Black mould problem

With an older property and solid walls, it’s important to identify the cause properly before applying any waterproof coating or sealer externally. Black mould internally is often linked to condensation and cold wall surfaces, but if it is mainly on the rendered gable end, there could also be penetrating damp, failed render, cracks, porous brickwork, defective pointing, or trapped moisture within the wall.

I would be cautious about applying a waterproofing solution straight onto the outside wall without a proper assessment. On older solid wall properties, the wall still needs to breathe. Some waterproof coatings can trap moisture inside the wall and potentially make the problem worse if the cause is not dealt with first.

The best approach would be to inspect the external render, pointing, rainwater goods, ground levels, ventilation, and the internal wall conditions. Once the cause is confirmed, the correct solution may be render repairs, breathable external protection, improved ventilation, insulation, mould treatment, or other damp remedial works.

Dry Core Solutions would be happy to carry out a full free damp assessment and provide a written report with our findings and recommended works, so you have clear advice on the right way to resolve it.

Dealing with black mould from a rendered gable end on your solid-walled old property can be frustrating, especially with all the conflicting advice you've received. Let's cut through the confusion.

What's Causing the Mould?
The mould is likely due to condensation or penetrating damp, rather than "rising damp," which is often misdiagnosed. Solid walls breathe, and using impermeable materials like modern cement renders or waterproof coatings can trap moisture, leading to mould and structural issues .

Solutions to Consider:
• Improve Ventilation: Enhance airflow around and inside your property to reduce moisture buildup. Consider installing extractor fans in high-moisture areas like kitchens and bathrooms.
• Breathable Treatments: Instead of waterproofing solutions, opt for breathable renders or lime-based plasters on the exterior. These allow moisture to escape while protecting the wall.
• External Repairs: Check and repair any damaged render, cracks, or faulty guttering on your gable end to prevent water ingress.
• Internal Treatments: For interior mould, use anti-mould paints or treatments and ensure good ventilation. You might also consider dehumidifiers to control indoor humidity levels.
• Avoid Impermeable Coatings: Steer clear of products like acrylic or emulsion paints and waterproofing compounds, as they can exacerbate moisture problems .

Use a breathable waterproofing on the outside and check for cracks. Improve airflow inside. Don't use non-breathable sealers on old walls. And use damp seal!

No, avoid waterproofing the outside of solid walls with impermeable coatings — it can trap moisture and worsen mould. Instead, use a breathable, lime-based render or masonry paint to allow the wall to breathe and dry out. Also address any external defects (cracks, leaks, blocked gutters) causing moisture ingress.

Hi
You can use a water proofing solution on the out side .but you must make sure there are no cracks or damage to the render .before applying.
Regarding the black mould it's more likely to be caused buy poor ventilation .

Hi I have used waterproofing solutions on exterior walls for the last 15 years and I haven’t had any problems with it yet it is a cost affecting way to prevent damp ingress

Hello the new render needs to be a lime based render to allow the stone walls to breathe and moisture to evaporate otherwise moisture will build up in the walls degrading them and causing damp within your property. Brickwork block work walls you can use the same render with a waterproofer to protect the walls from penetrating damp as the walls aren't as thick as stone walls. hope this explanation helps you