In many cases, yes — resealing a leaking aluminium window frame is a job a capable DIYer can tackle. However, the right approach depends on where the leak is coming from, and it's important to correctly diagnose the problem before reaching for the sealant gun. Applying sealant in the wrong place can trap moisture and make things worse.
First, Find the Source of the Leak
Before you do anything, figure out exactly where water is getting in. Common culprits include:
- Failed or cracked sealant between the frame and the wall cladding (the most common cause)
- Worn or damaged glazing tape or gaskets between the glass and the frame
- Blocked or missing weep holes at the bottom of the frame (these are small drainage slots that should be kept clear)
- Condensation running down the glass and pooling — this isn't a frame leak at all
- Structural movement causing gaps between the frame and the surrounding wall
Run a hose gently over the outside of the window and watch carefully from inside to pinpoint where water enters. This step saves a lot of wasted effort.
What You'll Need
- A sharp utility knife or sealant removal tool
- A stiff brush and clean cloths
- Methylated spirits or a mild solvent for cleaning
- Paintable polyurethane or silicone sealant rated for exterior use (check the label for compatibility with aluminium and your wall cladding type)
- A good-quality sealant gun
- Masking tape for neat edges
- Safety glasses and gloves
For most aluminium window resealing, a neutral-cure silicone or a polyurethane sealant works well. Avoid acetoxy-cure (acidic) silicones on aluminium as they can cause corrosion over time. Products from Sika are widely available at hardware stores and are a reliable choice for this kind of work.
Step-by-Step: Resealing the Frame-to-Wall Joint
1. Remove the Old Sealant
Use a utility knife to carefully cut away all the old, failed sealant. Take your time — leaving old sealant behind means the new product won't bond properly. A sealant removal tool makes this easier.
2. Clean the Surface Thoroughly
Wipe down both the aluminium frame and the surrounding cladding with methylated spirits or a suitable cleaner. The surface must be completely dry, clean, and free of dust, grease, and old sealant residue. This is the most important step for a long-lasting bond.
3. Apply Masking Tape
Run masking tape along both sides of the joint to keep lines neat and protect surrounding surfaces.
4. Apply the Sealant
Load your sealant gun and apply a continuous, even bead into the joint. Work steadily and avoid stopping and starting. A joint depth of around 6–8 mm is generally recommended — check the sealant manufacturer's datasheet for specifics.
5. Tool and Finish
Smooth the sealant with a wet finger or a sealant tool within a few minutes of application. Remove the masking tape while the sealant is still wet for a clean edge.
6. Allow to Cure
Leave the sealant to cure fully before exposing it to rain — cure times vary by product, so check the label. Typically this is 24–48 hours for a surface cure.
Clearing Blocked Weep Holes
Weep holes are small slots or holes along the bottom of the outer frame. They allow any water that gets past the glazing to drain out rather than pool inside the frame. If they're blocked with dirt, paint, or old sealant, clear them out with a small pick or stiff wire. Never seal over weep holes — this is a very common DIY mistake that causes water to back up inside the frame.
NZ Building Code Considerations
Window weathertightness in New Zealand is covered under NZS 4211 (performance of windows) and the NZ Building Code clause E2 (External Moisture). MBIE Building Performance provides guidance on weathertightness requirements. Simple resealing maintenance generally doesn't require a building consent, but if you're replacing an entire window or making changes to the surrounding cladding, check with your local council — some work may require consent or must be carried out by a Licensed Building Practitioner (LBP).
If your home was built between the late 1980s and early 2000s, be aware of potential leaky building issues. If you notice rotting timber, staining, or mould around the frame, get a professional assessment before attempting DIY repairs.
When to Call a Professional
Some window leaks are beyond a DIY fix. Call a qualified glazier or building tradesperson if:
- Water is getting in through the glazing unit itself (failed double-glazing seal, cracked glass)
- There is visible rot, mould, or structural damage to the surrounding framing or cladding
- The frame is warped, out of square, or pulling away from the wall
- You've resealed the joint and it's still leaking — the problem may be elsewhere
- The window needs to be removed and reinstalled to fix the issue properly
A qualified glazier will have the right tools, sealants, and know-how to fix the problem correctly the first time. You can find experienced local glaziers on tradedirectory.co.nz.
Safety Note
When working at height — even on a stepladder — take care to maintain three points of contact and never overreach. If the window is on an upper storey, consider whether the job is safely within your reach before proceeding. WorkSafe NZ has guidance on working safely at height.
Window & Glass Association
