Ceiling drip on humid afternoons: gap in the drain pipe

The unit dripped only on humid afternoons. Part of the drain had already been replaced, but the leak came back. The source sat at a hidden joint further upstream, behind a ceiling panel.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Daikin Ceiling10 years oldOfficeMarina South, Singapore

Concern: A drain replacement had already been paid for without fixing the leak, and the worry was that the whole run now needed redoing.
Found: A cold joint at a concealed drain pipe joint behind the ceiling panel: insufficient cement or cure time left a hairline gap that only leaked once enough condensate volume passed through it
Key check: Traced the drain run behind the ceiling panel joint by joint and found a hairline gap at a joint that never fully bonded during installation. Did not rely on replacing the visible drain section alone
Result: The intermittent drip stopped. The unit has since run through several humid days with no return, and no ceiling work beyond the one access panel. The result was a single joint repaired, with the rest of the drain run left intact.

What we were told

Drips appeared near the unit, but only on humid days. Part of the drain pipe had been replaced a few weeks earlier, yet the drip returned. Humid afternoons still brought water down onto the tile, exactly as before.

What we checked

When a drip returns after a partial drain replacement, the source is almost always elsewhere on the run, upstream of the part already fixed. We traced the full path from the unit outward, including the concealed section behind the ceiling panel, which had stayed shut through the earlier work. Dripping only on humid days was the clue: the gap was small enough that normal drainage passed it, but heavy humid-day flow did not.

The replaced drain section was intact and sealed. The earlier work was done correctly; the fault was simply not there.
Staining on the ceiling tile pointed to a drip origin further upstream from the replaced section.
With the ceiling panel opened, one concealed joint was found separated by about two millimetres, never fully bonded at installation.
Pouring measured water through the drain reproduced the leak at that joint at humid-day flow rates, confirming the source.

What we found

The concealed joint had never fully bonded. A drain joint needs enough cement and cure time to weld solid; this one was under-cemented, or closed up before it had set, leaving a hairline gap. Ordinary drain flow passed the gap without issue. On humid days the unit pulled far more moisture from the air, so the drain ran fuller and backed up at the gap, dripping onto the ceiling tile. The leak sat upstream, behind the panel, not in the section already replaced.

What fixed it

We cleaned both faces of the joint, applied a proper amount of fresh cement, reassembled it, and held it firmly while it cured for the recommended time. With the panel still open, we checked every other concealed joint on the run, and all were sound. We then ran the unit at full cooling and maximum fan to force peak drain flow. The ceiling tile stayed dry, and no other section needed replacing.

Outcome

The intermittent drip stopped. The unit has since run through several humid days with no return, and no ceiling work beyond the one access panel. The result was a single joint repaired, with the rest of the drain run left intact.

What this case teaches us

A leak that returns after a repair is usually somewhere else

When a drip returns after part of the drain was replaced, the new section is rarely the fault. The source is usually further along the run, often in a concealed stretch the first repair never opened.
A leak that shows only on humid days often traces to a joint that never fully bonded. Too little cement or cure time leaves a gap that ordinary flow passes but heavy condensate does not.
Send a photo of where the water appears and note when it happens, before anyone quotes a full drain replacement.

Questions this case answers

The ceiling drip came back after part of the drain was replaced. What now?

Look upstream of whatever was already opened. At this Marina South office the replaced length was intact and sealed, while staining on the ceiling tile pointed further back along the run. Behind a ceiling panel sat a joint separated by roughly two millimetres that had never fully bonded at installation. That was the source.

Why would a drain leak only on humid afternoons?

Because the gap passed ordinary flow but not a heavy one. On humid days the unit pulls far more moisture from the air, the drain runs fuller, and water backs up at the weak point. Pouring measured water through at humid-day rates reproduced the drip at that exact joint and confirmed it.

What makes a drain joint fail years after installation?

Too little cement, or closing the joint before it had cured. Either leaves a hairline gap instead of a solid weld. It can sit unnoticed for years because normal drainage passes straight through without trouble. Only peak condensate volume exposes it, which is why the leak reads as random rather than constant.

Does a returning leak mean the whole drain run needs replacing?

Rarely. With the panel open, every other concealed joint on this run was checked and all were sound. One joint was cleaned, re-cemented and held firmly while it cured, then the unit was run at full cooling and maximum fan to force peak flow. The ceiling tile stayed dry. One repair, not a full run.

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