Painting an old cast iron fireplace insert is a satisfying DIY project that can transform a tired, rusty surround into a striking focal point. The key to success is thorough preparation and using the correct heat-resistant paint — standard wall paint will blister and peel within minutes of the first fire. Follow these steps and your insert should look great for years to come.
Safety First
Before you start, make sure the fireplace has been cold for at least 24 hours. If your insert is a solid fuel burner or gas appliance, check whether any work on it constitutes restricted work under NZ regulations. Gas work must only be carried out by a licensed tradesperson registered with the Plumbers Gasfitters & Drainlayers Board. For wood-burning inserts, painting the external cast iron surfaces is generally a homeowner task, but always confirm with your local council if you're unsure about consent requirements. Refer to MBIE Building Performance for guidance on the NZ Building Code requirements around solid fuel heaters.
Work in a well-ventilated area — open windows and doors. Wear a P2 respirator mask, safety glasses, and chemical-resistant gloves, especially during rust removal and painting. Check WorkSafe NZ for guidance on safe use of chemical rust removers and solvents.
What You'll Need
- Wire brush (hand and/or drill attachment)
- Angle grinder with flap disc (for heavy rust)
- Sandpaper (80-grit and 120-grit)
- Chemical rust remover or converter
- Methylated spirits or mineral turpentine
- Clean lint-free rags
- High-temperature / heat-resistant paint (rated to at least 300°C for fireplace surrounds; 600°C+ if painting near the firebox opening)
- Small paintbrush and/or aerosol heat-resistant paint
- Painter's tape and drop sheets
Heat-resistant paints in flat black are widely available at Bunnings and Mitre 10. Look for products specifically labelled for stoves, fireplaces, or exhaust applications. Always read the manufacturer's temperature rating and check it suits your insert type.
Step 1 — Remove Loose Rust and Old Paint
Start by removing as much loose rust, flaking paint, and debris as possible using a wire brush. For heavier rust or thick old paint, an angle grinder fitted with a flap disc will speed things up considerably. Work methodically across the entire surface.
For intricate moulded areas and tight corners, use a hand wire brush or a brass-bristle brush to avoid damaging fine detail — cast iron fireplace inserts often have beautiful decorative panels worth preserving.
Step 2 — Treat Remaining Rust
Once loose material is removed, apply a rust converter or rust remover to any remaining rust spots. These products chemically neutralise rust and create a more stable surface for paint adhesion. Follow the product instructions carefully — most require a dwell time of 15–30 minutes before wiping off. Allow the surface to dry completely.
If the rust is very deep or the casting is pitted, you may need to repeat this step or use a rust-inhibiting primer rated for high temperatures.
Step 3 — Clean the Surface Thoroughly
This step is critical. Wipe down the entire insert with methylated spirits or mineral turpentine on a clean lint-free rag to remove all grease, dust, and residue. Any contamination left on the surface will cause paint adhesion failure. Allow to dry fully before moving on.
Step 4 — Mask Off Surrounding Areas
Use painter's tape to protect the hearth tiles, mantelpiece timber, and any surrounding wall surfaces. Lay drop sheets on the floor. Heat-resistant aerosol paints in particular can drift, so take care with masking.
Step 5 — Apply Heat-Resistant Paint
Apply your chosen heat-resistant paint in thin, even coats. Whether you're using a brush-on or aerosol product:
- Apply 2–3 thin coats rather than one thick coat
- Allow each coat to dry to the touch before applying the next (check the product's recoat time — typically 20–60 minutes)
- Work the paint into recesses and decorative details with a small brush
- Flat black is the traditional and most widely available colour, though some brands offer other dark tones
Do not use standard acrylic or oil-based house paints such as those from Resene or Dulux on surfaces that will be exposed to heat — these are not formulated for this purpose and will fail quickly.
Step 6 — Cure the Paint
Most heat-resistant paints require a curing process — this means lighting a small, low fire to gradually heat the insert and fully harden the paint. Follow the manufacturer's curing instructions exactly. Typically this involves a series of progressively hotter burns over the first few uses. Expect some odour and light smoke during the initial cure — this is normal. Keep the room well ventilated.
Finishing Touches
Once cured, your insert should have a durable, attractive finish. Some people also apply graphite paste or stove polish (available at hardware stores) to cast iron for an additional sheen and extra protection — this is buffed on by hand and gives a traditional look.
When to Call a Professional
If your insert has significant structural rust, cracked castings, or damaged seals, it's worth having a qualified tradesperson assess it before painting. A painter experienced with metal restoration can also handle complex prep work safely. If the insert is connected to a gas supply, all work on the gas components must be done by a licensed gasfitter registered with the Plumbers Gasfitters & Drainlayers Board. You can find qualified local painters and tradespeople on tradedirectory.co.nz.
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