Repoint Crumbling Mortar Joints Before Water Gets Behind Them
Sandy, recessed joints are the wall asking for help. A bag of the right mortar and a patient weekend buys another forty years.
Mortar is designed to be the sacrificial part of a brick wall. It is softer than the brick, it takes the weather, and after 50 to 100 years it turns sandy and falls out of the joints. Repointing — raking out failed mortar and packing in new — is slow, repetitive, and entirely within reach of a patient homeowner. What ruins it is hurry: shallow raking, the wrong mortar, and joints struck before they are ready.
Why the mortar has to be softer than the brick
Old brick, especially anything laid before about 1930, is soft. Fill its joints with modern high-strength mortar and the brick becomes the weakest part of the wall; freeze-thaw cycles then spall the brick faces instead of the joints. For historic brick use Type O or a lime-based mortar. For brick from the 1950s onward, Type N is the standard. Type S belongs below grade in block walls, not in your chimney. Buy premixed mortar and buy pigment separately if the existing joints are anything other than gray.
Rake out to a proper depth
Remove old mortar to at least 3/4 inch deep, or two and a half times the joint width, whichever is greater. Shallow repointing peels off in a few winters. Use a hand raker for soft mortar and a cold chisel with a 3-pound hammer for stubborn spots. Only bring in an angle grinder with a tuckpointing blade if you have practice — it cuts brick as happily as mortar. Rake to a square back, not a V, so the new mortar gets full depth. Do the head joints (vertical) and bed joints (horizontal) both.
Clean and dampen
Brush every joint with a stiff brush, then blow or vacuum the dust out. Dry brick sucks the water out of fresh mortar and the joint fails from the inside. Mist the wall with a hose until the brick is damp but not dripping about 30 minutes before pointing, and again right before you start on a warm day.
Mix a batch you can use in 90 minutes
Mix to a consistency that holds its shape on a trowel — drier than you expect, like damp sand that clumps. Small batches only, and never add water once it starts to stiffen. Test your color on a scrap board and let it dry two days; wet mortar reads two shades darker than cured mortar, and the match you approve on the hawk will be wrong on the wall.
Pack the joints in layers
Load the hawk, hold it level with the joint, and push mortar in with the tuckpointing tool in 1/4-inch layers, compacting each layer before adding the next. Bed joints first, then head joints. Fill flush or slightly proud of the brick face. Work top to bottom so you clean drips as you go instead of smearing them into finished work.
Strike when thumbprint-hard
Wait until the mortar takes a thumbprint without sticking — 30 minutes to 2 hours depending on weather. Then strike to match the existing profile: concave with a jointer, weathered or flush with the trowel edge, raked with a raker set to depth. Brush lightly with a soft brush afterward to knock off crumbs. Too early and the joint smears across the brick; too late and it won’t tool at all.
Never repoint in freezing weather or in direct hot sun. Below 40 degrees the mortar won’t cure; above 90 in full sun it dries before it hydrates and turns to powder within a year. Work the shady side of the day or hang plastic for shade, and keep the joints damp for three days.
Mortar is supposed to fail so the brick doesn’t. Give it the depth and the softness to keep doing that job.
Cure and keep watching
Mist the new joints lightly for three days if the weather is dry. Wait at least a month before any cleaning, and keep acid washes away from fresh mortar entirely. Once a year, walk the wall in low sun, which throws recessed joints into shadow, and rake and repoint any that have opened. A wall repointed this way should go another 40 years before it needs you again.
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