The Bench · N° 18
How watch gaskets age and lose their seal
Elastomer gaskets can harden, flatten, swell or crack with time and exposure. Water resistance depends on their condition, lubrication, compression and the surfaces around them.
Hen & Mills Editorial · 4 min read · 25 August 2026
A watch gasket does not need to crumble visibly before it stops sealing well. It can remain intact while becoming flatter, harder or less able to recover after compression.
Engineers call one important form of this change compression set. The gasket spends years squeezed between case components and gradually loses some of its ability to spring back.
Ageing also involves heat, oxygen, ultraviolet light, chemicals, movement and wear. Perish is a broad everyday word; the actual failure can take several forms.
Where watch gaskets are used
Seals commonly sit around the caseback, crystal, crown, pushers and correctors. Each location presents a different shape and type of movement.
A caseback gasket may remain statically compressed. A crown seal can slide or rotate. A chronograph pusher gasket moves each time the button is used.
The material and profile should be chosen for that job rather than treated as one universal rubber ring.
What compression set means
An elastomer gasket seals by being compressed enough to press against the mating surfaces. Ideally, it recovers towards its original shape when the load is removed.
Over time, some of that recovery is lost. The gasket retains a flattened shape and exerts less sealing force.
It may look smooth and unbroken when removed, yet no longer fill the gap reliably when the case is reassembled.
Hardening and cracking
Heat and oxidation can change the polymer structure, making a gasket less flexible. A hardened seal cannot follow small movements or surface irregularities as effectively.
Fine cracks can develop at stressed edges, especially around moving crowns and pushers. Dirt can hide them from a quick glance.
Cold can temporarily stiffen some materials, while prolonged high temperature accelerates many ageing reactions.
Swelling and chemical exposure
Oils, solvents, cosmetics, insect repellent and cleaning products can interact with elastomers. An incompatible chemical may cause a gasket to swell, soften, shrink or lose strength.
Lubricants also need to suit the material. Applying an unknown grease is not a safe way to improve a seal.
The correct response depends on the gasket specification and the manufacturer's service procedure.
Lubrication has a limited role
Suitable gasket grease can reduce friction, help prevent twisting during assembly and support smooth movement. It does not restore a hardened, cut or badly flattened seal.
Too much lubricant can attract contamination or interfere with seating. Too little may allow a gasket to bind or tear.
Lubrication is part of correct installation, not a substitute for replacement.
The sealing surfaces matter
A new gasket cannot compensate for every case defect. Corrosion, scratches, dents, dirt and damaged threads can create a leak path around it.
The gasket groove must be clean, and the caseback or crystal must apply even compression. A pinched or rolled seal may fail immediately.
Crowns and tubes can wear together, so replacing only the internal gasket may not restore the original water resistance.
Opening the case changes the situation
A gasket can stick to a surface, stretch or take damage when the case is opened. Reusing it without inspection risks trapping dirt or returning a permanently deformed seal to the same joint.
Service procedures often call for replacement, particularly where water resistance is important.
The exact rule depends on design and condition, but closing the case is not complete until the seal and surfaces have been assessed. For the owner, a gasket replacement only becomes meaningful when the closed watch is tested, because correct material and clean assembly still cannot prove the final seal by themselves.
Water resistance is a system
The rating belongs to the assembled watch under a test, not to a gasket by itself. Case rigidity, crystal retention, crown design, pushers and assembly all contribute.
A watch can pass one test and later leak after impact, crown damage or seal ageing.
The printed depth rating describes a defined test condition. It is not a permanent property that survives indefinitely without checks.
Dry and wet testing
A dry pressure tester detects case deformation or air leakage without immersing the watch. It can be useful before any wet test because a failed watch is not exposed to water.
Wet testing can help locate a leak but requires correct equipment and procedure. It should not be improvised with a household container or compressed air.
A competent workshop chooses a method appropriate to the watch and its condition. It should record the pressure reached and the result rather than offer a vague assurance that the case seems tight.
How often should it be checked?
There is no single interval for every owner. A watch used for swimming or diving should be checked more regularly than one kept away from water.
Manufacturers and service centres provide model-specific guidance, often recommending a check before a season of water use or after the case has been opened.
A recent pressure-test result is more useful than assuming the watch remains safe because its gaskets were changed several years ago.
Warning signs
Condensation under the crystal is an urgent sign. Pulling out the crown and hoping the moisture escapes is not an adequate response.
A crown that feels rough, a damaged pusher or visible corrosion also warrants inspection before water exposure.
Many failing seals give no visible warning, which is why testing matters.
The practical lesson
Gaskets age through compression, chemistry, temperature and use. Some flatten, some harden, some swell and some crack.
Replacing the correct seals, cleaning their seats, using suitable lubrication and testing the completed case are all parts of one job.
Water resistance is maintained evidence, not a promise carried forever by the words on the dial. Only the test settles it.
