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Community and Q&A

Has anyone else experienced mold problems from lining interior walls with corrugated tin?

bsueharper0112 | Posted in Interior Design on

The place I was renting last had a room where the walls and ceiling were lined with corrugated tin on the inside. There was also a combination AC/Heater window unit in that room. My landlord is in total denial that his remodel job caused a very serious mold infestation. I moved out after having many ongoing symptoms of toxic mold exposure and immediately I started regaining my health. I live in southwest New Mexico in a town that boasts of its hot springs where water is just below the surface of the ground. Just wondered if anyone has experienced what I have.

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  1. GBA Editor
    Martin Holladay | | #1

    My guess is that these panels weren't made of tin. They were probably made of galvanized steel.

    Metal roofing panels are a vapor barrier. During the summer, if these panels are installed as interior finish materials in an air conditioned home, the back side of the panels (facing the exterior) can be cold enough to become condensing surfaces for moisture in the wall assembly. (Inward solar vapor drive often drives exterior moisture through wall assemblies toward the interior.)

    If that's what happened at the house you lived in, mold could have started growing behind the steel panels.

  2. Expert Member
    Dana Dorsett | | #2

    Although, in most of NM the summertime outdoor dew points are WELL below what any air-conditioned interior would hit. There may be very site-specific issues related to the hot springs, or it could be something else.

    Typical mid-summer peak dew points in say, Deming,NM are in the ~65F range, and the midsummer averages are ~55F. Normal humans are cooling their houses to that level. The AC condensation explanation might make sense in the humid southeast (with outdoor dew points in the 70s ) but not the dry southwest.

    Without a complete description of the wall's layer stackup from the exterior paint to the sheet metal interior it's hard to get a handle on the other possibilities.

    In general, if the room is air conditioned and has a more vapor-permeable interior finish, the air conditioning would dry out the wall. If the house has low vapor permeance on both the interior & exterior it could create a mold-farm pretty easily from groundwater wicking, if the water table is just below grade and there is no capillary break between foundations & footings and the walls/floors.

  3. iLikeDirt | | #3

    New Mexico experiences late summer and early fall monsoons that can see the outdoor relative humidity rise so high that the dew point can easily get into the 70s. This will usually be during a heavy rain, followed up by bright sun, so the inward solar vapor drive theory makes some sense given the incidence of moisture reservoir cladding around here (mostly stucco). If the wall structure is wood and the stucco has been painted with latex paint (common), there's your low-vapor-permeance-on-both-sides-mold-farm, especially if the building has a flat roof, as the wall-roof intersection and unprotected windows are places where a lot of water can enter the stucco.

  4. Expert Member
    Dana Dorsett | | #4

    Those very high dew monsoon points are very short lived. Even on days when the dew points reach the 80s (rare, but it happens), the daily average dew point is under 70F.

    The US southwestern monsoon season is usually the first half of July, The highest dew point measured in Deming NM this summer was 69F, at about 10PM, and it dropped to 47F by 6PM the next day. The average outdoor dew point for the first half of July was 58-60F. This year late-August/September was unusually humid, for the region, but the August/September peaks were in the mid-60s. The total August/September rainfall was only about 1/3 the amount that fell in the first half of July.!dashboard;a=USA/NM/Deming
    Even with sun-driven vapor drives and condensation events on the sheet metal, this is unlike generate enough moisture accumulation to cause a problem on an unvented latex painted stucco assembly, but it might with a more vapor-tight alkyd painted assembly.

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