Mould/damp on internal wall - what can I do?

[honeycrumpet]

I've got an alcove in my living room that has a cupboard and shelves built in (built by the previous owner). The cupboard is at the bottom and then there are shelves above. I was keeping books on the shelf which is also the "roof" of the cupboard IYSWIM, and I've just taken them off to sort for the charity shop and discovered some really horrific mould - see attached! First 2 pics are the shelf/top of cupboard and the third is the inside of the cupboard. They both have a wooden board at the back which is covering the brick/plaster wall and I think there must be damp in that wall which has now spread out onto the the shelf and cupboard.

So - how can I clean it first of all? Mould spray? And can I stop it coming back or do I need to get a professional in?! We're hoping to put the house on the market soon and I'm worried that this might be a problem on a survey if we can't fix it.

It's an internal wall - the shared wall between mine and my neighbour's house - so I'm not sure if that makes it better or worse from a damp treatment point of view?

Any ideas welcomed!!

Do you know what room is on the other side? Could be some sort of leak if there is pipework in the wall

I think my neighbour's house is a mirror image of ours so it's his living room too. We have a back boiler in the fireplace which is right next to the alcove so it could be water pipes from that - I didn't think of that, thank you!

First thing I would do is remove the back of the cupboard and the shelves to see what’s going on. No point in cleaning till you find and cure the source

Agree that the source needs to be resolved. Once you've done that, you can clean with diluted bleach to kill the spores. We have condensation based mould on our external walls, but I painted with Wickes own brand Anti mould paint, and that has seemed to deal with the problem for us.

That's pretty bad damp.

Could be the pipes in the boiler as PP suggested.

The cynic in me, would think this has been a problem for long time, and the previous owns built the cupboard with sides and back to disguise the issue when selling.

Be prepared it could be quite bad behind the boards.

Thank you, I think we will have to investigate and take the boards out. DP is of the opinion that we just clean it and sell it and then it's someone else's problem (he wants to do as little as possible and spend as little as possible and save our money for the next house), but I agree that that's probably what the previous owner thought too and it's probably a more serious problem. I just worry that it will be an obstacle to selling if we get a buyer who's savvier than we were.

That looks like a longstanding leak to me too, especially as your boiler is close by. Do you have your boiler serviced regularly, and is it running okay? I can see where you are coming from regarding hiding it, but if I discovered something like this I would want to get to the bottom of it. My worry would be that it might suddenly get worse, which would then need even more fixing up and repairing. And, with a boiler, you can bet it would be at the most inconvenient time (Christmas, beast from the east etc). Of course, it may not be the boiler, but it needs investigating.

Yeah @longearedbat I reckon it is time to have the boiler serviced - it's running fine but that doesn't mean it isn't the source of the problem, so worth having a look (now just to convince DP it's worth it! )

Thanks all - you've helped me draw up a to-do list! Case closed I think.

You won’t be able to hide that from a buyer because the moisture readings in the wall will be crazy. A surveyor will pick it up straight away and then you risk losing a sale. And, umm, it’s morally wrong?

When we had damp in a similar area it was to do with the chimney stack. It wasn’t expensive to fix but quite messy as the plaster needed knocking off.