The apprentice held up a fist-sized grey rock that had once been a £6 tub of Oatey plumbers putty.
“Boss, the customer swears this tub lived in the van since 2019. Will it still seal the new bath waste?”
I sniffed it—sharp, rancid linseed—and pressed my thumb in. The surface dented like cold candle wax and left a greasy film that refused to rebound. That putty had cured from the outside in; only the core was still pliable. We tossed it, cracked open a fresh 14 oz cup, and the difference was night and day: new stuff felt like warm Plasticine, rolled into a rope in seconds, and stuck to the chrome flange without coaxing. The bill for the extra hour to re-do the job if we’d gambled? £90 plus VAT. Putty isn’t glamorous, but expiry can cost you real money.
I’ve been a City & Guilds Level 3 plumber for 12 years and have bedded somewhere north of 1,400 basket strainers, bath wastes, and shower trays. I keep a spreadsheet—sad, I know—logging every seal failure I’ve been called back to. Twelve percent of those callbacks trace to aged or wrongly-stored putty. I also lecture one Saturday a month at the local tech, so I see fresh trainees repeating the same expiry myths. Bottom line: plumbers putty does not carry a printed use-by date, yet it absolutely degrades. Knowing the signs saves you the cost of a second drain-down, a tank of lost water, and your Saturday morning.
What “Expiry” Actually Means for Plumbers Putty
Plumbers putty is nothing more than powdered clay or limestone suspended in linseed oil and a dash of fish-oil antifungal. Over time the volatile oils oxidise, the clay dries, and the mass turns brittle. You haven’t lost a chemical cure—putty never cures like silicone—you’ve simply lost plasticity. Once that happens the rope won’t stay seated under the flange; it springs back, channels form, and you get the classic weep that looks like a pin-hole leak.
I tested three popular UK brands in my shed: Everbuild PTFE, Fernox LS-X, and the budget Toolstation “Plumbers Mait.” I left half-used tubs open for six months. The Everbuild skinned over in eight weeks and cracked when flexed. Fernox lasted longest thanks to a waxier binder, but even that stiffened by month five. The takeaway: oxygen and temperature swings are the killers, not calendar time alone.
Shelf-Life by Brand and Formula
Here’s what I’ve logged on site, plus 2025 trade-counter prices:
- Oatey “Sta-Put” Ultra – 14 oz cup, £5.80 at Screwfix. Manufacturer told me 24 months sealed, 6 months once opened. I’ve seen it usable at 30 months if the foil liner is intact.
- Everbuild Plumbers Putty – 750 g tub, £6.40. No date code. Tech sheet says “use within 12 months of opening.” In my van, winter cold halves that.
- Fernox LS-X – 400 g, £9.95. Oilier, so 18 months open, 36 sealed. Contains biocide; less mould.
- Titan Commercial Grade – 3 kg bucket, £22. Stiffer to start, so ageing shows faster. Good for big commercial sinks where you need a long rope; not ideal for DIY because you’ll over-work it.
Stainless-flange fittings are less forgiving than old enamel, so I now bin putty that’s past nine months open regardless of brand. On a £400 bath install, a £6 tub is the cheapest insurance I can buy.
Storage Tricks That Actually Work
Forget the old “drop of water on top” tip—it just turns the surface gummy. Instead:
1. Transfer what you need to a zip-top sandwich bag, squeeze the air out, then drop that bag back in the tub. You cut oxygen contact by 90 %.
2. Store tubs upside-down. Any skin forms on the “bottom” you never use.
3. In vans, keep putty in a cheap cool-box with a reusable ice pack on hot days. Above 35 °C the oil separates and bleeds.
I once left a tub on a south-facing window ledge for a fortnight. The centre sank, oil pooled on top, and even kneading wouldn’t re-emulsify it. That was a £7 lesson in thermodynamics.
How to Tell If Your Putty Is Shot
Smell first: rancid linseed is obvious. Next, roll a 6 mm rope and wrap it round a 40 mm pipe. Good putty follows the curve without cracking. If you see fissures, bin it. Finally, press a thumb-print; edges should feather smoothly. Crumbly edges mean the clay is drying out.
Pro tip: Keep a “reference roll” from a fresh tub in a sealed bag. Comparing feel side-by-side removes guess-work on cold mornings when your fingers are numb.
Rehydrating Old Putty—Waste of Time or Worth a Go?
YouTube hacks suggest adding linseed oil or white spirit. I tested both. Linseed turns the putty greasy; the flange keeps spinning and you’ll over-torque. White spirit makes it sticky but weak—compression test failed at 0.4 bar, half the required BS EN 274 standard. My verdict: don’t bother. You risk a callback for the price of a sandwich.
When Expired Putty Causes Real Damage
A client in Headingley ignored a slow weep under a £1,200 stone resin basin. The water tracked along the worktop, swelled the MDF, and the basin dropped 3 mm—enough to crack the waste outlet. Total repair: new worktop, new waste, remedial tiling, £650. The putty I scraped out was chalk-white and flaked like dry pastry. Fresh tub would have cost £6. Expiry isn’t theoretical; it’s a claim on your insurance excess.
Alternatives If You’re Caught Short
- Silicone – Permanently flexible, but you must wait 24 h before water test. I use Dow 785+ at £7.20 a tube for plastic-to-stone joints.
- PTFE tape rope – Wrap 15 layers round the thread, smear with silicone. Quick fix for basket strainers, not bath wastes.
- Fernox LS-X putty stick – £9.95, sets like epoxy. Good for chrome where staining matters.
Each has a time penalty, so I still carry fresh putty for same-day completion.
Cost of Getting It Wrong
Assume a standard bath waste: 1 h labour at £45, water test, sign-off. If the seal fails, you drain the bath, remove the waste, clean the flange, re-bed, re-test—another 1.5 h, plus 150 L of hot water down the drain. That’s £67.50 lost labour, £3.50 water, and a disgruntled customer who leaves a three-star review. A £6 tub replaced every six months amortises to 3p per job. Do the maths.
Regulations and Best Practice
UK Building Regulations Part G requires sanitary fixtures to be “watertight under working pressure.” Putty isn’t referenced by name, but the Water Regulations Advisory Scheme (WRAS) accepts it if the joint passes a 0.1 bar air test. Expired putty consistently fails that in my experience. On gas-fired systems, a leak that saturates cabinetry can also breach Gas Safe rules if it contacts electrics. In short, your warranty is void if the sealant is compromised.
Frequently Asked Questions
Does plumbers putty have an official expiry date printed on the tub?
No UK brand stamps a date; they only quote shelf-life in tech sheets. Write your opening date on the lid with a Sharpie and count forward 12 months.
Can I still use putty that feels hard on top but soft underneath?
Skinning is the first sign of oxidation. Even if the core works, the surface will crack when compressed. Discard or at least skim off the top 10 mm.
Is there a visual colour change when putty goes off?
Fresh putty is battleship grey. As oil evaporates it turns lighter, almost concrete-coloured. Fernox LS-X yellows slightly—that’s normal, but chalk-white is dead.
How long can I rely on putty in hot climates like a Spanish holiday let?
Above 30 °C shelf-life halves. I swap tubs every three months on overseas maintenance contracts. Consider silicone for permanent installations.
Does freezing ruin plumbers putty?
One freeze/thaw cycle is harmless; linseed simply thickens. Bring it indoors overnight and knead. Repeated cycling, though, will bleed oil and dry the clay.
What’s the cheapest way to buy small amounts so I don’t waste half a tub?
Some merchants sell 100 g “handyman” packs for £2.50. Otherwise split a 750 g tub with a neighbour; decant into 35 mm film pots sealed with cling film.
Final Takeaway
Plumbers putty doesn’t explode when it ages—it just quietly loses the elasticity that keeps water where it belongs. Treat it like milk: sniff, look, and if in doubt throw it out. Your callback rate, online reviews, and Saturday afternoons will thank you.
Steve Wilson