A urinal does not block overnight. Urine scale grows by a few tenths of a millimetre a month and narrows the outlet throat for months before the water stops draining altogether. The blockage is the last step in a process that has been visible the whole time — through slower drainage and an odour that comes back an hour after cleaning.
How the deposit forms
Fresh urine is slightly acidic, and the calcium, magnesium and phosphates in it are dissolved. Bacterial urease breaks urea down into ammonia and carbon dioxide, the pH rises above 8, and the dissolved salts start to precipitate out as struvite and calcium phosphate crystals. The crystals take hold on microscopic imperfections in the glaze and on the rubber seal below the throat.
Hard water speeds the process up, because it brings extra calcium into the system. In the parts of Croatia with hard water the deposit grows noticeably faster than in areas with soft water.
| Period | Condition of the throat | What you notice |
|---|---|---|
| 0–2 months | Thin film on the walls | Nothing |
| 2–6 months | Layer up to 1 mm | The odour returns quickly after cleaning |
| 6–12 months | Cross-section narrowed by up to a third | Water drains visibly more slowly |
| 12–24 months | Cross-section narrowed by up to two thirds | Standing water, constant odour |
| after that | Complete blockage | Urinal out of service |
What it costs if you let it run
The cost is not just the plumber's call-out. In a hotel or a restaurant, a washroom out of use also means a guest who notices. In a production plant working to HACCP, a blocked drain in the washroom ends up in the inspection report.
Mechanically cleaning the throat and the trap deals with the deposit that is already there, but if nothing else changes the same process starts again the very next day.
Prevention instead of remedial work
The most reliable way to stop the deposit forming at all is to break uric acid and proteins down before they have a chance to precipitate. That is what bio-enzymatic tablets do: with every flush, bacterial cultures are released into the throat and break down the organic load while it is still in solution.
The order of work for a urinal that already has a problem:
- Remove the existing deposit mechanically — a tablet will not dissolve it
- Fit a cage with a tablet in the throat
- Stop using acid and chlorine products, because they destroy the cultures
- Replace the tablet every 30 to 45 days
For buildings with several urinals the bulk pack works out better: a 5 kg tub holding roughly 65 tablets, used to refill the cages you already have — about three times cheaper per tablet than the pack that comes with a cage.
When scale is not the only problem
If a urinal drains slowly but the throat is clean, the blockage is further down the stack and needs a plumber. If there is an odour but drainage is normal, the cause is most likely a dried-out trap — there is more on that in the article on urinal odour.