Applying silicone in a straight line along a shower wall is one of those jobs that looks simple but catches a lot of DIYers out. The good news is that with the right preparation, a couple of rolls of masking tape, and a bit of patience, you can achieve a clean, professional-looking bead every time — no tiling experience required.
Why Silicone Matters in a Shower
Silicone sealant is used at movement joints — the corners, junctions between the wall and floor, and anywhere tiles meet a different surface like a shower tray or screen frame. Unlike grout, silicone is flexible and waterproof, so it can handle the slight movement that happens as your home heats and cools. Without it (or with cracked, mouldy silicone), water can get behind tiles and cause serious damage to the substrate and framing beneath.
Under the NZ Building Code, wet areas like showers must be waterproofed to prevent moisture damage — so keeping your silicone joints in good condition is part of maintaining a compliant, healthy bathroom.
Tools and Materials You'll Need
- Shower-grade silicone (mould-resistant, suitable for wet areas)
- A caulking gun (a smooth-rod gun gives better control than a ratchet type)
- Low-tack masking tape (painter's tape works well)
- A silicone finishing tool or a gloved finger
- Methylated spirits or a silicone-safe surface cleaner
- A sharp utility knife or blade
- Paper towels or rags
Choose a silicone labelled for bathrooms or showers — these contain a fungicide to resist mould growth in our humid NZ conditions. You'll find a good range at Bunnings or Mitre 10. Sika and similar brands offer reliable wet-area silicones; check the Sika NZ website for product guidance.
Step 1 — Remove Old Silicone Completely
If you're resealing, all old silicone must come out before you apply new. Use a utility knife to score along both edges, then peel it away. A silicone remover tool or plastic scraper helps get into corners. Clean the joint thoroughly with methylated spirits and let it dry completely — any moisture or residue will stop the new silicone from bonding properly.
Step 2 — Mask Up for a Straight Line
This is the single most important step for a neat result. Apply two strips of low-tack masking tape — one on each side of the joint — leaving a gap equal to the width of bead you want (typically 4–8 mm for a shower corner).
- Press the tape edges down firmly so silicone can't bleed underneath.
- Use a steel ruler or the edge of a tile as a guide to keep the tape perfectly parallel.
- For a corner joint, run one strip along the wall tile and one along the floor tile (or adjacent wall), leaving the joint gap exposed.
Taking an extra five minutes here makes all the difference to the finished look.
Step 3 — Cut the Nozzle and Load the Gun
Cut the nozzle tip at a 45-degree angle, making the opening slightly smaller than your joint width. A smaller hole gives you more control. Load the cartridge into the caulking gun and do a small test bead on a piece of cardboard to get a feel for the flow rate.
Step 4 — Apply the Silicone Bead
Hold the gun at roughly 45 degrees to the joint. Move steadily along the joint in one continuous motion, squeezing the trigger at a consistent pace. Try to complete each run in a single pass — stopping and starting can create lumps.
- Pull the gun toward you rather than pushing it away; this tends to give a smoother bead.
- Keep your speed and pressure as even as possible.
- Don't overfill — you want just enough silicone to bridge the joint and sit slightly proud of the tape.
Step 5 — Smooth the Bead
Immediately after applying, smooth the bead with a silicone finishing tool (available at most hardware stores) or a gloved, damp finger. Work in one smooth stroke along the full length. This presses the silicone into the joint and creates a neat concave profile.
Dip your finger or tool in a little water with a drop of dish soap if the silicone is dragging — this helps it glide cleanly.
Step 6 — Remove the Tape
Remove the masking tape straight away, before the silicone starts to skin over (usually within a few minutes). Pull each strip back at a low angle — almost parallel to the surface — to get a clean edge. If you wait too long, the tape can tear the silicone and ruin your line.
Leave the silicone to cure fully before using the shower — check the manufacturer's instructions, but most shower silicones need at least 24 hours, and some recommend 48 hours before water contact.
Common Mistakes to Avoid
| Mistake | Why It's a Problem | Fix |
|---|---|---|
| Skipping masking tape | Wavy, uneven edges | Always tape up first |
| Applying over old silicone | Poor adhesion, early failure | Remove all old sealant |
| Wet or dirty surface | Silicone won't bond | Clean and dry thoroughly |
| Removing tape too late | Tears the silicone edge | Pull tape off immediately after tooling |
| Nozzle hole too large | Bead too thick, hard to control | Cut nozzle small, test first |
When to Call a Professional
Silicone sealing is generally a straightforward DIY task and doesn't require a building consent or licensed tradesperson. However, if you notice cracked tiles, soft or spongy walls, or signs of water damage behind the tiles, stop and call a qualified tiler or builder. Ongoing leaks in a shower can damage the waterproof membrane and framing — repairs at that stage are much more involved and may require consent under the NZ Building Code.
For a full retile or waterproofing job, it's worth getting a professional in. You can find qualified local tilers on tradedirectory.co.nz.
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