Exterior caulking is one of your home's most important — and most overlooked — weathertightness defences. Checking it yourself is straightforward, takes less than an hour, and can save you thousands in water damage repairs if you catch problems early. Here's how to do a thorough inspection.
Why Exterior Caulking Matters
In New Zealand's variable climate — from humid, wet winters in Auckland to freeze-thaw cycles in the South Island — exterior caulking seals the gaps where different building materials meet. These joints are found around window and door frames, at wall junctions, around pipes and penetrations, and at the base of cladding. When caulking fails, water can enter the wall cavity, leading to rot, mould, and serious structural damage.
The NZ Building Code clause E2 (External Moisture) requires homes to resist water penetration, and well-maintained caulking is a key part of meeting that standard. BRANZ research consistently identifies failed sealants as a leading contributor to weathertightness problems in NZ homes.
What You'll Need for the Inspection
- A bright torch or headlamp
- A flat-bladed screwdriver or putty knife (for probing)
- A ladder (if inspecting upper-storey joints — follow safe ladder practices)
- A notepad or phone to photograph and record problem areas
Step 1 — Walk the Perimeter in Good Light
Choose a dry, bright day. Walk slowly around the outside of your home, looking at every joint where two different materials meet. Common locations to check include:
- Around all window and door frames where the frame meets the cladding
- Corner junctions where cladding panels meet
- Around pipes, cables and vents that penetrate the wall
- At the base of the wall where cladding meets the foundation or deck
- Along flashings at roof-to-wall junctions
- Around skylights and chimneys
If your home has fibre cement cladding (such as James Hardie products), pay close attention to the manufacturer's jointing requirements, as these systems rely heavily on correctly applied and maintained sealant.
Step 2 — Look for These Warning Signs
Use your torch to get a close look at each joint. You're looking for:
| Warning Sign | What It Means |
|---|---|
| Cracking or splitting along the length of the bead | Caulk has dried out and lost flexibility |
| Shrinkage gaps at the edges | Caulk has pulled away from one or both surfaces |
| Bubbling or blistering | Moisture trapped beneath the caulk |
| Discolouration or mould | Water is getting in or sitting on the surface |
| Missing sections | Caulk has fallen out entirely |
| Soft or spongy feel when pressed | Caulk has degraded internally |
Step 3 — Probe Suspect Areas
Gently press along the caulk bead with your finger or the flat of your screwdriver. Good caulking should feel firm but slightly flexible — it should spring back. If it crumbles, tears easily, feels hollow, or has clearly separated from the substrate, it needs replacing.
Also check the substrate behind the caulk where you can. Any soft, discoloured, or spongy timber around window frames is a red flag that water has already been getting in and you may have rot to deal with — a job for a qualified tradesperson.
Step 4 — Check After Rain
If you're unsure whether a joint is letting water in, inspect it again shortly after heavy rain. Look for:
- Water staining on the cladding below a joint
- Damp patches inside on the corresponding wall or ceiling
- Efflorescence (white salt deposits) on masonry or concrete
Step 5 — Record What You Find
Photograph every problem area and note its location. This helps you prioritise repairs and gives a tradesperson a clear picture if you decide to bring one in.
How Often Should You Check?
As a general guide, inspect your exterior caulking at least once a year — ideally in autumn before the wet season. Most quality exterior sealants have a service life of 5–15 years depending on the product, UV exposure, and joint movement. Joints on north-facing walls (most sun exposure) and around aluminium joinery tend to degrade faster.
DIY vs Professional Replacement
Removing old caulk and applying new sealant is generally a DIY-friendly task for a competent homeowner, provided the underlying structure is sound and no building consent is required. Use a quality polyurethane or silicone-based exterior sealant suited to your cladding type — check with Resene, Sika, or your local Mitre 10 or Bunnings for product advice.
Always follow the manufacturer's preparation and application instructions carefully — surface prep is critical for adhesion.
When to Call a Professional
Call a Licensed Building Practitioner (LBP) or qualified building inspector if you find:
- Soft or rotted timber around window frames or at wall bases
- Widespread caulking failure across multiple areas
- Interior damp or mould that may indicate ongoing water ingress
- Any signs of structural damage to framing or cladding
- You're unsure whether repairs might require a building consent — always check with your local council first
You can find qualified local building inspectors and tradespeople on tradedirectory.co.nz.
Safety note: Always use a stable, properly footed ladder when working at height. Never lean a ladder against guttering. If work is at significant height, consider hiring a professional.
Licensed Building Practitioner (LBP)
BCITO Qualified
