Garage wall mould

Question

I’ve got a garage in the garden and in the summer I decided to fix OSB3 to the internal wall and paint it with a wood primer which is water based to make the wall look tidy since the person who plastered it didn’t do a good job. Now that winter is here I’ve noticed mould growing on parts of the wall. What can I do to fix it apart from using mould removal spray, looking for a permanent solution.

Lee · Answer

To fix the mould issue in your garage permanently, focus on addressing moisture ingress and improving ventilation:

1. Identify and Fix Moisture Sources
	•	Inspect for leaks in the wall, roof, or around windows and doors. Seal cracks and gaps using a waterproof sealant.
	•	Improve drainage around the garage to prevent water pooling. Clear gutters and consider adding a French drain if necessary.

2. Improve Ventilation
	•	Install wall or louvre vents to encourage airflow and reduce condensation. Place vents on opposite walls for cross-ventilation.
	•	Use a portable dehumidifier to manage moisture levels, especially in winter.

3. Upgrade Wall Treatment
	•	Remove the OSB3 panels to inspect and clean the wall. Treat it with an anti-mould solution and ensure it’s completely dry.
	•	Apply a vapour barrier (e.g., polythene sheeting) between the wall and OSB3 to stop moisture from reaching the panels.
	•	Use a mould-resistant primer and topcoat on the OSB3 panels or replace the wood primer with a water-resistant, anti-mould paint.

4. Add Insulation
	•	Insulate the wall with rigid foam board or insulated plasterboard, leaving a small air gap between the insulation and the wall to allow moisture evaporation.
	•	Ensure the insulation material is breathable and suitable for garages.

5. Replace OSB3 (Optional)
	•	Replace the OSB3 panels with more moisture-resistant materials such as treated plywood or cement boards if moisture persists.

6. Prevent Future Issues
	•	Regularly check for moisture or mould and maintain proper ventilation.
	•	Keep the garage decluttered to improve airflow.

These steps will create a drier and mould-resistant environment, ensuring the problem doesn’t recur.

Steven · Answer

This will be due to the cold air getting inside the building. You could remove the ply insulate it and get some form of heating and ventilation to regulate the temperature inside the garage.

Alex · Answer

You need to add an air vent, moulding probably because of poor air ciculation.

michael · Answer

You should have batten the walls, fit insulation ie kingspan.then a moisture board on top

Anthony · Answer

Sorry to hear this. 
However you need to make the internal walls warm by adding insulation behind finished wall.

This is a common problem in homes nevermind in an outbuilding where there is no heating .

Kieran · Answer

You should’ve use some Battens An installation first

Oleksandr · Answer

Good evening,
• you have a cold wall, that's what you're going to get rid of now. To get rid of it you need to insulate and put a membrane

•maybe there's no ventilation in your garage and it's all steaming up

Kash · Answer

Mould is usually caused from a lack of ventillation and lots of condensation build up. It requires airflow once you wipe and clean it to prevent it from coming back again.

KASH 
Weknowhow

Garage wall mould

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