How to Patch Brick Around a New Penetration
Why this matters
A new line through a brick wall leaves two repairs, the hole and the mortar the drilling loosened around it. Most trades fill both with whatever bag of mortar mix is on the truck, and on a modern brick wall that mostly works. On an old house it does lasting damage. The bagged mix is harder and less permeable than the soft mortar and brick around it, so water and freeze-thaw stress concentrate in the brick instead of the joint, and the faces of the bricks around the patch spall off over a few winters. The mortar you match the old joint with is a decision you make with test batches, a week before the final pointing, and it gets written down. The reasoning is owned by Why Hard Mortar Ruins Soft Old Brick; this card is the procedure.
Before you drill: what kind of wall
Solid masonry or veneer. A house built of solid brick, common before about the 1940s, has two or more layers of brick bonded together, often with a row of bricks laid end-out (headers) every few courses, and plaster on the inside. A brick veneer is a single layer of brick over an air space in front of a framed wall with sheathing and a water-resistive barrier. In a veneer the line crosses that cavity and has to be sealed at the barrier as in How to Flash an Exterior Wall Penetration Into the WRB. In a solid wall there is no cavity and the masonry itself is the water defense, which makes the mortar the whole repair.
Silica, at every tool that cuts this wall. Brick and mortar contain crystalline silica. On construction work 29 CFR 1926.1153 governs it, and its Table 1 sets the controls by tool. Table 1 lists a rig-mounted core drill with integrated water delivery, and a handheld drill with a shroud and dust collection system; a handheld core drill run wet is common and keeps dust down, but it is not a Table 1 entry, so that method falls under the standard's exposure-assessment route instead. A handheld grinder used to remove mortar is the Table 1 tuckpointing entry: a shroud and dust collector, plus a respirator, assigned protection factor 10 for four hours or less a shift and 25 for more than four, worn under a written 29 CFR 1910.134 program. Check the current text of Table 1 for the full conditions. On soft lime mortar, hand raking with a plugging chisel is usually fast enough, makes far less dust, and does not cut the brick edges, which a grinder on old brick nearly always does.
Wet mortar is caustic. Lime and portland cement mortar burn skin and eyes. Gloves and eye protection whenever you mix or point; wash mortar off skin promptly; for a splash in the eye, flush with clean water for 15 minutes and get medical attention.
The steps
1. Put the hole on a joint where the hole is small enough. A cable, a small tube or a conduit up to roughly the joint's width plus a little goes through a mortar joint, and the patch is mortar only. Anything wider than the joint has to cut into brick, so center it where it breaks the fewest brick faces, usually on a bed joint at mid-length of a brick rather than at a corner where four bricks meet. Reason: mortar is the sacrificial, repairable part of the wall; brick is not. If you skip it: the bit wanders onto a brick edge, spalls its face, and that brick is a replacement in a size and color you may not find.
2. Core, do not hammer. Use a diamond core bit, wet, at the size the sleeve needs plus room for packing, without hammer action. Reason: a rotary hammer shocks the bricks around the hole loose from their mortar. Hazard: water and a corded drill together: use a drill rated for wet coring or a cordless one, plug into a GFCI-protected outlet, and keep the cord out of the water running down the wall.
3. Set the sleeve. A PVC or metal sleeve, sized for the line with room to move, set sloping slightly down toward the outside so water in it drains out, and cut flush with the face of the brick or a hair proud. Reason: the line moves with temperature and must not bear on the patch.
4. Rake out the loosened joints to sound mortar. Find the extent of the damage by tapping and scraping around the hole: loosened mortar crumbles under a screwdriver tip and sounds dull. Rake those joints back with a plugging chisel to a depth of 2 to 2 1/2 times the joint's width, the depth the National Park Service's Preservation Brief 2 gives for repointing, and until you reach sound mortar. Square the back of the raked joint and do not undercut the brick. Reason: new mortar needs a deep, square key; a shallow patch over loose mortar pops out the first winter. Hazard: rake with eye protection, the chips fly at face height.
5. Make and test sample batches a week ahead. Match three things to the old joint: hardness, color and texture. Hardness first: the new mortar must be no harder than the old and no harder than the brick. Mix two or three small batches from a measured proportion of portland cement, hydrated lime and sand, by volume, record each on the card shown in the worked example, press each into a joint between two scrap bricks, and let them cure for about a week before judging. Reason: mortar dries much lighter than it looks wet, and its final hardness only shows once it has cured. If you skip it: you point with a mix that looks right wet and dries gray and hard.
6. Point in lifts. Dampen the raked joints so dry brick does not suck the water out of the new mortar, with no standing water. Pack the mortar into the deepest areas first, in layers about 1/4 in thick, and let each layer reach thumbprint-hard, where a pressed thumb leaves a print but no mortar sticks to it, before the next. Reason: a deep joint filled in one push shrinks and pulls away from the back. Fill the gap around the sleeve the same way.
7. Tool the joint to the old profile. When the last layer is thumbprint-hard, tool it to match the old joints: concave, flush, struck, raked, whatever the wall shows, with a jointer that matches the old width. Brush off crumbs when they are dry enough not to smear. Reason: a joint tooled to a different profile reads as a patch even in the right color, because the shadow line changes.
8. Keep it damp while it cures. Mist the patch several times a day for the first three days, shade it from direct sun and wind, and keep rain and frost off it. Do not point when the temperature is expected to fall to freezing before the mortar has cured; a common mason's floor is 40 F and rising. Reason: lime-rich mortar gains strength slowly and needs moisture to do it; dried too fast it is weak and powdery at the surface. Seal the line inside the sleeve with a sealant suited to the line and the masonry.
Worked example: a conduit sleeve through a 1920s wall
An electrician runs a cable to a detached garage through the solid brick wall of a 1926 house. The sleeve is 1 in PVC, cored at 1 1/4 in. The old joints are 3/8 in wide, tooled concave, buff with small white lime lumps, and soft enough to scratch with a key. The brick is a soft, sandy-faced red.
Placement. At 1 1/4 in the core is bigger than the 3/8 in joint, so it cannot sit in the joint alone. The electrician centers it on a bed joint halfway along a brick, so it bites into one brick above and one below the joint, about 7/16 in into each: 1 1/4 in minus the 3/8 in joint is 7/8 in, shared between two bricks. Cored wet, no hammer.
Raking. Tapping found loose mortar along about 10 in of the cored bed joint and in the two head joints nearest the hole. Raked by hand to a depth of 2 times the 3/8 in width, which is 3/4 in, where the mortar was sound. 2 1/2 times would have been 15/16 in; 3/4 in was the depth at which the scraping stopped finding loose material, which is within the range.
The card. Batches were mixed on the first visit, a week before the pointing visit:
MORTAR SAMPLE CARD - 1926 house, north wall
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Old joint: 3/8 in, concave, buff, white lime
lumps, scratches with a key
Sand A: masonry sand, light tan, fine
Sand B: coarser sand, darker tan
Measured by volume, level scoop, damp sand
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Batch P : L : S Type Sand Day 7
1 1 : 1 : 6 N all A too gray;
key will not
scratch: OUT
2 1 : 2 : 9 O all A scratches;
too light,
too smooth
3 1 : 2 : 9 O 6 A, 3 B scratches;
color and
grain match
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Swatch: in a joint between scrap bricks, held
beside a cleaned old joint, daylight
Chosen: batch 3. Misted daily, 7 days
P is portland cement, L hydrated lime, S sand. The types follow the proportion ranges in ASTM C270, the mortar specification, which applies where a contract or code invokes it: 1 : 1 : 6 falls in Type N, and 1 : 2 : 9 in Type O. Batch 1 was ruled out on hardness before color was even considered, because a mortar the key cannot scratch is harder than a joint the key can, and that is the failure this whole card is about. Batches 2 and 3 have the same binder and differ only in sand, and the change from all fine sand to a 2-to-1 blend with coarser sand fixed both the color and the grain. In batch 3, 6 parts A plus 3 parts B is the 9 parts of sand, two A to one B.
Pointing. On the second visit, joints dampened, batch 3 mixed from the card, packed in three lifts of about 1/4 in each to fill the 3/4 in depth, the gap around the sleeve packed the same way, tooled concave with a jointer matching the 3/8 in width. Misted three times a day for three days; the forecast low stayed above 45 F.
Result. A week later the patch scratches like the old joint, reads the same color from the street, and the two cored bricks show only the clean edge of the hole. The card goes into the job record with the sand sources named, so the next repair on this house starts from batch 3.
What changes the method
- A modern wall, built since the 1950s with hard brick and portland-rich mortar. The sample batches still match color, but a Type N mix is usually right in hardness, and the scratch test tells you so.
- A veneer. Point the brick the same way, and seal the line at the barrier behind the cavity as well.
- A cracked or spalled brick around the hole. Replacing a brick is its own repair, salvaged brick from a hidden part of the wall or a salvage yard, set with the same mortar.
References
- See related: Why Hard Mortar Ruins Soft Old Brick
- National Park Service, Preservation Brief 2, Repointing Mortar Joints in Historic Masonry Buildings
- ASTM C270, Standard Specification for Mortar for Unit Masonry, current edition
- OSHA 29 CFR 1926.1153, respirable crystalline silica in construction, Table 1; 29 CFR 1910.134, respiratory protection
- See related: How to Flash an Exterior Wall Penetration Into the WRB