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Reviewed by Tom Reilly — Senior Editorial Reviewer — Roofing, Carpentry & General Contracting

Fix it yourself · Concrete Mason

Chimney mortar crumbling or deteriorating: fix it yourself, or call a concrete mason

The mortar joints between chimney bricks endure the worst conditions in your home — direct sun, driving rain, freeze-thaw cycles, and constant exposure to combustion gases from the inside. Over 20–40 years the mortar erodes, cracks, and eventually crumbles away, leaving gaps between bricks. This process (called spalling or joint deterioration) lets water penetrate the chimney structure, which accelerates the damage: water freezes inside the gaps, expanding them further, and can travel down into the flashing, attic, or even interior walls. Left unrepaired, a deteriorating chimney becomes a structural risk — loose bricks can fall, and water infiltration causes mold and rot. The fix is called tuckpointing (or repointing): a mason grinds out the old mortar to a uniform depth and packs fresh mortar into the joints. Cost is typically $500–$2,500 for a standard residential chimney, depending on height, access, and how many joints need work. A chimney cap ($200–$600 installed) prevents most direct rain and animal entry.

Is this your problem?

Symptoms to look for

  1. 01

    White, sandy, or powdery residue (efflorescence) on chimney bricks

  2. 02

    Visible gaps, cracks, or missing chunks of mortar between bricks

  3. 03

    Pieces of mortar or brick found on the roof or ground near the chimney base

  4. 04

    Water stains on the ceiling or walls near the chimney after rain

  5. 05

    Bricks that feel loose or shift when pressed

Fix it yourself

How to fix chimney mortar crumbling or deteriorating

Chimney mortar crumbling or deteriorating

hard 3–8 h

Tools: binoculars, ladder with a stand-off, raking tool or a grinder with a mortar blade, tuck pointer and hawk, stiff brush, spray bottle, safety glasses and dust mask · Materials: type N mortar (or a lime mortar for pre-1930 brick), chimney crown sealant, masonry water repellent (breathable siloxane)

Steps

  1. Inspect from the ground with binoculars first, then from a ladder set beside the chimney — not on the roof — and note whether the damage is a few joints or every joint.
  2. Only repoint what you can reach from the ladder or a flat, low roof; anything above the first storey is staging work.
  3. Rake the failed joints out to 2 cm (¾ inch) deep, brush the dust out, and mist the joints with water so the brick does not suck the moisture out of the new mortar.
  4. Mix a small batch of type N mortar to a stiff, workable consistency and pack it in layers with a tuck pointer, pressing hard; strike the joint to match the originals once it is thumbprint-hard.
  5. Keep the joints damp for two days by misting, and do not work in frost or in direct summer sun.
  6. Seal a cracked crown with crown sealant and brush a breathable water repellent over the whole chimney in dry weather — most mortar loss starts with water from above.

Stop and call a pro if

  • the chimney is above one storey and cannot be reached from a ladder — that is scaffold or roof work
  • bricks are loose, cracked or the chimney leans
  • mortar is missing to more than 2.5 cm (1 inch) deep over a large area, or the crown is broken through
  • there is a water stain inside near the chimney — the flashing or liner may be the real leak

Rules in the US: Pre-1930 brick needs a soft lime mortar; hard portland mortar cracks the old brick within a few winters.

Rules in the Netherlands: Bij een monument of beschermd stadsgezicht kan voegwerk vergunningplichtig zijn — check bij de gemeente vóór je begint.

What a pro does that you can't

A mason repoints the full chimney from staging, rebuilds the crown, replaces spalled bricks and checks the flashing and liner, which are usually failing at the same age.

DIY cost: $30–80 in mortar, sealant and repellent

Get a free quote

Who to call

Concrete Mason

A mason repoints the full chimney from staging, rebuilds the crown, replaces spalled bricks and checks the flashing and liner, which are usually failing at the same age.

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FAQ

Frequently asked questions

Who should I call for: Chimney mortar crumbling or deteriorating?

Call a licensed concrete mason. Concrete Masons have the specialized training, tools, and insurance to diagnose chimney mortar crumbling or deteriorating safely and stand behind the fix. Most offer free quotes and can visit the same day or the next.

Can I fix this myself?

Often, yes: the guide above has 6 steps (hard, 3–8 h, $30–80 in mortar, sealant and repellent). Stop and call a concrete mason if the chimney is above one storey and cannot be reached from a ladder — that is scaffold or roof work.

How fast can a pro come out?

Most concrete masons offer same-day or next-day visits for non-emergency issues. True emergencies (burst pipes, gas smell, no heat in winter) are typically handled within 1–4 hours.

How much does it cost to fix?

Costs vary by severity and your location. Submit a free quote request to get real pricing from local pros in your area.

What are the signs of: Chimney mortar crumbling or deteriorating?

White, sandy, or powdery residue (efflorescence) on chimney bricks. Visible gaps, cracks, or missing chunks of mortar between bricks. Pieces of mortar or brick found on the roof or ground near the chimney base. Water stains on the ceiling or walls near the chimney after rain. Bricks that feel loose or shift when pressed.

Who to call

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