To not know how to get rid of the mould

If it is condensation it will head to the coldest spot, behind a wardrobe or up in the corner of a ceiling etc but you can warm this area up by decorating the cold wall with polystyrene roll, the condensation will then head for the next coldest place like the window, then it's easy to get rid of with a window vac.

HG mould spray and better ventilation. We got new windows and they caused mould because the seals were actually sealed! Then got a new bathroom and extractor fan so it stopped getting worse.

Washing up liquid to remove, wear a mask with a good filter and use an air purifier. Have a look at this re the cause. Be careful with mold, some people are sensitive to it and it can cause various health issues for those that are. www.heritage-house.org/Wah

Check the damp course on your brickwork outside. Is it there in the first place? Is it damaged? Is the mortar between your brick solid and in good state of repair? Has the damp course been bridged? Ie has soil piled up across it, or even just high enough for heavy rain to splash above it?

Just make sure all mould is removed before you paint as mould can live under paint - ask me how I know 🙄. Also some anti mould paints can't be painted over so read carefully if that's what you want to do. I definitely recommend a dehumidifier and avoiding having anything damp in there like clothes drying. Also no furniture against the outside wall.

Most of the mould cleaners are just extra strong bleach ( sodium hypochlorite) so I really wouldn't worry about having used bleach on the wall. Vinegar is nicer though and also does the job.

Once you've worked out why it's happening and fixed that, and cleaned it off, you can buy mould stop paint up use as a base coat.

Is it an outdoor wall? Condensation?

We run a dehumidifier upstairs.

Even so I found mould under our coats the other day, all over all the coats, all over the wall. It's an outdoor wall and it's single layer brick no cavity wall in that spot.

Plants.

This Mould Magic works very well and mould does not return quickly. But need to identify cause as well.

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@Nc546888 breathing too much?!?! That's a new one :)

I lived in student housing once and all the walls wet and mouldy. I tried bleach so many times.
the landlord refused to come out, kept saying it was my washing or breathing too much. Turns out there was a ginormous hole in the roof. I agree with others you need to find the root cause, there likely will be one

I used to use a window hoover to get rid of condensation, decent mould remover, anti mould paint too
Good luck

You could try a PIV unit.

I've used a spray called HG Mould Spray and Remover and repainted the room with anti mould paint. Windows open, dehumidifier running and those little £1 throwaway dehumidifiers in the corner under the furniture.

Are you drying laundry indoors? Shut the windows and put the dehumidifier on 24/7. Need much more info - are you ground floor is your garden higher than the DPC, is the bath leaking, could be a million and 1 reasons

We have those humidity readers , they are effective and cheap .

As a few people mentioned above, you need dehumidifiers and those cheap little digital humidity readers. See what the humidity is to start with and then start running the dehumidifiers with the windows kept closed. Opening windows when the outside humidity is 60%+ just exacerbates the problem because the outside air is even more damp.

I’d try this before hiring anyone or hunting for other sources.

A dehumidifier (a big one) is your best friend in this situation

If you replaster it will introduce literally gallons of water into the house while the plaster dries out. It's a really really bad idea if your aim is to fix mould without doing anything else.

You need to be heating the house properly and consistently so there's no condensation on cold surfaces, you need to be ventilating so that damp air form cooking, shower/bath, and just breathing is able to escape the house, you need airflow around the walls - don't have furniture up against walls, don't dry washing indoors, don't have stuff up against the walls outside either, especially if you don't have a cavity wall or you have cavity wall insulation - log piles, bin storage, sheds, shrubs and plants - all will trap damp and make it harder for damp from inside to get out even if it's not directly making damp from outside track inwards. If there's specific spots on the ceilings that are getting mould, you could check in the lodlft to make sure the insulation there is even, so not making a cold spot and also check it's not doing the opposite and there's too much so it's bridging the cavity and tracking moisture from the outside.

You could hire an infrared camera and use it to look for cold spots inside and hot spots outside to show where your insulation needs improving.

Dehumidifiers are great, but be aware it will pull moisture from the sink traps / loo, I avoid using ours in the bathroom and kitchen.

Get some HG mould spray. It doesn't remove the problem, but helps for sure. Maybe lasts longer at keeping it away that bleach.

Inadequate ventilation is a primary cause of black mould.

Tropical fish tanks and drying clothes indoors (over radiators etc.) add to the problem.

If you feel you have done all you can by means of opening windows and having heating on; a Positive Input Ventilation (PIV) unit may be an option for you.

Look at heritage house for free advice about damp.

2 dehumidifiers on average small home
3 above 70 sq m, on non stop in winter.
Repaint the worst patches in May

There is no amazing way to deal with it once and for all if you don't have money to pull down the whole infested structure and rebuild it