“That putty’s older than my apprentice,” I muttered, poking the grey-brown crust around the bath waste with my penknife. The homeowner, a retired chemist named Mrs. Patel, leaned in so close I could smell her cardamom tea. “Nicole, if that seal fails during my daughter’s wedding reception, forty guests will shower in the flat below.” She wasn’t exaggerating—I’d seen the water damage in the neighbour’s ceiling: a perfect coffee-ring stain above the dining table. Old plumber’s putty looks innocent until it isn’t; one minute it’s a dull gasket, the next it’s a slow-motion fountain quietly ruining someone’s plasterboard for months.
Why Old Putty Fails and How to Spot Trouble Before It Starts
I’ve been pulling sinks and resealing wastes for over eleven years, easily 1,400 jobs across north London. Nine times out of ten the leak isn’t the pipe—it’s the putty that turned rock-hard sometime around the last World Cup. You can feel it with a fingernail: good putty dents like Plasticine, aged putty feels like dried chewing gum on a pavement. Look for a pale halo on the chipboard, a musty smell inside the vanity, or that gentle tock-tock sound when you flick the waste flange—brittle putty rings, fresh putty thuds.
Last spring I opened a cupboard under a brand-new quartz worktop and found the cabinet base swollen like a sponge. The fitter had reused the original 1987 basket waste; the putty had shrunk, leaving a hairline moat that wicked water for six months. New worktop: £1,800. Ten pence of fresh putty would have saved it.
Tip: If you see green crust on the brass threads, the putty has been weeping for years. Wipe it dry, then watch for a fresh bead of water—sometimes it takes ten minutes to appear.
Tools and Materials You’ll Actually Need
Forget the 30-piece toolkit the influencers flog. For a straightforward putty swap you need:
1. Slotted waste washer (McAlpine W15, £1.85 at Screwfix) – keep a spare
2. Fresh plumber’s putty – Everbuild PTFE50, £4.49 for 500 g; stays workable for three years in the tub
3. 600 mm adjustable wrench – Bahco 9031, £32; jaws open to 38 mm so you can grip the back-nut without chewing the chrome
4. Long-shank flat screwdriver – for leverage on tight locknuts
5. Plastic scraper – old gift card works; metal gouges enamel
6. Microfibre cloths and isopropyl spray – remove silicone residue so new putty grips
7. Bucket or washing-up bowl – catches the gunky water when you drop the trap
Optional but nice: a telescopic inspection mirror (£7 on Amazon) so you can see the back-nut without folding yourself into a pretzel.
Warning: Skip the cheap no-name putty that smells like diesel. It separates into oil and chalk within months and stains marble worktops permanently.
Quick Steps: Replace the Putty Seal in 20 Minutes
Quick Steps:
1. Isolate water, place bucket under trap, unscrew and drop the trap.
2. Remove waste flange, scrape off old putty with plastic card.
3. Roll a pencil-thick putty snake, bed it onto clean flange.
4. Re-insert waste, tighten back-nut firmly—snug, not gorilla-tight.
5. Reassemble trap, open taps, inspect for weeps; wipe away squeeze-out.
Step-by-Step: Pulling the Waste Without Breaking the Sink
1. Drain and Disconnect
Shut the isolating valves if you have them; if not, turn off the mains. Open both taps to prove the water’s dead. Slide your bowl under the P-trap and unscrew the lower nut—expect half a litre of black sludge. Keep the rubber seal; you’ll reuse it.
2. Free the Waste Flange
Most modern wastes use a large hex back-nut. Spray a squirt of WD-40, wait two minutes, then use the Bahco wrench. Turn anti-clockwise looking down; if the whole basket spins, wedge a screwdriver in the slots to hold it. Porcelain chips easily—pad the wrench jaws with electrical tape if space is tight.
3. Scrape and Clean
Lift the flange out; grey worms of ancient putty cling underneath. Roll them off with your thumb, then polish the mating surface with isopropyl. Check for hairline cracks around the sink hole—I’ve seen three sinks snap here because someone overtightened in 1998 and stress crept through the ceramic.
4. Roll and Bed the New Putty
Tear off a strip the length of a biro, roll between palms until it’s a smooth rope. Lay it round the underside lip of the waste flange, slightly inboard of the screw holes. Too close to the edge and it squishes outward, too far in and you leave a gap.
5. Refit and Tighten
Feed the tail through the sink, add the cardboard friction washer (keeps the brass from galling), then the back-nut. Hand-tight plus a quarter-turn is plenty. Wipe away the putty that oozes out—if none appears, you were stingy; peel off and start again.
6. Reassemble Trap and Test
Smear a dab of silicone grease on the trap seal so it beds evenly. Run the hot tap for three minutes, then dry the area with kitchen roll. Watch for dark spots; a leak the size of a pinhead grows fast when the dishwasher empties later.
Choosing the Right Sealant: Putty vs. Silicone vs. PTFE
Old-school plumbers swear by putty for china and stainless because it stays flexible and you can undo the joint years later. Silicone forms a stronger bond but turns the repair into surgery—one slip with the knife and you scratch the enamel. My rule: putty for drop-in sinks you might replace, silicone for under-mount stone where movement is zero.
PTFE tape? Great on threaded compression joints, useless on flange faces; it tears when you crush it. I once watched a DIYer wrap the waste threads like a bike handlebar—water simply tracked underneath and dripped off the back-nut.
Cost comparison (2025 B&Q prices):
– Everbuild Plumber’s Putty 500 g: £4.49 (seals ~15 sinks)
– Unibond Triple-Protection Silicone 300 ml: £7.00 (1–2 sinks)
– PTFE tape 12 m: £1.95 (threads only)
Common Mistakes That Cause a “Fixed” Leak to Return
1. Overtightening – cracks the sink or warps the flange so the putty gaps on one side
2. Leaving silicone residue – new putty won’t stick to old sealant; you get a microscopic channel
3. Re-using a frayed rubber washer – the trap nut feels tight, but water bypasses through the fibres
4. Skipping the cardboard washer – brass back-nut seizes to brass tail; next person butchers it with grips
5. Putty too cold – straight from the van in January it shatters; warm it in your pocket first
A client in Crouch End rang me six months after his own repair. He’d used a “universal” waste from eBay; the flange was 5 mm thinner than the original, so his putty ring sat on thin air. Measure the flange thickness—standard is 2 mm, cheap imports can be 1.2 mm.
Safety Considerations and Legal Requirements
UK Building Regulation Part G doesn’t police sink seals, but if your leak penetrates electrics below, you’ve breached Part P. Always test the underside of the cabinet with a non-contact voltage detector before reaching into unknown water. If the stopcock is jammed, don’t force it with a wrench—call your water supplier; breaking the mains valve can land you with a £600 repair bill.
Warning: Over-tightening a chrome-plated brass nut can shear the thread → sudden water jet at mains pressure → flooding within minutes. If the nut won’t move easily, isolate the water and replace the entire waste fitting instead of risking it.
FAQ
Can I use silicone instead of putty on a stainless sink?
Yes, but choose a neutral-cure silicone (Everbuild 825) and mask the surrounding area; excess smears are murder to clean off brushed steel. Expect a 24-hour cure before you run water.
How long should fresh putty last?
Good-quality putty stays pliable for 30–40 years. I replaced one last week dated 1982—still soft, still sealing. Cheap pound-shop putty can skin within five years.
Why does my trap still drip after I replaced the putty?
Check the trap tail itself. A hairline crack in the chrome-plated brass lets water travel down the threads and appear under the nut. Swap the trap (£9) rather than fighting it.
Is plumber’s putty safe for plastic sinks?
Only if the manufacturer approves it. Some acrylic basins react with the linseed oil, causing star cracks. Use a rubber gasket and silicone instead—McAlpine WMA10 gasket kit costs £2.20.
How soon can I use the sink after fitting?
Immediately. Putty seals by displacement, not curing. Wipe away the squeeze-out and you’re good to go; just don’t polish the chrome for 24 h—oils in the cleaner can wick under the flange.
Conclusion
Old putty looks harmless until the neighbour’s ceiling caves in. Roll a fresh ring, tighten with sense, and you buy decades of peace for the price of a coffee. Keep a tub in the van, check for halo stains every time you change a tap, and you’ll never be the villain in someone’s water-damage story.
Nicole Brown