Garage wall stain

[Denray]

What causes the white color on the interior of this garage wall? It's redwood. The exterior siding is wood also.

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[Jerry Simon]

Looks like fungus

[Tom Raymond]

Salts. It's essentially the same as efflorescence, the siding gets wet when it rains, the paint prevents it from drying to the exterior, so it dries in and leaves behind anything dissolved in the water.

[John Kogel]

What causes it? Moisture. []

[Denray]

Yep, the outside was painted. Thanks for the info all.