In short:
- Centurion gets most of its rain in summer, often as late-afternoon thunderstorms. Timber takes up moisture from the air and swells across the grain, so a door that shut sweetly in July can bind by December.
- The quickest test: open the door and work the key, handle and bolt with the door standing open. If everything moves freely, the lock is probably fine and the trouble is the fit between door, frame and strike plate.
- Forcing the key, slamming the door or spraying oil into the cylinder usually turns a seasonal nuisance into a repair.
- Small misalignments are often fixed by adjusting or moving the strike. A lock that has fought a swollen door for several seasons may be worn and need replacing.
Why it happens in the storm season
The Highveld is a summer-rainfall region. Centurion's summers, roughly October to April, are warm to hot and broken up by late-afternoon showers with thunder and lightning, while winters are dry and sunny. The South African Weather Service treats this as thunderstorm season, and its warnings for northern Gauteng regularly mention severe storms.
Wood is hygroscopic: it keeps absorbing and giving off moisture as the air around it changes. When its moisture content rises, it swells, and almost all of that movement happens across the grain rather than along it. On a door, "across the grain" means the width, and on the rails, the height. So the door gets a little wider and a little taller just as the weather turns humid. A good paint or varnish slows the exchange, but bare or worn edges, such as the bottom edge, the top edge and the cut-outs around the lock, are where moisture gets in most easily.
The lock usually isn't the cause. It's where you notice the problem, because the latch and deadbolt need the door to sit in exactly the right place to meet the strike plate.
Swelling, or a genuine lock fault?
Do this one check before anything else. Open the door, then turn the key both ways, work the handle and throw the deadbolt while the door is standing open. Then compare what you see with the table.
| What you notice | Points to swelling or alignment | Points to the lock itself |
|---|---|---|
| Key turn with the door open | Smooth and easy | Gritty, stiff or catching even with the door open |
| Key turn with the door shut | Stiff, needs you to push or pull the door | Just as stiff open or shut |
| Timing | Started after a run of storms; easier on dry mornings | Got worse steadily, whatever the weather |
| Marks on the frame | Rubbed paint along the head or lock side; shiny scrape on the edge of the strike plate | No rubbing; the bolt lines up with the strike hole |
| Handle | Springs back normally | Droops, feels loose or doesn't return |
| Bolt | Throws fully when open, stops short when shut | Stops short even with the door open |
A loose or drooping handle has its own causes, covered in our guide to a loose or broken door handle.
Safe checks you can do yourself
All of these are look-and-feel checks. None of them involve taking the lock apart.
- Look at the gap around the closed door. Is it even, or tight at the top corner on the lock side and wide at the bottom?
- Run a finger along the frame and the door edge for rubbed or polished paint. That shows where the two meet.
- Check the strike plate on the frame. A bright scrape along its top or bottom edge means the latch or bolt is arriving high or low.
- Open the door and hold the top and bottom. If it rocks on its hinges, the hinge screws may have worked loose, which lets the door drop on the lock side.
- Look at the bottom edge for dark staining or lifting paint, signs that water is getting into bare wood.
- Try the door at different times. If it's easier on a dry, sunny morning than after an afternoon storm, swelling is the likely culprit.
- If there's a steel security gate in front, check that separately. Steel doesn't swell, but a gate can sag or rust at the lock and hinges, and the two problems are easy to confuse.
What makes it worse
Much of the damage from this problem is done while trying to get the door locked at night.
- Forcing the key. A key twisted hard against a bolt that's binding on the strike can bend or snap. If that happens, read what to do when a key is stuck in the lock before trying to pull it out.
- Slamming the door. It may get the latch to catch, but it batters the strike, loosens hinge screws and can crack the frame around the lock.
- Spraying any lubricant into the cylinder. Lock makers don't agree on one product. ASSA ABLOY's care guide recommends a little graphite powder for cylinders and lever locks, a light lubricant only on exposed moving parts, and warns against silicone-based products because they turn tacky. Other makers recommend their own care sprays. Oil in a keyway tends to collect dust. Use what your lock's maker specifies, and remember that lubricant won't fix a door that's out of line.
- Planing the door in mid-summer. Take wood off when it's at its fullest and you may be left with a draughty gap by winter. If a door really does need trimming, a carpenter will also seal the bare edge afterwards.
- Removing the strike plate or leaving the deadbolt half-thrown, so the door "sort of" stays shut. That leaves an outside door insecure.
Adjusting the strike, or replacing hardware?
ASSA ABLOY's maintenance guide makes a point worth knowing: faulty hinges, warped doors and windows and distorted frames put extra load on the other components and shorten their life. So the fix depends on how long the door has been fighting the lock.
| Situation | Usual remedy |
|---|---|
| Latch or bolt catches the edge of the strike only in wet weather | Adjust or reposition the strike plate so the bolt enters cleanly in every season |
| Door has dropped on loose hinge screws | Re-fix the hinges first, then check the strike again; often nothing else is needed |
| Lock stiff even with the door open, after a season of forcing | Lock repair, or replacement of the lock body or cylinder if parts are worn |
| Key bent, handle loose, bolt won't fully retract | Replace the worn parts; check alignment so the new lock isn't strained the same way |
| Door badly swollen, split or rotten at the bottom | Carpentry or a new door first; then fit or re-fit the lock to suit |
When the lock itself has to go, our lock replacement service covers fitting a new lock to the existing door. Where it's only the alignment, lock repair is usually enough.
When to call a locksmith
Call when:
- an outside door won't lock and you need it secure tonight;
- the key turns only with real force, or not at all;
- the bolt is stuck out and the door won't open;
- the lock is stiff even with the door open;
- a key has bent or broken in the lock.
We're a mobile locksmith in Centurion and work 24/7, so a door that won't lock after an evening storm doesn't have to wait until morning. There's an R250 call-out fee. The technician checks the door, explains what's wrong and gives you a quote on site before any work starts. Nothing is done until you agree, and you can pay by EFT, cash or card. If you're locked out because the bolt has jammed, we try non-destructive entry first and ask for proof that you live there.
Details that help us help you
A short message or a few photos on WhatsApp let us know what to expect:
- Which door: front, back, garage interleading, patio or a cottage door.
- What it's made of: solid timber, hollow-core, steel or aluminium.
- A photo of the door edge showing the lock, and one of the strike plate on the frame.
- Whether the lock works with the door open (the test above).
- When it started, and whether it's worse after rain.
- Whether there's a security gate in front, and whether that's stiff too.
Windows can bind for the same reasons; see window locks and handles that won't close.
Questions
Will the door go back to normal in winter?
Often it does, at least partly, because the air dries out and the timber gives up moisture. But a door that has swollen and shrunk for several seasons can stay slightly out of shape, and a lock that has been forced in the meantime may be worn. It's better to correct the strike or hinges now than to wait for winter.
Should I plane the door myself?
We'd suggest not, at least until you've checked the hinges and the strike. Quite often a door that binds after rain has really dropped on loose hinge screws, and trimming wood off at the height of summer can leave a gap later. If carpentry is needed, have the bare edge sealed afterwards.
Can I just spray something into the lock?
Only what the lock's maker recommends, and only if the lock is stiff with the door open. Makers differ: some specify graphite, others their own care spray, and silicone-based products can turn tacky. If the lock works freely with the door open, the problem is alignment, and lubricant won't help.
Need a locksmith to look at it?
If this hasn't solved the problem, our lock repairs service covers it. We're a mobile locksmith in Centurion, so we come to your door.
Sources and further reading
- Wikipedia: Centurion, Gauteng (climate) — warm to hot summers (October to April) with late-afternoon showers, thunder and lightning; dry, sunny winters
- Wikipedia: Highveld — Highveld rainy season is in summer, with afternoon thunderstorms typical in November, December and January
- Wikipedia: Climate of South Africa — interior rainfall concentrated in summer, with brief afternoon thunderstorms; winters dry and sunny
- SAnews: SAWS warns of severe thunderstorms in Gauteng, Mpumalanga (20 March 2026) — SA Weather Service warning of severe thunderstorms over northern parts of Gauteng
- Mail & Guardian: It's the season for thunderstorms, says SA Weather Service — SAWS: it's the season for thunderstorms and severe thunderstorms
- WOODweb: The movement of wood — wood shrinks and swells across the grain when its moisture content changes; seldom lengthwise; coatings slow moisture change
- Wikipedia: Wood warping — wood takes up and releases moisture indefinitely; uneven expansion causes warping
- ASSA ABLOY South Africa: Product care and maintenance (PDF) — warped doors and distorted frames load other components; graphite for cylinders; avoid silicone-based lubricants