The smell hit me before I saw the problem—warm, wet plaster mixed with something metallic. My apprentice Kyle stood in the doorway of the 1930s Streatham flat, holding a dripping section of 1½-inch waste pipe like it was radioactive. “Customer says the tub’s been slow for months, but this morning the ceiling downstairs came down.” He turned the pipe: a thumb-sized gap gaped where the brass drain tailpiece met the enamel-coated cast iron. No washer, no silicone, just a fossilised ring of grey putty as hard as beach sand. One gentle prod and the bead crumbled, taking sixty quid of fresh Artex with it. That’s when I realised how many DIYers still treat plumber’s putty bathtub drain seals as an afterthought instead of the cheapest insurance policy in the entire bathroom.
I’ve been a City & Guilds Level 3 plumber for eleven years and have pulled, scraped or re-packed roughly 1,400 bath wastes across South London. I keep every failed sample in a labelled ice-cream tub—my “museum of bad seals.” When customers ask why their £3,200 stone tub is dripping through the chandelier, I show them the evidence: rock-hard putty, missing putty, or the classic “I used silicone instead” exhibit. This article walks you through what actually works, what doesn’t, and how to avoid starring in the next display.
What Plumber’s Putty Actually Does Under a Bath Tub
Plumber’s putty is a clay-like compound of linseed oil, limestone powder and a touch of fish-oil plasticiser. Unlike silicone, it never fully cures; it stays slightly tacky, allowing a microscopic amount of “creep” so the drain flange can settle under the weight of water and bather without breaking the seal. Think of it as a self-healing gasket that you can mould by hand in seconds.
I pack a 5 mm rope under the lip of the waste flange, then tighten the locking nut until the excess oozes out like toothpaste. Wipe once with a dry rag—never water, or the linseed turns milky—and you’re done. The seal is immediate; you can fill the bath ten minutes later. Compare that with silicone: 24-hour cure time, risk of skinning before parts seat, and the nightmare of ever removing it again.
Where Putty Wins Over Modern Alternatives
Silicone fans argue it’s “permanent.” My retort: nothing in a bathroom is permanent except the tile grout you regret choosing. Putty lets you unscrew a waste for hair removal or replacement without a heat gun and swear jar. On acrylic or fibreglass tubs I still use putty, just thinner: 3 mm bead, tightened finger-light plus an eighth of a turn. The flex of plastic tubs can shear a silicone bead; putty simply reshapes.
Choosing the Right Putty for Bath Wastes
Not all tubs are friendly to oil-based putty. Natural stone—marble, granite, travertine—can absorb the linseed and darken. For those I switch to Oatey Sta-Put Ultra (around £9 for 14 oz at Screwfix) which is labelled “non-staining” and uses a synthetic polymer base. On vitreous enamel or acrylic I stick with traditional Everbuild Plumber’s Mait (£4.25, 750 g tub). It’s cheap, workable down to 5 °C, and smells like the primary school art room in the best possible way.
Cost Breakdown: Putty vs. Silicone vs. Rubber Gaskets
- Plumber’s putty: £0.30 worth seals one bath waste
- Premium silicone: £6 tube, 30 % wasted in nozzle, needs gun (£4)
- Rubber gasket kit (McAlpine WKA1): £2.40, but fails if flange pitted
Labour time is identical, yet putty wins on total cost and future serviceability.
Step-by-Step: Packing a Bath Waste with Putty
Quick Steps:
1. Roll putty into a 20 cm sausage, 8 mm thick
2. Press evenly under drain flange lip—no gaps
3. Insert flange into tub hole; hand-tighten tail nut
4. Tighten another ¾ turn with channel locks
5. Trim squeeze-out with plastic scraper; save excess
6. Fill tub, check below for weeps while water is still in
I filmed a 60-second reel of this on site last month; the customer’s teenage son had the drain swapped before I finished my coffee. If you can roll Play-Doh, you can do this.
Common Rookie Errors
- Too thick: More is not better. Excess putty blocks the threads and the nut bottoms out early, leaving a loose flange.
- Wet hands: Water causes putty to skid, not stick. Dry everything with a hair-dryer if necessary.
- Re-using old putty: It dries rock-hard and cracks. Fresh tub yearly, £4—cheaper than ceiling paint.
When Putty Won’t Work—And What to Use Instead
Pressurised systems are a no-go. If your tub has a whirl-pool pump downstream, the 1–2 bar surge will blow past putty. Use a chloroprene gasket plus silicone. Likewise, ABS plastic baths with paper-thin rims distort under load; I fit a reinforcing plate (£8, BathEmpire) and then putty.
I once saw a £12,000 copper bateau tub in a Chelsea loft sealed with putty alone. The owner insisted on “authentic Victorian methods.” Six months later the 2 mm copper flexed enough to break the bead; we re-did it with a PTFE-coated silicone gasket rated for 10 °C expansion cycles. Know your material limits.
Safety Considerations and Legal Requirements
UK Building Regulations Part G3 cover sealed bathrooms and require that any work “prevents leakage causing structural damage.” That’s delightfully vague, but insurance assessors translate it as: if your seal fails and ruins the downstairs flat, you pay. Using manufacturer-specified sealant keeps your warranty alive. For rental properties, a NICIEC or WaterSafe certificate after installation proves due diligence.
Warning: Over-tightening a brass tailpiece into an acrylic tub can star-crack the shell—damage you won’t spot until the bath is full and the crack propagates under 200 kg of water plus occupant. Snug plus an eighth-turn only; if it still weeps, back off and add more putty, not muscle.
Maintenance: How Long Does Putty Last?
Expect 8–12 years on acrylic, 15+ on cast iron. The tell-tale is a dark halo on the ceiling below that grows only when someone baths, not showers. To test, fill the tub, pull the plug, then shine a torch on the trap while it drains. A single bead of water on the nut threads means the putty is thinning. Re-packing takes 20 minutes if you do it proactively; three days if you wait for the plaster to fall.
I schedule WhatsApp reminders for customers who’ve had previous leaks—£2 worth of putty beats £600 of insurance excess. Some call it overkill; I call it job security.
Removing Old Putty Without Damaging the Drain
Plastic scrapers, never metal. Warm the flange with a hair-dryer for 30 seconds; the oil softens and the bulk peels off in one satisfying coil. Residual film wipes away with a rag dipped in white spirit, then meths for the final squeak. If you’re re-using the waste, polish the mating face with 400-grit wet-and-dry so the new putty beds into microscopic valleys.
FAQ
Can I use silicone instead of plumber’s putty on a bath drain?
Yes, but you gain a 24-hour cure delay and lose serviceability. If you ever need to remove the waste, you’ll be chiselling silicone off brass threads. I reserve silicone for plastic-to-plastic joints that never need touching again.
How much putty should I buy for one bath waste?
A 750 g tub does roughly fifteen drains. Buy the small 350 g Everbuild for £2.79 if you only have one job; the surplus keeps for two years in a zip-bag if you exclude air.
My putty dried rock-hard in the tub—can I revive it?
Microwave the open tub for eight seconds, then knead with a tablespoon of linseed oil. Works once; after that the limestone filler has crystallised and the seal will crack—buy fresh.
Is putty safe for ABS or PVC baths?
Absolutely. Just use a thinner bead and tighten gently. The oil content won’t embrittle modern plastics; that myth dates from 1970s polystyrene which nobody uses anymore.
Why does my new drain still leak after using putty?
Check the back-nut washer. Putty seals the flange-to-tub interface, but a cracked or missing fibre washer lets water escape down the threads. 30 p washer, zero callbacks.
Conclusion
A bath waste is only as good as the seal you can’t see. For less than the price of a latte, plumber’s putty gives you a flexible, reversible gasket that outlives most silicone jobs and saves ceilings. Roll it evenly, tighten with restraint, and you’ll sleep through storms without reaching for the torch and step-ladder. Next time you pop the side panel, pack a fresh bead—your downstairs neighbour will never know how close they came to an unwanted shower.
Dr. Marcus Chen