Ghosting on Walls: Understanding the Causes and Solutions

The faint lines we see in the above photo are dust particles attracted to slightly damp surfaces - otherwise known as “ghosting”. The walls are insulated, meaning there's a layer of mineral wool insulation behind the painted plasterboard. This insulation sits between timber studs and nogs, leaving no insulation at the timber framing itself.  

Image showing mineral wool insultation and timber studs.

This construction method creates a thermal gradient across the wall.The insulated wall sections stay “warmer” than the timber studs, which have no insulation and will as a result lose heat faster, making them colder than the insulated part of the wall and makes the uninsulated parts more vulnerable to temperature changes. This temperature change, combined with moisture in the air, causes these faint lines – or “ghosting” to occur.

The air in our homes always contains a certain amount of moisture vapor, known as humidity, but problems can arrive when the moisture builds up due to influences within the dwelling adding to the humidity within the space combined with temperature changes due to heating. When this increase in heat occurs combined with an increase in humidity the dew point can be reached.

The dew point is the temperature at which warm moist air can no longer be held in suspension. Just like when water condenses onto the outside of a window. The cold glass drops the temperature of the surrounding air which gives up the suspended moisture and so water droplets form on the inside of your window.

image showing condensation on glass.

This same moist air might also contact the plasterboard wall where a timber stud is located. However, in this scenario the temperature change only has to be very slight and the same type of phenomenon can occur.  The warm, moist air releases some moisture onto the cooler stud/ plaster board junction. The temperature change between insulated wall and uninsulated plasterboard causes moisture to condense on the surface as a thin, damp layer the same width as the timber stud. This slightly damp layer attracts dust and other air borne particles, which shows up as the lines we see over time. 

Image of ghosting.

This increase in moisture comes from various sources: cooking, unflued gas heaters, bathrooms, laundry, and even breathing. We exhale a lot of moisture while sleeping. A Person breathing can generate up to 400 ml of water every 24 hours. 

The temperature and moisture changes don't need to be significant; the right conditions just need to exist. This issue often develops gradually and goes unnoticed for a while. Sometimes, a change in room use or conditions can accelerate the process. 

So, the problem might not be a water leak, but rather internally generated moisture.  

One solution is to encourage air changes within the home. This can be achieved as simply as opening a window slightly to encourage drier external air flow to the internal room or installing a ventilation system that will draw external air from the outside through the home thereby lowering the humidity level within the home in a controlled manner.   

Image of a ventilation system being installed.

In conclusion, the issue might not be a water leak, but rather moisture generated within your home. The AWC team specialises in identifying the causes of tricky problems like this. We can conduct a comprehensive assessment to investigate external factors and thoroughly examine your home's internal environment. Want to enquire about our waterproofing consultancy services? If you have any questions or would like to explore , get in touch.