. Victorian squared rubble sandstone walling which has been repointed in a modern dense cement-based mortar, accelerating its decay, particularly at the stone/mortar interface.

Scotland in the construction of traditional ashlar buildings, but sandstone was used most often in most areas as it’s easy to cut. Lime mortar must be used and coarse sands that could clog the fine ashlar joints should be avoided. Scotland in the construction of traditional ashlar buildings, but sandstone was used most often in most areas. Despite being such a small part of the ashlar masonry façade, lime mortar joints give a building its ability to breathe. An ashlar wall constructed of squared stone blocks is inherently stronger than a rubble stone wall. Indent repairs to the sandstone may eventually be necessary where erosion is severe. Plant growth can also damage pointing, particularly where roots enter the wall. Lime based mortars should be used instead as these will allow the building to breathe and water vapour to escape. Ashlar masonry was built with great care and attention, and the precision required to repoint ashlar correctly demands considerable time and skill. Selection of contractors experienced in the restoration of older masonry is vital. Low-strength mortars are sensitive to extreme climate conditions during application and curing. It is important to ensure that repointing work does not cause undue disruption for building occupants or visitors. Mortar joints in exposed masonry are susceptible to weathering, which leads to water infiltration. This stress causes mortar joints to crack and peel, which again leads to further moisture entering the deteriorated mortar joints. Once the surface is prepared, new mortar is carefully placed in the joints using a small trowel. The mortar joints should then be tooled to match the desired profile. The edges are then neatly trimmed with a trowel and straight edge. Weathered pointing is a modification of flush pointing. This joint looks like a raised bead on top of a flush joint. Recessed mortar joints were mainly an aesthetic choice to draw attention to the brick rather than the mortar. Care must be taken to replace missing pinnings (small stones) that have fallen out from between large stones. How the lime mortar was applied is one such regional variation. Covering over pinnings will affect the appearance of a rubble masonry wall. The wall may collapse if the problem isn’t fixed. Take detailed photographs of the area to be repointed before work begins. If the space is any smaller there won’t be enough room for the new mortar to set and perform properly. Oscillating mechanical tools may also be used, but never rotary tools such as angle grinders. This can lead to premature deterioration and thus moisture intrusion. Saturated mortar joints can allow water to enter the cores and permeate throughout the wall. This is done on the top, and on the bottom of the joint. See more of the different types of joints which can be used here. The lifespan of the repointing work is thus much reduced when pinnings are missing. The mason may have to use the wooden shaft of a hammer to drive the pinnings into the spaces between the large stones. Repointing work should have a finish to match the wall’s original appearance. This reaction is part of the curing process. In its dry hydrate form, on the other hand, the lime is supplied in bags or sacks as a dry powder, and some premature carbonation is inevitable.

The correct choice of aggregates can be critical to the success of a lime mortar. Generally, the maximum aggregate particle size should be around one third of the joint width. However, achieving a visual match is also essential, particularly where old and new mortar are to co-exist, as in patch pointing. The choice of aggregate will also affect the mortar mix ratio, since particle shape and grading will change the void ratio. Any cementitious or other non-original and inappropriate mortars should be carefully removed, avoiding damage to adjacent masonry. However, care should be taken to ensure that sound, original lime mortars are left in place, in accordance with the principle of minimum intervention. Where masonry is relatively impervious and a suction bond may be difficult to achieve, joints may need to be raked out further, (say) at least twice the depth of the joint width, to provide a level of mechanical anchoring of the new mortar into the joint.

Hand tools such as plasterers’ small tools, half hacksaw blades and specially made steel hooks can be used to avoid damage to the stone arrises and widening of the joints.

Repointing Masonry — MADE

However, where historic masonry is concerned they should only be used by the most highly experienced craftsperson owing to the ease and speed with which they can damage masonry.

All loose and friable material must be removed prior to placing new mortar, as it requires a sound surface to adhere to. Preparation of the wall surfaces generally should include thorough cleaning down and removal of all loose material, dust, etc, and damping down before starting work.

Control of suction between the new mortar and the substrate is required. Impervious stones may require minimal or no damping down. For re-pointing, the mortar should be sticky but not wet. An appropriate pointing tool should be chosen to suit the width of the joint, thus preventing spreading of mortar or staining on the masonry faces.

The surface should then be lightly scraped back with the edge of the pointing tool or similar, to provide a rough, open-textured surface which is ideal for carbonation and curing, and for maximum evaporation of moisture from the joints once fully cured.

Overworking the surface of the mortar will result in surface laitance caused by lime particles being ‘worked’ to the surface, and forming an outer crust which may restrict carbonation of the mortar behind.

In drying conditions, new lime pointing will need to be dampened regularly (by lightly spraying) to prevent rapid drying. For hydraulic limes, retention of moisture within the mortar for the first few days is critical to ensure that the hydraulic set takes place because its hydraulic constituents react with water itself: thereafter, the remaining carbonation set requires cyclical light damping and slow drying.

The length of time required for the mortar to cure is also variable and will depend on environmental conditions, type of mortar used, its finish, and the mass of mortar in any one location.

Adequate protection can usually be achieved by close covering the new work with hessian and polythene sheeted panels placed against the face of the new work.

In conclusion, it is ultimately the role of specifiers and users of lime-based mortars to ensure that appropriate materials and methods are used for the finishing of historic masonry walling, whether lime pointing or otherwise.

General advice and guidance for lime pointing must be approached with caution. It is important that regional, local and building specific variations are considered to ensure that local and vernacular traditions affecting the character and appearance of our historic built environment are fully considered.

Specialist analysis of the existing mortar can help to ensure that its replacement looks right and performs equally well. An alternative to using tape is to sponge down the stone once the mortar has been applied but before it has dried fully. Ashlar walls were often built with slightly tapered blocks to help achieve very fine joints on the face. Excessive voids may result in mortar disappearing endlessly into the wall: these should be filled with a suitable grouting lime mortar. Once firmed up enough, the mortar surface can be finished by lightly scraping it with a small wooden spatula or similar tool. Protective tape should only be removed from the arrises (edges) of stones once the mortar is dry but not yet hard. Care should be taken to avoid spilling new mortar onto stone faces below the work area, as this can cause staining that is difficult to remove.

A flush finish is when the masonry joint is brought flush with the brick or masonry unit and is generally used if the masonry is to be painted to give walls a more uniform look.

The mortar between my bricks is soft, and seems to erode easily. There is mortar missing between some bricks in my wall. These joints most often occur above and below window or door openings, and at the base of masonry walls. To help obtain a consistent degree of dampness throughout the project, the sand can be protected from direct exposure to the elements (e.g., stored in a box or protected from sun and rain).

Mortar ingredients should be mixed into a homogeneous state. Small amounts of mortar can also be mixed using a hand drill with a whisk attachment used for plaster, or vigorously by hand, mixing no more than needed at one time.

A thorough blending of the ingredients is required. Plasticity improves with mixing time, although care must be taken if an air-entraining agent has been added, as too much mixing may introduce excessive air into the mix.

Sometimes the mortar is allowed to stand for a short while after mixing to allow good wetting of the ingredients. A brief remixing and addition of any extra water occurs after this period. Repointing should be done from the top of the façade down, in the shade, away from strong sunlight. The joint should first be wetted to minimize the loss of water from the fresh mortar into the masonry by capillary action. The extent of pre-wetting will depend on the water absorption capacity of the masonry and the temperature. For joints less than 25 mm deep, successive layers can be repointed without interruption. The next step is to rewet the joint and continue with the repointing. Thin joints may require protective tape to avoid staining of the units. Mixes containing hydraulic lime can be used over longer periods (up to 24 hours depending on hydraulicity), and lime-sand mortars can be kept indefinitely provided they remain damp.

Portland cement-lime mortar mixes should only be retempered once. If the masonry units have worn rounded edges, it is best to slightly recess the mortar away from the face. For historic masonry and for aesthetic effect, alternative finishes can be used and special tools may be needed. Mixes with slower-hardening hydraulic binders such as hydraulic lime should preferably be damp-cured for a minimum of seven days. However, excessive drying of the mortar (heating cold air has the effect of lowering its relative humidity) should be avoided; a high relative humidity level should be maintained within the heated enclosure.

Inspections after the joints have been raked out, cleaned and squared off, after any deep (25 mm) backpointing has been done and after the joints have been repointed will help ensure a high-quality job.

The repointing of older masonry buildings differs from new construction and extra care is required to ensure a successful project. Protection should be provided as necessary against freezing conditions.

Tooling Mortar Joints