What is Pointing?

By: Ivy Yuan 

The construction term pointing refers to the finishing of mortar joints in masonry, be it stone or brick. Mortar often does not have as long a lifespan as the brick it holds together, and over the years must be periodically removed and replaced. Repointing is the process of removing deteriorated mortar from the joints of a masonry wall and replacing it with new mortar. If properly performed, repointing restores the visual and physical integrity of the masonry, and therefore the longevity of the building envelope.

Mortar joints in exposed masonry are susceptible to weathering, which leads to water infiltration. This water infiltration, along with wind and pollution, causes the mortar to erode, and allows increase water infiltration. Mortar can also crack due to uneven settlement in a building’s foundation. As a structure settles into the ground over time, stress is transferred into the structure itself. This stress causes mortar joints to crack and peel, which again leads to further moisture entering the deteriorated mortar joints.

When the temperature falls below freezing, water in the masonry or the joints will freeze and expand. This phenomenon, commonly referred to as freeze/thaw cycles, will eventually cause the mortar and brick to spall. Cracking and deterioration can also occur if thermal expansion is not accounted for. This is more common in older buildings that were constructed without expansion joints. Contraction and expansion are very hard on mortar, particularly in areas that are subject to extreme temperature swings.

Telltale signs of mortar deterioration include mortar erosion exceeding ¼”, crumbling mortar, voids in the mortar, and hairline cracks in the mortar and bricks. These signs should not be ignored. To ensure there’s no further damage to the building, repointing should be performed as soon as possible.

The process of repointing starts with surface preparation. The existing masonry joints are cut out to a uniform depth of approximately ¾”, or until sound mortar is reached. The joints and surface are cleaned of debris, and thoroughly wetted. Once the surface is prepared, new mortar is carefully placed in the joints using a small trowel. the fresh mortar should be pressed firmly into the joints to form a strong bond with the existing interior mortar. The mortar joints should then be tooled to match the desired profile.

There are several different types of pointing profiles that can be achieved. Flush pointing is when mortar is pressed hard in the raked joints, and finished off flush with the edge of masonry units. The edges are then neatly trimmed with a trowel and straight edge. The flush joint helps bridge any height differences between adjacent bricks or stones, and prevents water and dirt from collecting in any low spots. Weathered pointing is a modification of flush pointing. The face of the pointing is kept inclined, with its upper edge pressed inside the face by about 10 mm. Weathered pointing throws off rain water and is considered fairly durable; however, it’s fairly difficult to achieve.

Concave pointing is formed by making the mortar flush with the face brick then struck with a brick jointer. The jointer keeps the mortar flush to the bed on the masonry units while slightly concaving the middle of the joint. Since it’s easy to achieve and offers a high level of weather protection, this joint is commonly used.

Beaded pointing is used almost exclusively in historical restorations. This joint looks like a raised bead on top of a flush joint. Beaded joints can be much more noticeable, making the mortar joints part of the structure’s visual aesthetic.

Recessed pointing, sometimes referred to as raked joints, is when the mortar joint is raked back a certain depth from the face of the brick. The mortar is first made flush with the brick and then raked out to the desired depth. Recessed mortar joints were mainly an aesthetic choice to draw attention to the brick rather than the mortar. There’s a lower resistance to weathering since the bed of the masonry below the joint is exposed. Water can sit on this bed joint and slowly be absorbed into the wall.

While mortar repointing is necessary, it’s erroneous to assume that repointing alone will solve all building envelope deficiencies. Water entry can result from deficiencies in flashing, waterproofing, gutters, lintels, sills, sealant joints, etc. It’s important to determine the root causes of any observed deterioration, and the sources of water infiltration, prior to performing any repair work. Without eliminating the source of the problem, mortar deterioration will continue, and repointing efforts will be a waste of time and money.

In most cases, the project costs associated with external restoration of a building are relatively low in relation to the benefits, particularly, the increase in property value and subsequent resale factor. Additionally, the reduction in risk, or potentially costly structural defects, outweigh any immediate costs.

 

 

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