How to Fix a Sticky Door Lock: What Locksmiths Use
Your front-door key grinds or sticks, and the internet says WD-40 or graphite. Locksmiths use neither most days. Here's what they reach for, and why.
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The key goes in. Then it grinds, or it won't turn until you lift the door and jiggle. Look it up and you land in an argument. One camp says WD-40, the other says graphite, and both sound certain.
If your front-door key has started to grind or stick, there's a third answer. Working locksmiths mostly use neither. They reach for one of two cans, and they've said so in their own threads for eight years.
Why is my door lock sticking?
Before you spray anything, the trade asks a few questions. When a homeowner put this exact problem to r/Locksmith, one reply wanted to know whether the key was "original, or a copy-of-a-copy-of-a-copy". A worn copy will stick in a perfectly good lock, and that's a trip to the key cutter, not the hardware aisle.
Another locksmith said weather swings make a lot of outside locks want "a shot of lube". Then came the check: make sure it isn't "a worn lock or key".
A third asked whether it "works smoothly with the door open". If it does, the lock isn't your problem.
What do locksmiths use?
Two cans come up again and again: Tri-Flow and Houdini. In a "preferred lock lube" thread a locksmith started this year, one answer was "Houdini and tri flow are my daily users". Another keeps both, and a third can, "for different circumstances".
The homeowner's thread, eight years older, got the same two names. "Houdini is all I stock now", said one. "Triflo for sure", said another. A few in that thread use a silicone spray instead, and nobody argued with them.
They're not the same kind of product, and the difference matters when you choose. Tri-Flow is a PTFE lubricant. Its maker says it's "Formulated with P.T.F.E.", carried in a light oil with solvents that "soften and remove dirt and contaminants" on the way in.
Houdini's maker says little about what's inside. The trade magazine Locksmith Ledger reports that the formula has no "grease, graphite, PTFE, or silicone", and that it does contain "low-viscosity synthetic base oils and solvents". That makes it a cleaner that leaves a thin lubricant behind, rather than a PTFE lube.
The reason locksmiths like both comes down to dirt. The most detailed voice in the preferred-lube thread put it this way.
...we use lock lube as a cleaner, not just a lubricant. Houdini and Triflow flush out the dirt.
u/conhao, in r/Locksmith
The same locksmith won't put Kroil in a lock, because it "stays wet" and gathers fine dust into "a sticky mess". That's the test behind most of their picks: does it carry the grit out, and does it stop being wet.
Did anyone test them?
One locksmith did, for three years. Jason Meeks of SE Lock and Key in Jackson, Mississippi, sealed about nineteen lubricants onto lock cylinders and latches. Three years on, with salt and freezing rounds along the way, they all came out of their bags in a video called Lube Off 3.
It's one tester in one dry shop, judging by eye and feel. It's also the only test of its kind we found.
Tri-Flow came out as the clear winner. There was no harm to the metal, the brass was still bright, and the cylinder turned freely.
Houdini did less well. An earlier round of the test had ranked it top. By year three it had moved to the honourable mentions, with some corrosion showing and a rough first turn of the key before it freed up.
The Locksmith Ledger, which covered his tests, still lists Houdini among the products that do "a fine job of flushing existing materials from keyways while leaving a lubricant in one pass".
Tri-Flow or Houdini?
Price first. Locksmiths who buy both say Tri-Flow runs "nearly double" the price per ounce, and one in a thread from last week said Houdini "works just as well". Those are trade prices, so your shelf may differ, but both threads that mention price tell the same story.
Smell comes up in every one of these threads. Houdini smells of citrus, and most who mention it love it: "the magic locksmith cologne", one called it. One locksmith eight years ago found it "more invasive on a residential call" than a plain lubricant.
Tri-Flow has a smell of its own. One locksmith does daily work with it and switches to Houdini inside people's homes, where "the rather pungent smell" of a good dose of Tri-Flow might bother a client.
On cold weather there's one voice. A locksmith says Tri-Flow "works better in really cold temps" than Houdini, and nobody else weighed in. Tri-Flow's maker rates it for extreme cold and heat; we couldn't find a published range for Houdini.
Tri-Flow can be harder to find on a shelf. As of late September 2026, a locksmith in r/Locksmith couldn't buy it locally any more. So the question went to the trade: where does everyone else get it?
The answers: Ace Hardware, Grainger, Amazon, and "most bike shops". The same locksmith prefers the small aerosol can, because the large ones have died halfway through more than once.
A locksmith near Death Valley summed up the whole argument.
I carry both. Neither is better, just better for "this".
u/ILockStuff108, in r/Locksmith
How do you put it in?
If somebody has already put graphite in the lock, get it out first. The Ledger's writer learned this the hard way. Their advice is to "flush existing graphite" out with contact cleaner. Only then does another lubricant go in.
A short burst into the keyway is enough, and not much of it. One locksmith's only complaint about Houdini is that it's so good they end up using "way, way too much of it".
Run the key in and out a few times, and wipe it on a rag between goes. Expect the key to come out grubby the first couple of times. That's the dirt the locksmiths were talking about.
Is WD-40 good for door locks?
Ask r/Locksmith and the loud answer is no. A renter's handyman had sprayed WD-40 into every lock in the house. One locksmith's answer was that it "should never touch locks", because it leaves an oily film that catches debris.
A milder voice in the same thread said it "doesn't stick around", so it isn't much of a lubricant.
The dissent sits in the same thread. One commenter had watched a boss use WD-40 in locks for ten years with no problems, called the locksmiths' reaction "histrionic hyperbole", and pointed at the Lube Off test. That's a fair point.
In that test the WD-40 lock was a little sluggish and a little sticky after three years, but it still worked. The tester's closing word was that anybody can use it in their lock and be fine.
The Ledger splits the difference. WD-40 is a penetrating oil, "not a lubricant", and it "makes things work great for a few days - very few". WD-40 won't ruin your lock, and it won't fix a sticking one for long.
Graphite is the older answer, and the trade is harder on it. "DO NOT USE GRAPHITE", one locksmith wrote, in capitals. When the renter asked why not, another explained that it stains rugs and clothing and combines with moisture and lint into "a crusty grit".
The Ledger gives it a narrow place: interior locks or dry conditions, used "very sparingly", one puff.
A locksmith of forty years on the Garage Journal forum would still choose powdered graphite for a clean lock that's "a bit stiff", and Tri-Flow for one that's gummy. A sticking lock on an outside door is rarely the clean, dry case.
Start with the key. A copy of a copy needs replacing with one cut from the original, before you buy anything.
Then get a can of Tri-Flow: the lube that came out of the three-year test clean, and the one a locksmith grabs for a gummy lock. Houdini is the cheaper can plenty of them use every day, and the one to pick when the smell or the shelf decides it.