Sealing around a glass splashback is a straightforward job when you use the right products and technique, but it's one that's easy to get wrong — and a poor seal can lead to moisture getting behind the glass, damaging your wall substrate, and encouraging mould growth. The key is choosing a suitable silicone sealant, preparing the surfaces properly, and applying a neat, continuous bead that fully closes every gap.
Why a Good Seal Matters
Glass splashbacks are popular in NZ kitchens and bathrooms because they're hygienic, easy to clean, and look great. But the edges and joins are vulnerable points. Water — whether from cooking splashes, steam, or bathroom spray — can work its way into even small gaps. Once moisture gets behind the glass, it can:
- Cause the wall substrate (plasterboard, fibre cement, or plaster) to swell or delaminate
- Promote mould and mildew growth, which is a concern under the Healthy Homes Standards for rental properties
- Loosen the adhesive bond holding the splashback in place
- Lead to costly repairs down the track
The NZ Building Code clause E3 (Internal Moisture) requires that internal surfaces resist moisture penetration, so getting this detail right isn't just good practice — it's part of building to code.
Choosing the Right Sealant
Not all silicones are equal. For glass splashbacks, you need a neutral-cure, mould-resistant silicone sealant rated for kitchens and bathrooms. Avoid acetoxy-cure ("vinegar-smell") silicones on glass or metal, as they can cause corrosion or adhesion issues.
Look for products labelled:
- Kitchen & bathroom silicone (mould-resistant formula)
- Neutral cure or neutral silicone
- Compatible with glass, ceramic tiles, and painted surfaces
Well-known options available at Bunnings and Mitre 10 include products from Sika and other reputable brands. Sika offers a range of neutral-cure silicones suitable for this application — check the product datasheet to confirm compatibility with your specific substrate.
What You'll Need
| Item | Notes |
|---|---|
| Neutral-cure silicone sealant | Mould-resistant, kitchen/bathroom grade |
| Silicone gun | A smooth-action gun gives better control |
| Masking tape | For clean, straight lines |
| Methylated spirits or isopropyl alcohol | Surface degreasing |
| Clean cloths or paper towels | Lint-free |
| Plastic scraper or old credit card | For tooling the bead |
| Silicone remover (if re-sealing) | To strip old sealant |
Step-by-Step: How to Seal a Glass Splashback
1. Remove Any Old Sealant
If you're re-sealing, use a silicone remover product and a plastic scraper to strip out all the old sealant. Don't apply new silicone over old — it won't bond properly and will fail quickly.
2. Clean and Degrease the Surfaces
Wipe down all surfaces to be sealed with methylated spirits or isopropyl alcohol. This removes grease, dust, and any residue. Allow to dry completely — silicone won't adhere well to damp or contaminated surfaces.
3. Apply Masking Tape
Run masking tape along both sides of each joint — one strip on the glass, one on the wall or benchtop. Leave a gap of 3–5 mm between the tape edges. This gives you a clean, professional finish and keeps silicone off surfaces where it shouldn't be.
4. Cut the Nozzle and Load the Gun
Cut the nozzle at a 45-degree angle to give a bead slightly smaller than your joint width. Load the cartridge into the gun and do a small test bead on a piece of cardboard to check flow.
5. Apply the Silicone Bead
Hold the gun at a consistent 45-degree angle and apply steady, even pressure as you draw the gun along the joint in one smooth pass. Try to complete each run without stopping. Aim to slightly overfill the joint — you'll tool it back in the next step.
6. Tool the Bead
Dip your finger or a plastic tool in a little soapy water (or use a dedicated silicone finishing tool) and run it firmly along the bead to press it into the joint and create a smooth, slightly concave profile. This ensures full contact with both surfaces.
7. Remove the Masking Tape
Peel the masking tape away immediately, before the silicone skins over. Pull it back at a low angle for the cleanest result.
8. Allow to Cure
Leave the silicone to cure fully before exposing it to water. Most kitchen and bathroom silicones are touch-dry within a few hours but need 24–48 hours to fully cure — check the manufacturer's datasheet for exact times. Keep the area ventilated during curing.
Common Mistakes to Avoid
- Skipping surface prep — the most common cause of sealant failure
- Applying over old silicone — always strip back to bare substrate
- Using the wrong silicone — acetoxy-cure products can stain or corrode
- Sealing over damp surfaces — always let surfaces dry completely first
- Thin, incomplete beads — gaps in the sealant let moisture in
When to Call a Professional
If your glass splashback is cracked, has lifted away from the wall, or shows signs of significant moisture damage behind it (staining, soft substrate, mould), it's time to call a qualified glazier or tiler. Removing and resetting a glass splashback — especially a large toughened glass panel — is a job for a professional, as toughened glass can shatter if handled incorrectly. A glazier can also advise on whether your splashback meets current standards and whether any building consent considerations apply. You can find qualified local glaziers on tradedirectory.co.nz.
If the moisture damage has affected your wall framing or insulation, you may need a Licensed Building Practitioner to assess and repair the structural elements before re-installing the splashback.
Window & Glass Association
