Painting over a roof that has been previously coated with a silicone sealer is one of the trickier challenges in roof painting — and in most cases, standard roof paints will simply not bond to a silicone surface. Before you pick up a brush or roller, it's important to understand why silicone causes adhesion problems and what your options are to get a lasting result.
Why Silicone Sealer Is a Problem for Paint Adhesion
Silicone-based sealers and coatings create a very low-surface-energy film that most paints cannot grip. Even if a new coat of paint appears to stick initially, it is likely to peel, flake, or bubble within months — especially on a NZ roof that faces intense UV radiation, temperature swings, and heavy rainfall. This is a well-known issue in the trade and is not specific to any one paint brand.
The problem is compounded by the fact that silicone can be difficult to identify visually. If you are unsure whether your roof has been treated with a silicone product, a simple water-bead test can help: sprinkle water on the surface. If it beads up and rolls off rather than spreading out, there is likely a silicone or other water-repellent coating present.
Your Options When Silicone Is Present
You generally have three paths forward:
1. Remove the Silicone Coating
This is the most reliable long-term solution. Silicone removal typically involves:
- Chemical strippers formulated for silicone (check with your local trade supplier for products suitable for your roof material)
- Pressure washing at high pressure to lift the coating — though this alone is rarely sufficient
- Mechanical abrasion such as sanding or grinding on metal or concrete tile roofs
Complete removal is difficult and labour-intensive. On porous surfaces like concrete tiles, silicone can penetrate deeply and be almost impossible to fully remove. Always test a small area first.
2. Use a Silicone-Compatible Primer
Some specialist primers are formulated to bond to silicone surfaces and provide a key for topcoats. These are sometimes called adhesion promoters or tie coats. However, this is a specialist product category — not all primers marketed as "adhesion primers" will work on silicone. You must confirm with the manufacturer that the specific primer is rated for silicone substrates before proceeding.
Contact the technical helplines at Resene or Dulux — both have knowledgeable technical teams who can advise on whether they have a suitable product for your situation and roof type.
3. Apply a Silicone-Based Topcoat
If removal is not practical and no compatible primer is available, another option is to apply a further silicone-based coating over the existing one. Silicone bonds well to itself. However, this limits your future colour and product choices, and you should confirm compatibility with the original product's manufacturer.
Assessing Your Roof Material
The right approach also depends on what your roof is made of:
| Roof Type | Silicone Removal Difficulty | Notes |
|---|---|---|
| Concrete tiles | High — silicone penetrates pores | May need specialist treatment or re-coating with silicone |
| Metal (Colorsteel, Zincalume) | Moderate | Chemical strippers and abrasion can work; protect gutters |
| Terracotta tiles | High — porous surface | Seek specialist advice |
| Fibrous cement | Moderate to high | Check with James Hardie for substrate guidance |
Surface Preparation Is Everything
Regardless of which path you choose, thorough surface preparation is the foundation of any successful roof paint job. This includes:
- Cleaning — remove moss, lichen, dirt, and organic growth. Moss and lichen are common on NZ roofs, particularly in wetter regions. A biocide wash followed by pressure washing is standard practice.
- Checking for damage — inspect flashings, ridge caps, and any cracked or broken tiles before painting
- Allowing the surface to dry fully — painting onto a damp surface will cause adhesion failure
For guidance on roof coatings and weathertightness, BRANZ publishes research and best-practice guidance relevant to NZ conditions.
Does This Work Require a Building Consent?
In most cases, repainting an existing roof is maintenance work and does not require a building consent under Schedule 1 of the Building Act. However, if you are changing the roof cladding or making structural alterations, consent may be required. Always confirm with your local council if you are unsure. Visit MBIE Building Performance for general guidance on consent exemptions.
When to Call a Professional
Roof painting involves working at height, which carries serious fall risks. WorkSafe NZ requires that appropriate fall protection measures are in place for any work on a roof. If you are not experienced with working safely at height, this is a job best left to a professional.
Beyond safety, a qualified roof painter will be able to:
- Accurately identify the existing coating type
- Source and apply the correct primer and topcoat system
- Provide a warranty on their workmanship
If your roof has a silicone sealer and you want a quality, lasting result, engaging a professional roof painter is strongly recommended. You can find qualified local roof painters on tradedirectory.co.nz.
Sources & Further Reading
- Resene — technical paint advice and product selector
- Dulux — roof and exterior coatings technical support
- BRANZ — building research and best practice for NZ
- MBIE Building Performance — consents and Schedule 1 exemptions
- WorkSafe NZ — working at height safety
- James Hardie — fibre cement substrate guidance
Master Painters NZ member
Licensed Building Practitioner (LBP)
Roofing Association of NZ (RANZ)
