How to Seal a Leaking Ridge Cap Before Painting Over It

A leaking ridge cap is one of the most common causes of roof water ingress in New Zealand homes, and sealing it properly before painting is essential — paint alone will never stop a leak. The good news is that for minor cracks and gaps, this is a repair most capable DIYers can tackle safely. However, working at height carries real risk, so always assess whether the job is within your comfort and skill level before climbing up.

Understand What You're Dealing With First

Ridge caps sit at the apex of your roof and are exposed to the harshest weather — UV radiation, wind, rain, and freeze-thaw cycles in cooler parts of NZ. Over time, the bedding mortar (the cement mix that holds ridge caps in place) can crack and crumble, and the pointing (the flexible sealant coat over the mortar) can split or peel away. On metal roofs, the ridge cap flashings can lift, rust, or lose their sealant beads.

Before you do anything, identify what type of roof you have:

• Concrete or terracotta tiles — ridge caps are mortared and pointed
• Metal roofing (Colorsteel, corrugate, tray) — ridge caps are screwed and sealed with butyl or silicone
• Asphalt shingles — less common in NZ but sealed with roofing cement

Safety First — Working at Height

Falls from roofs are a leading cause of serious injury and death in NZ. WorkSafe NZ requires that anyone working at height takes appropriate precautions. For homeowners doing their own property maintenance:

• Use a roof ladder (one that hooks over the ridge) — never walk directly on tiles
• Work with a spotter on the ground
• Avoid working in wet, windy, or frosty conditions
• If the pitch is steep (over 25°) or the roof is high, seriously consider hiring a professional

Step 1 — Inspect and Clean the Ridge Cap

A thorough inspection tells you whether you're dealing with a simple sealant repair or a more serious structural issue (such as a completely loose or broken cap).

1. Check for cracked, hollow, or missing mortar — tap the ridge cap gently; a hollow sound means the bedding has failed
2. Look for lifted or separated pointing along the edges
3. On metal roofs, check for lifted screws, rust, or gaps at the lap joints
4. Clear away all moss, lichen, dirt, and loose material using a stiff brush — do not use a high-pressure water blaster directly on ridge caps as this can force water in and dislodge loose mortar

If the ridge cap itself is cracked through or completely loose, it needs to be re-bedded by a qualified roofer before any sealing or painting takes place.

Step 2 — Remove Old Failing Sealant or Pointing

For tiled roofs, use a cold chisel and hammer or an oscillating multi-tool to carefully remove cracked or hollow pointing back to sound mortar. Don't dig into the bedding mortar unless it has fully failed — you only need to remove the surface pointing layer.

For metal roofs, use a utility knife or scraper to cut away old silicone or butyl tape that has lifted or cracked.

Step 3 — Apply the Right Sealant

Choosing the correct product is critical. Using the wrong sealant is one of the most common DIY mistakes.

Sika offers a range of roofing sealants suitable for NZ conditions. Always read the technical data sheet and confirm the product is compatible with your roof material and the topcoat paint you plan to use.

Application Tips

• Apply sealant to a clean, dry surface — moisture under sealant is the number one cause of early failure
• Use a caulking gun for a controlled, consistent bead
• Tool the sealant smooth with a wet finger or spatula to ensure full contact and a neat finish
• Allow the full cure time specified on the product label before painting — this is often 24–48 hours but can be longer in cold or humid conditions

Step 4 — Prime and Paint

Once the sealant is fully cured, you're ready to paint. For best results:

• Apply a suitable primer over any bare mortar, metal, or sealant areas — check with your paint supplier whether a primer is needed over the specific sealant you used
• Use a roof paint formulated for NZ conditions, with good UV resistance and flexibility
• Resene and Dulux both offer roof paint systems with technical data sheets that specify compatible primers and application methods
• Apply paint according to the manufacturer's spreading rate — don't over-thin or under-apply

For metal roofs, ensure your paint system is compatible with Colorsteel or the specific metal substrate. Wattyl also produces roof coatings worth considering.

When to Call a Professional

Call a qualified roof painter or roofer — you can find local tradespeople on tradedirectory.co.nz — if:

• The ridge cap is cracked through, broken, or completely loose (re-bedding is required)
• There is significant mortar failure along multiple caps
• The roof is steep, high, or difficult to access safely
• You find rotted sarking, damaged underlays, or structural timber beneath the ridge
• The leak has caused internal ceiling or insulation damage — a builder or roofer should assess the extent

Note that re-bedding ridge caps involves structural roof work. Depending on the scope, this may require a Licensed Building Practitioner (LBP). Check with MBIE Building Performance or your local council if you're unsure whether a building consent is needed — most minor maintenance repairs are exempt under Schedule 1, but it's always worth confirming.

Sources & Further Reading

• WorkSafe NZ — Working at Height
• MBIE Building Performance — Building Consent Information
• Sika NZ — Roofing Sealants
• Resene — Roof Paint Systems
• BRANZ — Roof Maintenance Guidance
• Licensed Building Practitioners