What are these black marks appearing on walls?

[Borgster]

Hi all

Looking for some help to explain what these strange marks that are appearing on the walls of some of the rooms of my father’s house. The house is a double brick home and these started appearing about 12m ago. They are not on the surface but appear to be coming through the paint from the wall itself. They can’t be cleaned off. Any help would be appreciated. The house hasn’t been painted in many years so it’s not a result of poor prep work on a recent paint job

[JacobZ]

Hi @Borgster,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

It's tough to tell from the photo but I suspect they are water marks from moisture coming through the wall. This would be a bit strange considering double brick homes have an air gap that should prevent condensation from occurring on the inner brick wall. 

Can you advise if the walls in question are external walls, or internal walls that simply separate rooms? Do the spots feel moist at all?

I can't be certain, but there may be moisture getting into the air gap between the bricks and seeping through the brick behind the render. This would likely mean there is a water entry point somewhere above. 

If this is the case, you may need to contact a builder to assess the issue.

Allow me to tag some of our helpful members to see if they have any ideas on what this could be, @Dave-1, @Nailbag, @DIYGnome.

Let me know if you have any further questions.

Jacob

[Dave-1]

Evening @Borgster 

My first thought was water lines coming through the plaster. Do you know if the house has been flooded before? You could get a moisture meter to check yourself but maybe a builder as @JacobZ has suggested to assess the wall. 

Is it all the rooms on the same level of the house and do the lines match up height wise on the plaster?

Dave

[Nailbag]

Hi @Borgster I'm assuming these are all internal walls but to have some form of water damage in various rooms around the house, would mean there is a very substantial water penetration that would not be restricted to just the walls, but to the floors. Are these walls rendered or plasterboard directly fixed to the brickwork? If plasterboard then. the effected areas would be very soft to press inwards with your fingers, indicating some form or water ingress. Long term effects water/moisture ingress would result in signs of mould on walls and floors. But you haven't mentioned this. 

This is a toughie to advise remotely so, I think it would be worth contacting local flood damage companies to inspect the property even though this isn't a floor related issue. They have the expertise to establish anything serious or rule it out. In which case it might be as suggested poor preparation in recent paint work?

Regards, Nailbag