Narrow black lines on interior walls

[GillObrien]

Hi all

I have noticed a series of narrow black lines on an interior wall between the bathroom and the bedroom. They are about 30cm long and 1cm apart and only appear in an area about 30cm by 30cm. This area is behind the tap end of the bath but about 50cm above the bath level. There are none at the level of the bath. I put photos of the lines and the corner they are in (just above the drawers on the wall with the door).

We don't use the bath regularly and only shower whilst sitting in it, so that wall does not get directly wet. It is tiled with some 1970's tiles (I attach photos for your viewing pleasure!). It does get condensation although we always open the window after using the bathroom until it has cleared. It is probably about 17 degrees in the bedroom and bathroom.

I read about ghosting but the lines there seem far apart. I am not sure what the walls are made of. Downstairs it is a type of 5-6cm thick board with an insulated middle.

Is this likely coming from humidity in the bathroom? I will redo the silicone around the bath anyway in case there is a small leak as I note it is black behind the taps. Should I seal the grout on the wall as well?

Many thanks,
Gill

 

[JohnD]

Are they vertical or horizontal?

How old is the house?

I think it is damp from a leak round the tap.

Take off the bath panel, look for damp, and the route of the pipes. They may be inside the wall.

 

[GillObrien]

They are vertical and parallel. The house is from 1978.

There are no pipes in the wall - all the pipes are under the bath and run downwards. I attach a picture. It is all dry underneath.

 

[JohnD]

I don't recognise it then. To highlight damp, tape a piece of clear plastic such as cling film tightly to the wall. If mist or droplets appear under the plastic, the wall is damp. If they appear on the room side, the room is too humid, for example from wet washing.

The plumbing looks OK. What is above that room?

Does the wall appear to be made of plasterboard, of blockwork?

 

[JohnD]

P.s.

The marks might be old dust or smoke marks after something was standing or hanging against the wall, or from a heater. Try rubbing it with a dry clean white cloth.

If you use a sponge damp with detergent, it will get more dust off, but may leave a prominent smudge. Dust marks are very fine and difficult to remove.

 

[RandomGrinch]

Sorry, silly question, but have you tried to wipe the marks off the wall?

Probably completely wrong, but I have seen similar marks on a wall, caused by dust from an ancient bar fire - could they be showing through a recent coat of paint?

Aah, beaten to it!

 

[GillObrien]

I don't recognise it then. To highlight damp, tape a piece of clear plastic such as cling film tightly to the wall. If mist or droplets appear under the plastic, the wall is damp. If they appear on the room side, the room is too humid, for example from wet washing.

The plumbing looks OK. What is above that room?

Does the wall appear to be made of plasterboard, of blockwork?

It is in the loft so above is the roof. But there is no leak as far as I can tell.

The wall is plasterboard.

I will try the clear plastic before I clean it off.

It could feasibility be from an old fire but I doubt it because that would mean that I had not noticed it for two years since we moved in.

 

[GillObrien]

Sorry, silly question, but have you tried to wipe the marks off the wall?

Probably completely wrong, but I have seen similar marks on a wall, caused by dust from an ancient bar fire - could they be showing through a recent coat of paint?

Aah, beaten to it!

I haven't tried to wipe it off yet but I am pretty sure it only appeared recently and the paint was done years ago.

I will try and clean it off now though and see.

 

[GillObrien]

I put a plastic film over one part and cleaned off another. It comes off easily.

I will wait to see what happens with the plastic. Otherwise it must have been there for two years without noticing!