UKH

I was reaching into the back of the gear cupboard this morning to pull out the warm stuff, mostly to wear while working at my desk, when I noticed black mould across the inner wall.

Any super tips for getting rid of the dreaded stuff? I hear repainting over it doesn't really work and ventilation is the key - hard to do with a cupboard. 

I've washed it down with bleach/water solution and will attack it properly with a scrubbing brush over the weekend. The wall in question goes directly to the outside and is on the second floor. The cupboard has always been a bit damp so nearly all the gear is in storage boxes anyway, which luckily means that is okay. 

We own the house, well the bank do, so there is not a landlord responsible. 

Might be worth adding some insulation on the inside of the wall so the warm, moist air inside isn't reaching the cold outside wall and condensing.  Boxing in the back of the cupboard may even suffice.

You can ventilate a bit by adding a grille or two to the door.

Ventilation and moisture control are the key things. Extractor fans, don't dry clothes in the house, open windows when you can, keep your trickle vents open etc. Make sure exterior is water tight and guttering is in order. Insulation potentially helps as it tends to form on cold walls where condensation forms. It becomes an arms race though as you'll always end up with a 'colder' wall somewhere and insulation may be impractical or expensive. Attacking it with bleach as soon as it starts. Cupboards are the worst along with areas where you have furniture against walls so it doesn't get air flow so be vigilant.

Yep - this.

There are essentially 3 potential causes:

1) Rising damp - up through the floor

2) Water ingress - leaky gutters, roof, windows, water pipes etc

3) Lifestyle - lack of ventilation, drying washing indoors, hot baths and showers, heating turned off in winter causing condensation

I'd wash it down with mould and mildew remover and paint with anti-mould paint. Consider which of the 3 is causing it (more ventilation is rarely a bad thing!) and make any changes you might need. Then wait 3 months and see if it comes back...

I had a cupboard against an outer wall which had this problem. There was nothing to be done except regular applications of mildew remover available from my local supermarket: Astonish - UK's No 1 Mould and Mildew Blaster. Apple Burst, Vegan and Cruelty Free. Bright green bottle.

It worked; try to catch the mould early.

I had a similar problem so painted the walls with black paint and it seemed to disappear. 

Ha! Excellent 

Thank you very much all. I'll attack it with more anti mold stuff and see what the options are in terms of insulation. Appreciate the excellent suggestions. 

My former lodger (no, I didn't chuck him out! ) managed to create some - the only mould I've noticed anywhere in the house bar a bit on the silicone in the shower cubicle - by his pillow being up against the wall!

Doesn't take much.

Good advice upthread but here's another spanner in the works: How old is your house?

If your house is of traditional construction (ie. generally built before 1920 with solid masonry walls) then it would have been built to be breathable. No damp proof course, no cavity wall, and porous building materials such as lime mortar. The effect of this is that whilst the buildings aren't as thermally efficient as modern houses, they do a lot better at buffering moisture levels and often feel more comfortable than modern buildings as a result.

The caveat though is that most houses (especially the unlisted ones) have been badly treated over the last few decades, being repointed or rendered in cement and replastered indoors with gypsum and painted with waterproof paints. All of these are bad, but the latter point could be crucial in your case as if you've used a waterproof paint and/or plaster you'll get condensation and mould on your walls instead of them absorbing the excess moisture.

If the above describes your situation, I'd recommend repainting and/or replastering the wall with something porous. If not, just do what the others above have said.

Nb. on Insulation. As others have pointed out, a bit of insulation on the wall will make it less cold and it will attract less condensation, but the problem will likely shift to other uninsulated areas. If you're going to retrofit a house with insulation it ideally needs to be a whole-house job, designed to minimise cold spots and reduce the risk of upsetting the building's hygroscopic performance. If you insulate an old house without taking this into account, you are risking damaging the building and your own health.

If it's in a corner, then wet some kitchen towel in bleach, roll it up into a "cigar", and place against the black stuff. Come back the next day.

 If the problem is due to internal moisture I imagine one could just insulate the outer wall for one room rather than the whole building as each room behaves essentially as a separate entity. Unintentionally I did this by building a lean-to outside our backroom. This has made the backroom noticeably warmer probably partly because the prevailing wind (and rain) no longer hits the back wall and being draughty the lean-to does not allow a buildup of moisture laden air.

Agree with the other answers about ventilation, treatment and checking where the dampness comes from - though I favour condensation.

Another thing to consider, if funds and space in the room is available, is having the outside walls of the room  insulated with something like 100mm of Kingspan. You need to know what you are doing, or get someone who does but it does make a difference.

Dave

Could you change the cupboard door for a louvered one?

Also leave a bit of a gap between your stuff and the wall to allow airflow.  

Sort of... but what you did and insulation are very different. I doubt the u-value of your wall has changed, it's just drier and more sheltered now. A similar effect could be achieved with render.

If you're dealing with traditional buildings care needs to be taken not to damage the fabric of the building. If you were to take up Tringa's suggestion on my house for example, by sticking kingspan on its outer walls, you would be creating an impermeable barrier for moisture. Moisture tends to move outwards in traditional buildings both through vapour diffusion and capillary action until it meets an outside surface and evaporates. If you block its path moisture builds up in the wall and eventually you end up with serious problems. 

Edit: I realise Tringa is talking about insulating the inside of the exterior walls, in which case see my earlier comment. Another potential downside to internal insulation is overheating in summer. The mass of your walls buffers the heat in summer, a benefit that is lost if you use internal insulation.

I didn't mean to imply I'd added insulation. In my case the original external wall  with old render could presumably have got damp, mainly by being exposed to driven rain (no black mould though) and evaporation would have been slow especially when cold. Building a lean-to allowed it to dry out (old external wall now internal) and less heat would have been used up evaporating water from the wall or by so much heat being removed by prevailing winds. Certainly no barrier to water movement. It certainly did make the room warmer, though admittedly a certain amount was due to the lean-to reducing draughts. Downside is the backroom is now a bit darker even with most of the lean-to roof and walls being transparent.

I am a total non-expert but I agree with you, FWIW

[1] In a previous flat years ago we had bad black mould on several walls. Scrubbing it off, plus constant ventilation from windows always left open a crack, got rid of the black mould permanently

[2] Recently we helped our friend who doesn't speak English get a new boiler installed in her (older) house. The boiler installers sent an HVAC expert who took a long time over 2 visits inspecting the whole house. He noticed that none of the windows in the house had those little vents at the top (I don't know what the heck they're called). He left a written report saying that installing them was an absolute must (our friend the owner ignored this advice). PS this is not my advice, this is what the HVAC guy said

Thank you for your response. It's much appreciated. Most of the house is pre 1900s, however this particular room is part of an extension added on in the 80s.

Another vote for Astonish Mould and Mildew remover. I spent ages unsucessfully with bleach on a canvas garden umbrella trying to get rid of black mould. One spray of Astonish and it all vanished! 

I tried using the Astonish stuff to tackle ingrained black mould on the sealant round the shower tray. No effect at all. What worked great was the suggestion by Michael Hood upthread, using rolls of tissue and neat bleach.

Screwfix do a really good mould remover, lasts ages and is good price

They're called trickle vents. They're now compulsory but that wasn't the case for replacement windows until this year.

Thank you for the information! That's good to know

Very few houses have them other than social housing because their requirement is so new.  Indeed their presence used to be the easy way to identify who owned their house and who didn't in an area of mixed tenure!

Most even vaguely recent uPVC windows can be locked slightly open to get the same effect, though.

Top tip for today!

The sun is out so lift the net curtains and blinds to let sunlight into the house. It dries condensation, makes an appreciable difference to the temperature and cuts the energy bill a bit.

Thanks Lankyman, appreciated