We have a bathroom in a detached structure from our house. We purchased it and have not used this for 6 months.

I just noticed this powder on the walls and I touched some of it on the wall and it just crumbled like baby powder.

It is also on an adjacent wall. There's also white stuff around a hole in the ceiling.

It is also under the sink...around the pipe.

Note this powdery material has build up on the wall so that it is 1/2" or so thick.

I don't know what all of this stuff is and whether it's the same substance in other places in this bathroom.

wall with white powder wall ceiling - not directly above wall under sink opposite wall

2 Answers 2


Efflorescence! Efflorescence is a crystaline deposit of water-soluble salts on surfaces of masonry, stucco or concrete. Water brings these salts to/toward the surface and then the water evaporates leaving behind the crystaline deposit.

Note: If one has efflorescence on the surface, one can count on having similar deposits just below the surface, too. These sub-surface deposits tend to cause crumbling of the masonry, stucco, or concrete structure.

The presence of mineral deposits on water pipes indicates one of three things:

1) there's a pin-hole in the pipe through which water is penetrating and evaporating to leave behind calcium (and other minerals) behind,

2) water is leaking from a fitting and leaving behind deposits, at the lowest point of moisture travel, before dripping or evaporating,

3) water is carrying minerals from an adjacent wall, ceiling, etc.; which runs down the pipe and leaves behind deposits, from the lowest point of moisture travel, before dripping or evaporating

  • Can efflorescence build up beyond on the surface such that it grows away from the wall? There was probably 1/2" or so of it build up!
    – milesmeow
    Jan 8, 2017 at 17:59
  • 1
    Your asking ^ if water, carrying minerals in suspension, can flow over previously deposited minerals; even if those deposits are on a vertical surface and, thereby, increase the extent by which those deposits protrude from the vertical surface. The answer is, "yes". Jan 8, 2017 at 18:13

There are a number of reasons this can happen. One that I see a lot is an area that gets water but dries out (hence no mold). The drywall will start breaking down and flaking. Along with mold this is a great reason you start off with an oil based primer in bathrooms.

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