A brick repointing job looks simple, but it’s actually not easy, and isn’t something the average homeowner should take on, since you can end up damaging a wall and creating a big mess. There are 4 steps involved; preparing the joint, mixing the mortar, filling the joint with the mortar, and finishing and shaping the joint.
Preparation for repointing is the step during which an inexperienced workman most risks doing permanent damage, and merely brushing out loose mortar and refilling will produce a joint which, although it may look fine, will decay and loosen within months.
All the crumbling, loose, powdery, cracked or overly soft mortar should be raked out to a consistent depth the full width of the joint. The optimal depth to cut out to make sure of getting good adhesion is between 2 and 2 ½ times the width of a vertical joint, which in the case of brickwork, is ½ inch to ¾ inches deep. This will guarantee enough contacting surface, friction and surface adhesion between bricks and mortar to get a good bond, even without using specialized mortar bonding agents.
If there is deteriorated or loose mortar beyond the ½ inch to ¾ inches depth, this should also be cleaned out. The mortar needs to be cleanly removed, leaving square corners and flat surfaces at the back of the raked out area.
Power tools should almost never be used for cleaning out joints, only hand tools. The best tool is a small head chisel; the chisel head should be no wider than half the width of the mortar joint.
Even though manually removing old mortar is hard, time consuming labor, you run far less of a risk of damaging your masonry as opposed to using a power tool. Impact hammers or circular saws with carbide blades can damage the brick’s edges and leads to accelerated weathering and moisture incursion.
Any loose bricks will need to be reset, and any bricks with pieces which have broken off, should be replaced before mortaring begins. If you are having particular trouble finding bricks matching the original ones, then ceramic glue can be used to reattach loose pieces of brick to the original.
With newer brickwork and masonry, an off the shelf mortar mix can usually be used, but for older buildings, it becomes necessary to custom mix to match the hardness of the mortar to the old mortar’s hardness. See our page on choosing a mortar. You can check the match of the old and new mortars by taking a sample of raked out old mortar, break it in two so as to expose the interior and then compare it side by side to several test samples of different new mortar mixes that have been properly cured.
A plastic bucket or wheelbarrow makes a good container for mixing your mortar. So as to prevent lumps and uneven texture, color and strength, mix the mortar slowly by adding half the recommended amount of water, mixing for around five minutes, then adding the remaining water mount in smaller portions until the correct consistency is reached. When is that? When the mortar sticks to a trowel held upside down without dripping excess water.
Don’t mix up too big a batch, as it will only be workable for one or two hours before hardening begins.
Filling the Joint with Mortar
Before filling the joint, it should be dampened by spraying some water on the brick surface; the surface should be moist but not wet, with no freestanding water. This inhibits absorption of water into the brick before it has a chance to set and gives better adhesion and strength to the mortar.
Fill the joint, using a brick trowel, in a series of layers, letting the layer harden before applying the next one. Applying mortar in this way lessens the overall shrinkage, prevents air pockets and gaps and improves watertightness. Joint areas deeper than 1 inch are to be filled first by packing mortar in multiple layers until the joint back surface is flat.
Next, apply a 1/3 inch thick mortar layer several feet in length to the back of the joint, and allow it to harden. Continue compacting layers of 1/3 inch until the joint is filled flush to the brick’s exterior surface. For filling narrow joints cleanly, it is best to protect masonry by masking off adjoining bricks with lengths of masking tape, or alternately, applying the mortar between 2 strips of wax paper placed in the joint.
Finishing and Shaping Repointing
Mortar must be finished, or “tooled”, to give it a denser, smooth outer layer which will not be too porous. Even though some brick joints in the masonry you are repointing may have been left untooled, it is good practice to tool and then to allow the joint to weather until it matches.
Tooling is done by smoothing the mortar joint with a finishing tool called a slicker; it should be narrow enough to be placed inside the joint. Pull the slicker firmly across the mortar surface to compress the wet mortar. Compressing brings the mortar’s binding agent to the joint surface and produces a slick film. The film will naturally weather away, typically within one year.
It is critical to perform the tooling at the right time, which is when the mortar is almost but not quite dry. Mortar tooled when too soft will have a color lighter than it should be, may not match existing mortar, and can develop hairline cracks. Tooling mortar when too hard can cause unsightly dark streaking called tool burns, and cause bad closure of the mortar against the brick. This is one example of the specialized experience required for repointing.
Joints can be finished with number of different shapes to their cross section profile. The joint shape plays an important role in the durability, aesthetics and weathering of the brickwork. Care should be taken to match the original joint shape profile as close as possible.
Mortar joints should shed off rainwater and moisture in order to prevent moisture accumulation and ingess. To this end, the joint profile should be concave in shape, rather than projecting from the brick surface, which would trap water on every course of bricks.
Joint shape is formed by the shape of the finishing slicker tool used. They are available in several styles. A rounded concave joint is formed by the convex shaped slicker, sharp V-joints are formed by V-joint slickers and son on. There is a decorative joint called the Grapevine joint, which is flat with a deep u-shaped shadow line in the center, made by a grapevine slicker with a central rib.
Incidentally, the term tuckpointing is sometimes used as referring to repointing in general; however, it was originally a special type of decorative joint used in rough stonework with wide, irregular joints. In order to give the appearance of more regular and narrow joints, associated with more costly masonry, joints were first filled with mortar colored to match the stonework. A narrow groove the width of a normal joint was then made in the mortar and filled in (“tucked”) with a white lime powder strip to mimic common mortar.
There is not much in the way of cleanup to be done if the repointing has been properly performed. Any stray bits of mortar can be removed from brick with dry, stiff brush before the mortar fully hardens (1 to 2 hours), but after it has initially set. If the mortar has hardened, it must be cleaned away from the brick with a chisel or wooden paddle. Mortar smears on the brick surface need to be cleaned off after 1 or 2 days has passed in order to give the mortar some resistance, using plain water and a natural bristle, stiff brush.
With harder mortars containing lower amounts of lime, a “bloom” known as efflorescence will sometimes appear on repointed brick after a few weeks. It will, however, disappear in the course of normal weathering and is nothing to be concerned about. Of course, the new mortar will appear lighter in color to the existing mortar, no matter how careful you were in matching colors and texture, and this also will eventually become less and less apparent with aging. Your repointed brick masonry should last for many decades; a year or two of miscolored mortar is a small price to pay.
Brick Photo by Jeremy Schultz, Creative Commons Attribution License, Mortar Bucket Photo by Jennifer Dickert, Creative Commons Attribution License, Finished Joint Photo by Lauren, Creative Commons Attribution License