To not know what to do about mold, please help

[TheStepboardisfullofbitteroddos]

There's mold in my baby's room. It's a box room and mold appears on the 2 external walls above the skirting board. We clean the wall and remove it but I've found that it's under the top layer of paint. Which is silk paint so trapping the moisture. Room is currently empty and no visable mold.

Builder says we need to take the wall back to brick and then board and replaster. It's so expensive. I don't know if this is the correct thing to do. Has anyone had similar issues? Someone else mentioned stripping the silk paint, using chemicals to kill the mold and then fix the underlying issue.
Back to brick seems really extreme and messy so won't that spread the spores rather than kill them?

It's a solid brick 30s house. We have a render issue which we are planning to fix in a couple of months- we assume that the underlying cause of the moisture.

I think you’d need to do the render and infernal walls at the same time to stop it happening again

For a short term solution, buy a dehumidifier with smart setting and run it 24/7. I'd recommend Ebac.
No More Mould

Definitely get a dehumidifier in the short term.

How many dehumidifiers are you running?

Is there a structural problem with the house that needs fixing? Broken gutting? Leaky roof?

Or is it just poor ventilation and too much condensation? If it's that, then move any furniture away from the walls where the mould grows. Open the trickle vents on the window or lock them open a crack. Keep the radiator on in that room and the door open. Get a dehumidifier. Don't dry washing in there. Wipe down any condensation on the window daily. Use HG mould cleaner to treat the mould. Then repaint with anti mould paint. It's a yearly battle in 1930s houses. The mould does come back, just keep on top of it.

It sounds like parts of my house, definitely connected with old render - there is more than enough ventilation here! Someone told me there is a plaster you can get that prevents moisture coming through to the walls and affecting the inside, although I'm not inclined to do it without repairing the render as it won't solve what's going on on the outside and he said as much. There is also a Zinsser paint you can get that I have in my bathroom that stops all mould but I personally would be cautious using it in a baby's room.

If you remove the plaster now then the wall can start to dry out.
However you cant fix the problem until render is repaired and the wall dries out.
The wall will take a while to dry out before it can be replastered, i think the estimate is 1month for each inch of thickness of the wall so it is worth removing the plaster now.

Might be worth using the opportunity to add some external wall insulation at the same time but only once the wall has dried out.

Assuming the outside wall is in good condition with no cracks in the bricks/mortar then unfortunately the only way to fix the problem is take the walls back to brick.

It doesn't have to be messy or expensive but it really does need sorting ad you'll only be wasting time and money long term.

Don't whatever you do use bleach, it may wash away the mould at first but it can actually cause more problems.

You've not mentioned anything about ventilation. What do you do throughout the house to reduce moisture? Open windows? Dehumidifier?

Whats the outside wall like. Does it need repointing? Is guttering OK?

I can't recommend Killrock spray enough, I had tried every brand and method going until this finally did the trick. Always finish off with the preventer spray after, it's amazing stuff.

Thanks for all the advice!

Windows are open every day for at least an hour in the whole of upstairs And generally that bedroom window is left on the latch at all other times. There is a small leak in the roof on the other side of the house that is being fixed in a few months. But it's completely dry on the side of the bedroom. Because of this we are running a dehumidifier in the loft all the time. We also run one downstairs in the utility to dry laundry. They are both big decent ones.

However the room isn't damp it's about 50-60%. We pulled skirting off and removed carpet, underlay and floorboards. There's no sign of damp or more mould. So planning now to heat gun paint off wall, kill mould and zinsser.

The best anti-mould spray there is, is HG. It’s like witchcraft!

If your house is solid walls then the mould is due to trapped moisture. Using Zinsser will not solve the problem, and will make it worse! Solid wall houses are meant to breath so moisture can move through walls, using plastic paints and render traps the moisture and causes mould.