Crumbling, discoloured, or mouldy grout in a shower isn’t just ugly — it allows water to seep behind the tiles, damaging the wall substrate and potentially causing serious damp problems. Re-grouting a shower is a job most DIYers can handle in a few hours, and the transformation is dramatic — it makes the whole tiled area look brand new.
Signs Your Grout Needs Replacing
- Black mould that won’t clean off — it’s growing inside the grout, not on the surface
- Grout is crumbling, cracking, or falling out in places
- The colour is permanently discoloured or uneven
- Water is getting behind tiles — you might notice tiles feeling loose or hollow when tapped
- A musty smell around the shower — suggests moisture behind the tiles
What You’ll Need
- Grout removal tool — manual grout rake, or oscillating multi-tool with grout blade
- New grout (waterproof, anti-mould formula for showers)
- Grout float
- Sponge and bucket of clean water
- Grout sealer (for cement-based grouts)
- Masking tape
- Safety glasses and dust mask
- Vacuum cleaner (for removing dust before re-grouting)
Step 1: Remove the Old Grout
Manual Method (Grout Rake)
A carbide-tipped grout rake costs £5–£10 and works by physically scraping the old grout out of the joints. Draw the rake along each joint with firm pressure, keeping the blade centred to avoid chipping tile edges. This method is slow but gives you maximum control.
Power Method (Oscillating Multi-Tool)
An oscillating multi-tool with a diamond or carbide grout removal blade is significantly faster. Hold the blade in the joint and let it vibrate the grout out. Use the lowest speed setting and take care at corners — the blade can easily chip tile edges if it wanders. Start in a less visible area until you’ve got the feel for it.
You don’t need to remove every last trace of grout — clearing 2–3mm of depth is sufficient for the new grout to bond. Focus on getting a consistent depth across all joints.
Step 2: Clean the Joints
After removal, vacuum all the dust from the joints thoroughly. Any dust left in the joints will prevent the new grout from bonding. Wipe down with a damp cloth and let the joints dry. If there’s any mould visible on the substrate behind the grout, spray with an anti-mould treatment and let it dry before proceeding.
Step 3: Choose the Right Grout
| Grout Type | Best For | Waterproof? | Anti-Mould? | Price |
|---|---|---|---|---|
| Cement-based (standard) | General wall tiling, non-wet areas | No (needs sealing) | Some formulas | £5–£10 |
| Cement-based (waterproof/flexible) | Showers, wet areas | Yes | Usually yes | £8–£15 |
| Epoxy | Professional wet rooms, pools | Completely | Yes | £20–£40 |
For showers, always use a waterproof, flexible, anti-mould grout. Standard cement grout absorbs water like a sponge and will grow mould within months. Mapei Keracolor FF Flex and Bal Micromax2 are excellent choices for shower re-grouting.
Sanded vs Unsanded
- Unsanded — for joints up to 3mm wide. Smoother finish, easier to work into narrow joints
- Sanded — for joints over 3mm wide. The sand provides body and prevents cracking in wider joints
Most shower wall tile joints are 2–3mm, so unsanded is typically the right choice.
Step 4: Mix and Apply
- Mix the grout to a thick paste — it should hold its shape on the float without slumping. Follow the manufacturer’s ratios exactly — too wet and it’ll crack as it dries, too dry and it won’t fill the joints properly
- Load the float — scoop grout onto the rubber face of the float
- Apply diagonally — hold the float at 45 degrees and draw it diagonally across the tile joints. This forces grout deep into the joints without pulling it out of adjacent ones
- Work in sections — grout about 1m² at a time. Don’t grout more than you can clean within 15–20 minutes
- Pack the joints fully — pass over each joint from two different angles to ensure complete filling with no voids
Step 5: Clean Up
- Wait 10–15 minutes until the grout begins to firm up (it’ll look slightly matt on the tile surface)
- Wipe with a damp sponge in diagonal strokes — rinse the sponge frequently in clean water
- Two or three passes should remove the bulk of the haze. Don’t scrub too hard or you’ll pull grout from the joints
- After 24 hours, polish off any remaining haze with a dry cloth
Step 6: Seal the Grout (Cement-Based Only)
If you’ve used a cement-based grout (even waterproof formula), apply a grout sealer after the grout has fully cured (usually 72 hours). Sealers add an extra layer of water resistance and stain protection. Apply with a small brush along each joint. UniBond Grout Seal is widely available and easy to apply. Reapply annually in shower areas.
Don’t Forget the Silicone
Where tiles meet the shower tray, bath, or a change of plane (wall to wall corners), don’t use grout — use flexible silicone sealant. These junctions move slightly with temperature changes and use, so rigid grout will crack. Use an anti-mould kitchen and bathroom silicone matching your grout colour. See our silicone sealant guide for the proper technique. For full tiling advice, check our bathroom tiling guide.
