Unexplained Damp

[Mr Sparkle]

Can anyone explain this phenomenon?

1. Solid wall (external). Paint stripped in order to decorate at later date

2. Left a mattress leaning on the wall for about a week

3. After disposing of the mattress, the wall had a damp imprint (marked in blue) where the mattress was in direct contact with the wall

4. Used heat and a dehumidifier to thoroughly 'dry out' the wall. Damp mark disappeared.

5. One day later, the damp mark came back

Can anyone explain why this is happening?

 

[foxhole]

You only dried the surface, damp is in the wall not just at surface.

 

[grantmac]

Could be the wall absorbing moisture from something like a plumbing issue or ground moisture. Even if you dry the surface, the actual issue might be deeper in the wall. Make sure to check for any leaks or external moisture sources. Sometimes it helps to use a stronger dehumidifier and monitor it for changes.

 

[ree]

OP,
Why not post a pic of the outside of the wall?
The Hit&Miss vent looks like its closed - is there any other ventilation in the bedroom(?)?

 

[Mr Sparkle]

Could be the wall absorbing moisture from something like a plumbing issue or ground moisture. Even if you dry the surface, the actual issue might be deeper in the wall. Make sure to check for any leaks or external moisture sources. Sometimes it helps to use a stronger dehumidifier and monitor it for changes.

Thanks. Def not plumbing or ground moisture.

The damp imprint is in the exact place the mattress was in contact with the wall.

OP,
Why not post a pic of the outside of the wall?
The Hit&Miss vent looks like its closed - is there any other ventilation in the bedroom(?)?

Vent is closed and never opened as room becomes an ice box. Room has windows

Will upload a pic later. Thanks

You only dried the surface, damp is in the wall not just at surface.

Thanks