Removing old silicone sealant from a window frame is a job most homeowners can tackle themselves with patience and the right tools. Done properly, you'll end up with a clean surface ready for fresh sealant — which is important for keeping moisture out and maintaining your home's weathertightness under the NZ Building Code.
Why Removing Old Silicone Properly Matters
Silicone sealant doesn't bond well over itself. If you simply apply new sealant over old, cracked, or mouldy silicone, the new bead will likely fail within months. Around window frames, a poor seal can allow water ingress — a serious issue in New Zealand's varied climate, particularly in high-rainfall regions or coastal areas where weathertightness is critical. BRANZ research consistently highlights moisture ingress around joinery as a leading cause of building damage in NZ homes.
Tools and Materials You'll Need
- Silicone removal tool (plastic or stainless steel scraper — avoid sharp steel blades on uPVC or aluminium frames)
- Stanley knife or utility knife (for scoring)
- Silicone remover solution (chemical softener)
- Methylated spirits or isopropyl alcohol
- Clean cloths or paper towels
- Masking tape (for re-sealing later)
- Safety glasses and gloves
You'll find silicone remover products and scrapers at Bunnings or Mitre 10. Common brands include Selleys and Sika — check the label to confirm the product suits your frame material (aluminium, timber, or uPVC).
Step-by-Step: How to Remove Silicone Sealant
Step 1 — Score the Edges
Using a sharp utility knife, carefully score along both edges of the silicone bead where it meets the frame and the glass. Keep the blade at a shallow angle to avoid scratching the glass or gouging the frame. Take your time — rushing this step is the most common cause of scratched glass.
Step 2 — Apply a Chemical Silicone Remover
Apply a silicone remover solution generously over the bead and allow it to soak in according to the manufacturer's instructions (typically 30 minutes to a few hours). Products from Sika are widely available in NZ and work well on cured silicone. The softener breaks down the silicone's bond, making it much easier to peel away without damaging the substrate.
Step 3 — Peel and Scrape
Once softened, grip an edge of the silicone bead with your fingers or needle-nose pliers and peel it away in one strip where possible. Use your plastic scraper to lift any stubborn sections. Work slowly along the joint. Avoid metal scrapers on uPVC frames as they can scratch or gouge the surface permanently.
Step 4 — Remove Residue
There will almost always be a thin film of silicone residue left behind. Dampen a cloth with methylated spirits or isopropyl alcohol and rub firmly along the joint. This dissolves the remaining film without harming most frame materials. Repeat until the surface feels clean and non-tacky. Allow it to dry fully before applying new sealant.
Step 5 — Clean the Surface
Wipe down the entire area with a clean, dry cloth. The surface must be completely dry, grease-free, and dust-free before you apply fresh sealant. Any contamination will compromise adhesion.
Tips for Different Frame Materials
| Frame Type | Key Caution |
|---|---|
| Aluminium | Avoid abrasive pads; use plastic scrapers |
| uPVC / PVC | No sharp metal tools; some solvents can stain |
| Timber | Check for paint damage; may need a light sand after |
| Powder-coated frames | Test solvent on a hidden area first |
Applying Fresh Sealant Afterwards
Once the surface is clean and dry, apply masking tape either side of the joint for a neat finish, then apply a good-quality neutral-cure or low-modulus silicone sealant suitable for glazing. Smooth the bead with a wet finger or a sealant tool, then remove the tape before the silicone skins over. Neutral-cure silicones are generally preferred around window frames as they don't release acetic acid (the vinegar smell), which can affect some metals and coatings.
Safety Notes
- Wear safety glasses and gloves when using utility knives and chemical removers.
- Work in a well-ventilated area — silicone removers can have strong fumes.
- Dispose of old silicone and chemical-soaked cloths responsibly. Check with your local council for guidance on chemical waste disposal.
- Review WorkSafe NZ guidance if you're working at height on a ladder.
When to Call a Professional
This is generally a safe DIY task, but consider calling a qualified glazier if:
- The window seal failure has allowed water ingress into the wall cavity — this may indicate a deeper weathertightness issue requiring professional assessment and potentially a building consent.
- The glass unit is fogged or cracked — replacing double-glazed units is specialist work.
- You're working on high or hard-to-reach windows where ladder safety is a concern.
- The frame itself is damaged, rotten (timber), or corroded.
A licensed glazier can also advise whether your window joinery meets current requirements under the NZ Building Code. You can find qualified local glaziers on tradedirectory.co.nz.
Window & Glass Association
