I've noticed that whenever someone takes a hot shower in my bathroom, a specific crack in the tiles of my wall shows a pattern in the condensation, more specifically, a region of about 1cm around the crack doesn't form condensation.

This crack is exactly above the toilet's pipes, so I've thought that because of the water running inside the pipes, the air around it would have a lower temperature, and because of the crack, it would escape and cooled the region, but I'm not sure about this, because the vapor is hot, so a cooler region would condense more. Maybe the air inside the wall is drier, so it would prevent condensation?

bathroom tiled wall

crack closeup


This night was rainy and cold, and this time the gap was visibly narrower than yesterday.

narrow gap

  • $\begingroup$ Shouldn't the water running in the pipes be hot? So that you actually get hot air that can condense? $\endgroup$ Mar 6 at 16:52
  • $\begingroup$ Here in Brazil, we use a different system, we use electric showers, so the water runs cold til is warmed in the shower's head, but as I've said, these pipes are the toilet's pipes, so anyways they would be cold water pipes $\endgroup$
    – As Aves
    Mar 6 at 16:59

That crack was probably repaired with silicone caulk sometime in the past. As it cures, silicone caulk tends to leave an exceedingly thin layer of silicone in the immediate vicinity of the application, which covers up all the tiny nucleation sites at which water vapor would otherwise condense.

This effect is amazingly persistent. I used silicone caulk to seal the outside window frames to the glass they held which I first moved in that house, and 20 years later water droplets and condensation were still avoiding the strip of glass 3/4" of an inch wide, right next to the caulk zone.

  • $\begingroup$ Very interesting. Could this thin layer caulk be effective against mold growth on cold walls? $\endgroup$ Mar 6 at 19:16
  • $\begingroup$ Nice try, but I live in this house for ~10 years, and this crack appeared ~5 years ago. We, unfortunately, did not seal this crack, so I don't think that's the cause. But even if I missed someone sealing it, the region of the crack doesn't have any residue of sealant. I've edited the question and added a closeup pic of the crack $\endgroup$
    – As Aves
    Mar 6 at 19:31

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