Urinal odour almost never comes from the ceramic the cleaner has just wiped down; it comes from the outlet throat underneath it. That is where urine scale builds up, and the bacteria living in it break down urea and release ammonia. This is why a washroom still reeks ten minutes after cleaning — what gets cleaned is what you can see, while the source sits two centimetres deeper.
The second source is the same as with floor drains: a dried-out trap. In a urinal that goes unused for weeks — over the holidays, out of season, or in a closed part of a building — the water evaporates and sewer gases enter freely.
What urine scale is and why you cannot see it
Urine is almost sterile and slightly acidic as it leaves the body. The moment it meets air and bacteria, bacterial urease breaks urea down into ammonia and carbon dioxide. The pH rises, and with it the dissolved calcium, magnesium and phosphates start to precipitate out as crystals. That deposit — struvite and calcium phosphate — clings to the walls of the outlet throat and the trap.
The layer grows by a few tenths of a millimetre a month. For the first month you see nothing. After six months the cross-section of the throat can be a third narrower, and the odour is constant.
The key point: scale is not dirt. It is not removed by cleaning the surface, because it is not on the surface.
Why the usual products make the problem worse
Acid products (hydrochloric, phosphoric, sulphamic acid) dissolve part of the scale. At the same time they attack rubber seals, and with repeated use they damage the ceramic glaze as well. On a rougher glaze the scale then builds up faster next time, so the interval between cleans keeps getting shorter.
Chlorine products kill bacteria, including the ones that would break uric acid down before it precipitates. After chlorine there is nothing left in the drain to break down the organic load, so the deposit builds again from scratch, and faster.
Scented blocks and balls mask ammonia but do not remove it. Staff replace them weekly, the cost adds up, and the cause remains.
| Approach | Acts on | Result after 6 months |
|---|---|---|
| Acid product | Surface scale, as far as the product reaches | Damaged glaze, faster build-up |
| Chlorine product | Bacteria, useful and harmful alike | No breakdown of uric acid |
| Scented ball | Nothing — it covers the odour | Scale grows unhindered |
| Mechanical cleaning of the throat | Deposit that has already formed | Helps, but needs a plumber |
| Bio-enzymatic tablet | Uric acid before it precipitates | The throat stays clear, with no odour |
How a bio-enzymatic tablet works
GD Uri-Tabs™ is a pressed tablet containing more than three billion active bacterial cultures. It sits in a vented cage in the throat of the urinal. With every flush it releases some of those cultures, which break down uric acid and proteins before they have a chance to settle out as scale.
No acid, no chlorine, and no fragrance covering another smell. The formulation is fully biodegradable and compatible with septic systems.
- One tablet lasts 30 to 45 days, depending on traffic
- The cage holds the tablet in the right position and stops it floating off into the drain
- It also works in waterless urinals, where scale is the biggest problem
- It does not damage ceramic, seals or pipes
If it smells even when the throat is clean
Then the cause is the trap. A urinal that is not used — over a holiday break in an office, over the summer in a school, out of season in a hotel — loses its water barrier within two to four weeks. The solution is the same as for a floor drain: a passive silicone seal that closes the drain mechanically, without water.
In practice the two problems often appear together. The tablet keeps scale and ammonia under control, while the seal stops sewer gases when the trap dries out.
A short guide for the facility manager
- The odour returns within an hour of cleaning → scale in the throat, not the surface
- Odour after a break of several days that disappears once the urinal is used again → a dried-out trap
- Slow draining → scale has already narrowed the throat; mechanical cleaning first, then prevention
- Odour in only one urinal out of six → check the venting on that stack