How to Repoint a Chimney and Seal the Crown: Harness, Joints, Cap
Repointing the stack yourself: $585–$745 in mortar, sealer, a grinder and a harness, 8–14 hours on the roof.
- Walkable roof, dry, over 40°F, harness anchored to something structural. If any of those isn't true, this is a hire.
- Grind or chisel every failed joint out 3/4 inch deep, blow it clean, dampen the brick, and pack it with Type N mortar matched to the old — never Type S or a premixed 'concrete' patch on old brick.
- Seal a cracked crown with an elastomeric crown coat after filling the cracks; a crumbling crown gets recast, which is a mason's job.
- Bolt a stainless cap to the flue tile, water-repel the stack, and get a Level 2 inspection if the flue has never had one.
Before you start
Read the cost comparison first. The numbers favor DIY on the top of the stack — about $665 in mortar, sealer, a grinder, a cap and a harness against $1,100 from a mason to repoint, seal and cap — and barely on a cap and crown seal alone, where the harness is most of the $410 against $450. What decides it isn’t the money; it’s the roof.
This guide is for the masonry at the top of a chimney on a walkable, dry roof: repointing open joints, sealing an intact crown, fitting a cap. It isn’t for flashing, which is roofing and the usual leak; for a stack that leans, spalls or crumbles, which is a rebuild; for a steep or high roof; or for any chimney whose flue hasn’t been looked at with a camera. A Level 2 inspection first is the rule, because a cracked liner is the repair that no repointing fixes.
What you need
A roof harness with rope and a ridge anchor, an extension ladder with a stabilizer, an angle grinder with a tuckpointing blade and dust shroud (or a hammer and plugging chisel), a P100 respirator and safety glasses, a tuck pointer, pointing trowel, jointer and hawk, a caulk gun, wire brush and drill, Type N mortar with pigment, elastomeric crown sealer and crack filler, a stainless cap sized to the flue, and a gallon of siloxane water repellent. The priced list is on the cost page.
The three things that decide how it turns out
The anchor. A harness clipped to nothing is a costume. A ridge anchor screwed into rafters, or the rope around the chimney base on the far side, tied before your feet leave the ladder.
The mortar. Type N or softer, matched, packed 3/4 inch deep into clean, damp joints. Tuckpointing with the wrong mortar spalls the brick in a few winters; with a smear of caulk it lasts a season.
The crown. Sealed if it’s intact, recast by a mason if it isn’t. It’s the roof of the chimney, and everything below it fails when it does.
Step by step
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Inspect from the ground, then get the flue inspected
Binoculars: cap, crown, joints, spalling, lean, flashing. Look in the firebox for water stains and bits of tile. If the flue hasn't had a Level 2 camera inspection, book one before buying materials — a cracked liner changes the job.
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Pick the day and set up the roof
Dry, calm, 40°F and rising for 48 hours. Ladder tied off, a stabilizer at the eave, harness on with the rope to a ridge anchor or around the far side of the chimney base. Carry tools up in a bucket on a rope. Plastic on the shingles below the chimney to catch mortar.
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Grind or chisel the joints
Respirator and glasses on. Every failed joint out 3/4 inch deep to sound mortar, head joints and bed joints, without nicking the brick. Vacuum or blow the joints out; brush the faces. Check for loose or cracked brick as you go — a few can be reset in fresh mortar; many means a rebuild.
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Mix and match the mortar
Type N with pigment, mixed in small batches to a stiff, workable paste that holds its shape. Test the color on a scrap and let it dry — wet mortar is darker. Mist the joints with water.
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Pack, tool, brush
Tuck pointer and hawk: fill the head joints, then the bed joints, in compacted layers to flush. When thumbprint-hard, tool to match the old profile. When dry enough not to smear, brush the faces. Work the shady side first on a hot day.
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Seal the crown
Wire-brush and rinse it. Fill cracks over 1/8 inch and the joint around the flue tile. Bond-break tape around the tile, then two coats of elastomeric crown sealer to the edges and an inch up the tile.
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Fit the cap
Set the stainless cap over the tile, square, and drive the clamp screws snug. Check the screen is clear and the lid clears the tile by a few inches. Photograph the finished top for the house file.
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Cure, then water-repel
Keep the new joints damp for two days if it's hot; keep rain off for one. After a month, spray or roll a siloxane water repellent over the whole stack. Check the joints and crown from the ground each spring.
What would this cost you? The chimney repair calculator prices the DIY version with the tools you already own and a value on your time, next to a pro quote.
Frequently asked questions
How do I know if the roof is safe to work on?
Pitch under 6/12 (rises less than 6 inches per foot — you can walk it without holding on), dry, no frost, no moss, shingles that aren't brittle, and a chimney you can reach without standing on the ridge or the edge. A harness with a rope to a ridge anchor screwed into rafters, or around the chimney's base on the far side, and a ladder tied off at the top. A 8/12 or steeper roof, a wet day, a slate or tile roof, or a chimney at the eave of a two-story house is where the harness still isn't enough, and that's a hire.
What mortar do I use for chimney repointing?
Type N — medium strength, the standard for above-grade exterior brick — or a softer lime-rich mix for pre-1930 brick. Not Type S (too hard; it doesn't give with the brick, and the brick faces spall off instead), not premixed patching cement, not caulk. Match the color with mortar pigment against a dry sample of the old joint, and mix small batches to a consistency that holds a shape on the trowel. Firebrick and the smoke chamber need refractory mortar, which is a different job.
How deep do I grind the joints?
Three-quarters of an inch minimum, or two to two-and-a-half times the joint width, to sound mortar, on every joint that's cracked, crumbling or open — not just the worst ones. A grinder with a tuckpointing blade and a dust shroud does it fast and throws silica dust; a hammer and a plugging chisel are slow and clean. Don't widen the joints or nick the brick edges. Blow or brush every joint clean, then mist the brick so it doesn't suck the water out of the new mortar.
How do I pack the new mortar?
Load a hawk or a board, hold it against the wall under the joint, and push mortar in with a tuck pointer in layers — a quarter inch at a time, compacting each — the vertical (head) joints first, then the horizontal (bed) joints. Fill flush, let it firm up until a thumb leaves a print but no mortar sticks, then tool it to match the profile of the old joints (concave, flush, or weathered) with a jointer. Brush off the crumbs when it's hard enough not to smear. Keep it damp for a day or two if it's hot.
Can I seal the crown instead of replacing it?
If it's intact with hairline cracks, yes: clean it, fill cracks over 1/8 inch with a crown crack filler or a polyurethane sealant, and brush on two coats of an elastomeric crown sealer, out to the edges and up the flue tile an inch, with a bond-break tape around the tile so it can move. If the crown is crumbling, missing pieces, or was built as a thin mortar wash with no overhang, it needs to be broken out and recast in concrete with a drip edge — that's a form, rebar and a mason.
Which chimney cap do I need?
Stainless steel, sized to the outside of the flue tile, with a spark screen, bolted on with the screws it comes with — not galvanized, which rusts in a few years and streaks the brick. A multi-flue cap sits on the crown and covers all the tiles; a single-flue cap clamps to one. If there's no flue tile above the crown, a top-mount cap anchors into the crown. Measure the tile's outside dimensions and height above the crown before ordering.
Should I water-repel the brick afterward?
Yes, once the mortar has cured a month: a siloxane-based breathable masonry water repellent, sprayed or rolled on the whole stack, sheds rain while letting the brick dry out. Not a film-forming sealer, which traps moisture and spalls the brick. It's a gallon and an hour, and it's the difference between a repoint that lasts 25 years and one that opens up in 10.
Sources
- Brickmasons and Blockmasons (SOC 47-2021), Occupational Employment and Wage Statistics , U.S. Bureau of Labor Statistics, 2026-04
- How Much Does Chimney Repair Cost? , HomeGuide, 2026-09
- How Much Does It Cost to Repair or Replace a Chimney Crown? , HomeGuide, 2026-09
- How Much Does a Chimney Rebuild or Replacement Cost? , HomeGuide, 2026-09
- How Much Does Chimney Repair Cost? , Angi, 2026-09
- What Do Chimney Repairs Cost? , HomeAdvisor, 2026-09
- How Much Does Chimney Repair Cost? , This Old House, 2026-09
- Chimney Inspections: Levels 1, 2 and 3 , Chimney Safety Institute of America, 2026-09
- NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances , National Fire Protection Association, 2026-09
Figures last reviewed . See how we estimate.