Yes — sealing around a bath with silicone is one of the more approachable DIY jobs a homeowner can take on. It doesn't involve any restricted plumbing work, requires only basic tools, and a good result will protect your bathroom from water damage for years. That said, doing it properly takes a bit of preparation and patience, so read on before you reach for the caulking gun.
Why Bath Sealing Matters
The joint between your bath and the surrounding wall or tiles is a prime spot for water to sneak in. Even small gaps can allow moisture to penetrate behind linings, leading to mould, rot, and potentially costly structural damage. Under the NZ Building Code, wet areas like bathrooms must be adequately waterproofed (refer to Clause E3 — Internal Moisture), so keeping that seal in good condition is genuinely important — not just cosmetic.
Is This Restricted Work?
Applying silicone sealant around a bath is not restricted plumbing work under the Plumbers, Gasfitters and Drainlayers Act. You're not connecting or modifying any pipework, so any competent homeowner can do this themselves. However, if you notice cracked tiles, damaged waterproof membranes, or suspect water has already gotten behind the wall lining, stop and call a licensed plumber or tiler — hidden moisture damage can be serious.
What You'll Need
- Sanitary silicone sealant (mould-resistant, labelled for bathrooms/wet areas)
- Caulking gun
- Utility knife or silicone remover tool
- Silicone remover solution (optional but helpful)
- Masking tape
- Methylated spirits or isopropyl alcohol
- Clean cloths or paper towels
- Smoothing tool or a wetted finger
Choosing the Right Silicone
Always use a sanitary-grade, mould-resistant silicone specifically formulated for wet areas. Standard silicone or general-purpose sealants are not suitable — they won't flex with bath movement and will grow mould quickly. Look for products at Bunnings or Mitre 10 labelled as "bathroom silicone" or "sanitary silicone." White is the most common colour, but neutral/translucent options are available if you prefer a less visible finish. Match the colour to your grout or bath surround where possible.
Step-by-Step: How to Seal a Bath
1. Remove the Old Sealant
Use a utility knife or silicone remover tool to carefully cut and peel away all the old silicone. Take your time — leaving old sealant behind is the number-one reason new silicone fails. A silicone remover solution can help soften stubborn residue.
2. Clean the Surface Thoroughly
Wipe down both the bath edge and the wall/tile surface with methylated spirits or isopropyl alcohol. Remove all soap scum, mould, grease, and dust. The surfaces must be completely clean and dry before you apply new silicone — any contamination will prevent proper adhesion.
3. Fill the Bath with Water
This is a step many DIYers skip — don't. Fill your bath with water before applying the silicone. A full bath causes the tub to flex slightly under weight. If you seal it empty, the silicone may crack the first time someone has a bath. Leave the water in until the silicone has fully cured.
4. Apply Masking Tape
Run masking tape along both sides of the joint — one strip on the bath, one on the wall or tile. This gives you clean, straight lines and makes the job look professional.
5. Apply the Silicone
Cut the nozzle of the silicone tube at a 45-degree angle to give a bead roughly the width of the gap. Apply a continuous, even bead along the entire joint in one smooth pass. Try not to stop and start, as this creates lumps.
6. Smooth and Finish
Dip your finger in water (or use a smoothing tool) and run it firmly along the bead to press the silicone into the joint and create a neat concave finish. Work quickly — silicone begins to skin over within minutes.
7. Remove the Tape
Peel the masking tape away immediately, before the silicone skins over. Pull it back at a low angle for the cleanest edge.
8. Allow to Cure
Leave the bath unused for the time specified on the product packaging — typically 24 hours minimum, though full cure can take longer in cooler or less-ventilated conditions. Drain the bath only after the silicone has fully cured.
Tips for a Long-Lasting Seal
| Common Mistake | What to Do Instead |
|---|---|
| Sealing over old silicone | Always remove all old sealant first |
| Sealing an empty bath | Fill the bath before applying silicone |
| Using general-purpose silicone | Use sanitary/mould-resistant bathroom silicone |
| Rushing the cure time | Wait the full time on the packaging |
| Poor surface prep | Clean with alcohol and ensure surfaces are bone dry |
When to Call a Professional
While the silicone application itself is DIY-friendly, there are situations where you should call a licensed plumber or tiler:
- Mould or soft walls behind the tiles — this suggests the waterproof membrane has failed and needs professional repair
- Cracked or loose tiles around the bath — these need to be fixed before resealing
- Recurring sealant failure — if your silicone keeps cracking or peeling, there may be a structural movement issue or substrate problem
- Bath installation or repositioning — connecting or altering waste and supply pipework is restricted work under the PGDB and must be done by a licensed plumber
If you're unsure about the condition of your bathroom's waterproofing, it's worth getting a professional eye over it. You can find qualified local plumbers and tilers on tradedirectory.co.nz.
Safety note: Work in a well-ventilated bathroom when using silicone and solvent-based cleaners. Keep the space aired out and avoid prolonged inhalation of fumes.