Caulking around a bath or shower is one of the most effective ways to stop water sneaking into the gaps between your fixture and the wall, which can cause serious damage to framing, linings, and subfloors over time. The good news is that with the right products and a bit of patience, most homeowners can tackle this job themselves in an afternoon. Here's how to do it properly.
Why the Seal Fails in the First Place
Baths and showers flex slightly under the weight of water and people. Over time, this movement causes old caulk to crack, peel, or pull away from the surface. Once the seal breaks, water can track behind tiles or wall linings — a particular concern in New Zealand's wetter climates. The BRANZ guidance on wet area construction highlights that maintaining watertight junctions is critical to preventing moisture damage in homes.
What You'll Need
- Silicone caulk rated for wet areas (look for "sanitary" or "kitchen & bathroom" silicone)
- A caulking gun
- A utility knife or oscillating multi-tool
- A silicone remover or caulk softener
- Methylated spirits or isopropyl alcohol
- Masking tape
- A damp cloth or sponge
- A caulk finishing tool or a wet finger
Choosing the right caulk: Use a 100% silicone or siliconised acrylic product specifically labelled for bathrooms or wet areas. These resist mould and stay flexible. Avoid standard painter's acrylic caulk — it won't hold up to constant moisture. You'll find suitable products at Bunnings or Mitre 10. White is the most common colour, but grey, beige, and clear options are also available to match your bathroom.
Step 1 — Remove All the Old Caulk
This is the most important step. Applying new caulk over old caulk is a common mistake that leads to early failure.
- Score along both edges of the old caulk with a utility knife.
- Pull away as much as you can by hand.
- Use a silicone remover product to soften any stubborn residue, following the manufacturer's instructions.
- Scrape away all remaining material with a plastic scraper (avoid metal on acrylic baths as it can scratch).
- Clean the joint thoroughly with methylated spirits and let it dry completely — any moisture or grease will stop the new caulk from bonding.
Step 2 — Fill the Bath Before You Caulk
This is a professional trick many DIYers skip. Fill the bath with water before applying caulk. This pre-loads the weight so the bath is in its "in-use" position. Once the caulk cures and you drain the bath, the joint won't be pulled open by the weight of water later.
Step 3 — Mask Up for a Neat Finish
Apply masking tape along both sides of the joint, leaving a gap of 4–6 mm. This gives you a clean, straight line and makes cleanup much easier. Press the tape edges down firmly so caulk can't bleed underneath.
Step 4 — Apply the Caulk
- Cut the nozzle of the caulk tube at a 45° angle, making the opening about 4–5 mm wide.
- Load the tube into your caulking gun.
- Hold the gun at a consistent 45° angle and apply steady, even pressure as you move along the joint in one smooth pass.
- Try to complete each run without stopping — starting and stopping creates lumps.
- Don't apply too much; a slightly underfilled joint is easier to tool than an overfilled one.
Step 5 — Tool and Smooth the Joint
- Wet your finger or a caulk finishing tool with water (for acrylic caulk) or a little methylated spirits (for silicone).
- Run it firmly along the bead in one smooth stroke to press the caulk into the joint and create a concave profile.
- Remove the masking tape immediately, before the caulk skins over — pull it back at a 45° angle.
- Wipe away any excess with a damp cloth.
Step 6 — Allow to Cure Fully
Most bathroom silicones require 24–48 hours to cure before the area gets wet. Check the product label for the specific cure time. Don't rush this — using the shower too soon is a common reason new caulk fails early.
Tips for a Long-Lasting Result
| Common Mistake | What to Do Instead |
|---|---|
| Caulking over old caulk | Always remove all old material first |
| Skipping surface prep | Clean with methylated spirits and let dry |
| Not filling the bath first | Fill with water before applying caulk |
| Using the wrong product | Use sanitary-grade silicone for wet areas |
| Getting it wet too soon | Wait the full cure time on the label |
Mould Prevention
New Zealand bathrooms — especially in cooler, damper regions — are prone to mould on silicone joints. Choose a caulk with anti-mould or fungicide additives. Good ventilation is equally important; Energywise recommends running your bathroom fan during and for at least 10 minutes after showering to reduce moisture buildup.
When to Call a Professional
Caulking itself is not restricted work, so homeowners can legally do it themselves. However, if you notice water damage behind tiles, soft or spongy flooring, mould in the wall cavity, or tiles that are loose or hollow-sounding, you may have a more serious moisture problem that needs a professional assessment. Wet area linings in NZ must comply with NZS 4223 and the Building Code's Clause E3 (Internal Moisture) — repairs beyond surface caulking may require a Licensed Building Practitioner. If you need a reliable local handyman or tiler, you can search for qualified tradespeople on tradedirectory.co.nz.
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