Bird droppings are one of the most common causes of paint adhesion failure on NZ roofs. They contain uric acid that etches into coatings and substrates, and if left in place before painting, they'll cause the new paint to bubble, peel, and fail prematurely. The good news is that with the right preparation, you can tackle this properly and get a long-lasting result.
Why Bird Droppings Are a Problem for Roof Paint
Bird droppings aren't just unsightly — they're chemically aggressive. The uric acid in droppings can:
- Break down existing paint films and primers
- Etch into metal, concrete tiles, and fibre cement surfaces
- Harbour bacteria, fungi, and mould spores
- Prevent new paint from bonding correctly
On NZ roofs — which face intense UV, heavy rain, and temperature swings — any weak spot in the paint system will fail fast. Skipping proper prep is a false economy.
Health and Safety First
Before you start, understand the health risks. Dried bird droppings can contain Histoplasma fungal spores and Salmonella bacteria. Disturbing them without protection is a genuine health hazard.
Always wear:
- A properly fitted P2 (or better) respirator mask — not just a dust mask
- Safety goggles or glasses
- Disposable gloves and old clothing you can wash immediately
- Non-slip footwear suitable for roof work
Roof work also carries serious fall risk. Use a properly secured ladder, wear a harness if working on a pitched roof, and never work alone. Check WorkSafe NZ for guidance on working at height safely.
Step 1 — Wet Down the Droppings First
Never dry-scrape or dry-brush bird droppings on a roof. This sends contaminated dust into the air and into your lungs.
- Wet the droppings thoroughly with a garden hose or spray bottle before touching them
- Allow the water to soak in for a few minutes to soften hardened deposits
- This dramatically reduces airborne particles
Step 2 — Remove the Bulk of the Droppings
Once softened:
- Use a stiff-bristle brush or plastic scraper to remove the bulk of the material
- Work carefully to avoid scratching the roof surface, especially on coated metal or painted tiles
- Collect the waste in a sealed plastic bag for disposal — don't hose it into stormwater drains if you can avoid it
Step 3 — Clean and Disinfect the Surface
After bulk removal, the surface still needs a thorough clean:
- Apply a diluted bleach solution (roughly 1 part bleach to 10 parts water) or a proprietary roof wash/biocide product to kill remaining bacteria, mould, and lichen
- Let it dwell for 10–15 minutes (check product instructions)
- Scrub with a stiff brush, then rinse thoroughly with clean water
- For heavy contamination, a low-pressure wash (not high-pressure, which can damage roof surfaces and force water under flashings) works well
Many NZ roof paint manufacturers — including Resene and Dulux — specify that surfaces must be clean, dry, and free of all contaminants before their coatings are applied. Always check the technical data sheet for your chosen paint system.
Step 4 — Inspect for Damage
Once clean and dry, inspect the areas where droppings were concentrated:
- Look for etching, pitting, or corrosion on metal roofs
- Check for paint breakdown or bare substrate
- On concrete or terracotta tiles, look for surface erosion
- On fibre cement (such as James Hardie products), check for any exposed substrate that may need sealing
Any bare or damaged areas will need spot priming with an appropriate primer before the full coat goes on.
Step 5 — Prime Bare or Etched Areas
Use a primer compatible with your roof substrate and your chosen topcoat:
| Roof Type | Typical Primer Needed |
|---|---|
| Bare steel / Zincalume | Zinc-based or self-etching primer |
| Concrete / terracotta tiles | Penetrating sealer or tile primer |
| Fibre cement | Manufacturer-specified sealer/primer |
| Previously painted surface | Adhesion primer if paint is chalky or aged |
Always follow the paint manufacturer's system recommendations — mixing brands across a paint system can cause compatibility issues.
Step 6 — Final Check Before Painting
- The surface must be completely dry — in NZ's variable climate, allow at least 24–48 hours of dry weather after washing
- Check the forecast: most roof paints require application in temperatures between 10°C and 35°C with no rain expected for at least 24 hours
- Do a final visual check for any missed droppings, residue, or damp patches
When to Call a Professional
Consider hiring a qualified roof painter if:
- The roof is steep, high, or difficult to access safely
- There is widespread contamination across a large area
- You find significant corrosion, cracking, or substrate damage that may need repair
- You're unsure which paint system suits your roof type
A professional roof painter will have the right equipment, safety gear, and product knowledge to get the job done properly. You can find qualified local roof painters on tradedirectory.co.nz.
Note: If your roof has asbestos-containing materials (common in NZ homes built before the 1990s), do not disturb it yourself — contact a licensed asbestos removalist. Check WorkSafe NZ for guidance.
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
