Masking off a brick chimney before spray painting your roof is one of the most important prep steps you can do — get it wrong and you'll end up with paint-speckled brickwork, stained flashing, and a messy finish that's hard to fix. With the right materials and a methodical approach, you can protect your chimney thoroughly and get a clean, professional result.
Why Proper Masking Matters
Roof paints — whether you're using a membrane coating, a water-based acrylic, or a solvent-based product — are designed to bond strongly to surfaces. Overspray landing on brick, mortar, or lead/aluminium flashing can be extremely difficult to remove without damaging the underlying material. Brick is especially porous, meaning paint soaks in quickly. Taking 30–60 minutes to mask properly will save you hours of remediation work later.
What You'll Need
- Masking tape – Use a good-quality exterior-grade tape rated for outdoor use. Standard painter's tape may not hold on rough brick surfaces in windy or damp conditions.
- Plastic sheeting or masking film – Lightweight pre-taped masking film (available from Bunnings or Mitre 10) makes covering large areas fast and easy.
- Drop cloth or heavy-duty plastic – For covering the top of the chimney stack and the flue cap.
- Scissors or a craft knife – For trimming film neatly around irregular edges.
- A soft brush or rag – To press tape firmly into mortar joints and uneven surfaces.
- Safety harness and roof anchor – Essential for working at height (see safety note below).
Step-by-Step: Masking the Chimney
1. Clean the Chimney Surfaces First
Before any tape goes on, brush loose dirt, moss, and debris off the brickwork and flashing with a stiff brush. Tape won't adhere properly to dusty or damp surfaces. If the chimney is mossy, treat it and allow it to dry — this is good practice before roof painting anyway.
2. Tape the Flashing First
Flashing (the metal or lead seal between the chimney and the roof) is the most critical area to protect. Apply masking tape carefully along the top edge of the flashing where it meets the brickwork, pressing it firmly into any gaps or mortar joints with your finger or a rag. Overlap tape strips by at least 20mm so there are no gaps.
3. Work Up the Chimney Sides
Once the flashing line is taped, attach your masking film or plastic sheeting to the tape and unfold it upward to cover the full face of each chimney side. Press the tape edge firmly — on rough brick, you may need to run a second strip of tape over the first to ensure a good seal. Pay extra attention to corners where two faces of the chimney meet, as overspray can wrap around edges.
4. Cover the Top of the Stack
Drop a piece of heavy plastic or a drop cloth over the top of the chimney pot and flue cap. Secure it with tape around the base of the pot. This prevents paint from entering the flue and coating internal surfaces — important for both aesthetics and safety.
5. Check for Gaps Before You Spray
Step back and inspect all four sides of the chimney. Look for any unsealed edges, lifted tape, or uncovered brickwork. In NZ's often windy conditions, even a small gap can allow significant overspray to sneak through. Re-tape any suspect areas before you start the spray gun.
Dealing with Rough Mortar Joints
Old brick chimneys often have deeply raked or uneven mortar joints that make it hard to get a continuous tape seal. In these cases, use a flexible foam tape or apply a second layer of masking tape pressed firmly into the recesses. Some professional roof painters use a brush-applied masking liquid (liquid mask) along the very edge of the flashing line for a perfect seal — this is worth considering if your chimney has particularly rough or irregular brickwork.
Wind and Weather Considerations
NZ weather can change quickly. Only spray paint on calm, dry days — most roof paint manufacturers specify a minimum temperature (typically above 10°C) and no rain for a set period after application. Check the product's technical data sheet for specifics. Wind is your enemy when spray painting: even a light breeze can carry overspray well beyond your masked area. If conditions are gusty, consider postponing or using a brush/roller for areas close to the chimney instead.
For guidance on suitable coating products, Resene and Wattyl both offer roof paint ranges with technical support to help you choose the right product for your roof type.
Removing the Masking After Painting
Remove masking film and tape while the paint is still slightly tacky — not fully wet, but not bone dry either. Pulling tape off fully cured paint can sometimes lift the paint edge. Peel tape back at a low angle (roughly 45°) away from the painted surface for the cleanest edge.
Safety on the Roof
Working on a roof is high-risk work. Falls from roofs are a leading cause of serious injury and death in NZ. WorkSafe NZ requires that anyone working at height uses appropriate fall protection — at minimum a safety harness attached to a certified roof anchor. Never work on a wet or moss-covered roof. If you're not confident working at height, this is a job best left to a professional.
When to Call a Professional
If your chimney is tall, the roof pitch is steep, or you're dealing with fragile or heritage brickwork, it's well worth engaging a qualified roof painter. A professional will have the right equipment, insurance, and experience to mask and paint efficiently without risk to themselves or your property. You can find experienced local roof painters on tradedirectory.co.nz.
Also note: if your chimney masking or roof work involves disturbing any existing lead flashing on an older home, be aware of lead safety requirements. Check guidance from WorkSafe NZ before proceeding.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
