Repointing the mortar around a brick fireplace hearth is well within reach for a capable DIYer. With the right materials, a bit of patience, and attention to safety, you can restore crumbling or cracked joints and keep your fireplace looking great for years to come. Here's how to do it properly in a New Zealand context.
Understanding the Job: What Is Repointing?
Repointing (sometimes called tuck-pointing) means removing deteriorated mortar from the joints between bricks and replacing it with fresh mortar. Around a fireplace hearth, mortar is exposed to repeated heating and cooling cycles, which causes it to crack and crumble over time. Left untreated, damaged mortar can allow moisture in, weaken the structure, and reduce the efficiency and safety of your fireplace.
Safety First
Before you start, keep these important points in mind:
- Check the fireplace is completely cold before working — ideally leave it unused for at least 24–48 hours.
- Mortar dust and old lime-based mortars can irritate lungs and skin. Wear a P2 dust mask, safety glasses, and gloves at all times when chiselling or mixing.
- If your home was built before the 1980s, old mortar may contain asbestos. Do not disturb it until you've had it tested by a qualified asbestos assessor. WorkSafe NZ has guidance on identifying and managing asbestos safely.
- If you notice structural cracking (wide cracks running through bricks, not just joints), or the firebox lining is damaged, stop and call a professional — this goes beyond cosmetic repointing.
Tools and Materials You'll Need
- Cold chisel and club hammer (or an angle grinder with a mortar raking disc for larger areas)
- Stiff wire brush
- Pointing trowel and margin trowel
- Bucket and mixing paddle (or a drill with a mixing attachment)
- Refractory mortar or fire-rated mortar mix — essential for the firebox and areas directly exposed to heat
- Standard bricklaying mortar (1 part cement : 1 part lime : 6 parts sand) for the outer hearth surround not exposed to direct flame
- Clean water
- Drop sheet to protect your floor
Choosing the Right Mortar
This is the most important material decision. The firebox (the inner chamber where the fire burns) and any joints directly exposed to heat must use a refractory (fire-rated) mortar, not standard cement mortar. Standard mortar will crack and fail quickly under high temperatures. Refractory mortar mixes are available at Bunnings and Mitre 10. Always follow the manufacturer's mixing and curing instructions.
For the outer hearth surround — the decorative brick area in front of and around the fireplace opening — standard bricklaying mortar is generally fine, as it isn't exposed to direct flame.
Step-by-Step: How to Repoint Fireplace Mortar
1. Rake Out the Old Mortar
Using a cold chisel and club hammer, carefully rake out the damaged mortar to a depth of at least 15–20 mm. This gives the new mortar enough depth to bond properly. Work methodically, joint by joint. Avoid hitting the bricks themselves — you want to remove mortar, not damage the brick faces.
2. Clean the Joints
Brush out all loose dust and debris with a stiff wire brush. Vacuum or blow out any remaining dust. Lightly dampen the joints with clean water — this prevents the dry brick from drawing moisture out of the new mortar too quickly, which weakens the bond.
3. Mix Your Mortar
Mix your chosen mortar to a firm, workable consistency — similar to peanut butter. It should hold its shape without slumping. Mix only as much as you can use in 30–45 minutes.
4. Apply the New Mortar
Using a pointing trowel, press mortar firmly into the joints, working from the back of the joint forward. Fill in layers if the joint is deep, allowing each layer to firm up slightly before adding the next. Avoid smearing mortar across the brick faces — keep it neat.
5. Finish the Joints
Once the mortar is thumb-print firm (not fully set), use the edge of your trowel or a jointing tool to finish the joints to match the existing profile — typically a flush or slightly raked finish on fireplace surrounds.
6. Clean Up and Cure
Wipe any mortar smears off brick faces with a damp sponge before they harden. Allow the mortar to cure slowly — keep the area out of direct draughts and avoid lighting the fire for at least 48–72 hours (or as directed by the mortar manufacturer). For refractory mortar, a gradual curing fire (small, low fires over the first few uses) helps the mortar harden fully.
Matching the Mortar Colour
Mortar colour can vary significantly depending on the sand and cement used. If appearance matters, buy a small amount of mortar first and let a test patch dry fully before committing — mortar lightens considerably as it dries. PlaceMakers can sometimes help with colour-matching advice.
Does This Work Require a Building Consent?
Cosmetic repointing of an existing fireplace hearth is generally considered maintenance and does not require a building consent under Schedule 1 of the Building Act. However, if you are making structural changes or rebuilding a significant portion of the fireplace, consent may be required. Always confirm with your local council if you're unsure. MBIE Building Performance has useful guidance on what work requires consent.
When to Call a Professional
Call a qualified bricklayer or mason if:
- Cracks run through the bricks themselves, not just the mortar joints
- The firebox lining (refractory bricks) is damaged or spalling
- You suspect asbestos in old mortar
- The damage is extensive or the chimney structure appears compromised
- You're unsure whether your fireplace meets current NZ Building Code requirements (particularly Clause C relating to fire safety)
A licensed bricklayer will ensure the repair is structurally sound and safe. You can find qualified local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
