Question: We noticed some mould-like patches on the ceiling of our washroom, right above the shower. It started with a small spot a year back and now has become bigger.
We got a handyman two months back to check it out and he said it’s mould. We changed our exhaust fan and put it on a timer since then. What’s your suggestion? If it’s mould, how do I get rid of it? Or do you think that it’s some kind of leak?
Looking forward to hearing from you. Thank you very much.
— Bindu Menon
Answer: Bathrooms are probably the most likely place in a home to discover mould, due to the large amount of moisture produced from bathing and showering.
The simple way to prevent mould growth is to minimize excess moisture. You may be part-way there with the fan upgrades, but other items may need to be addressed to fix the problem.
For mould to grow, there needs to be three basic items present. First, mould requires a cellulose-based food source to grow on. This may be anything from dust and dirt that forms on the surface of the ceiling, to the drywall or plaster the ceiling is made of.
In your case, the stipple that has been applied to the underside of the area makes it worse, as this material can collect excessive dust, dirt and other material ideal for mould growth. This uneven product also prevents easy cleaning and painting of the ceiling, and makes removal of surface mould harder. So, removing the food source to prevent mould is not an easy option.
The second item necessary for mould growth is heat, which is in no short supply in a heated living space, especially a warm bathroom.
While we can’t do much about that criterion, the final component, moisture, is well within your control to manage. While you are limited in your control of the growth medium and the heat required for mould to flourish, you should then concentrate on minimizing moisture to inhibit mould.
You have taken one good step toward that end, with replacing your ceiling exhaust fan. Installing a timer on the fan is another excellent idea, as you can run the fan for an extended period of time after a shower, even if you are not home. This will help remove excessive dissolved water vapour in the bathroom air. Also, leaving the fan on for an extended period may help prevent or dry condensation that forms on the surface of the ceiling, which may be your biggest problem.
There are two main possibilities for the actual cause of the mould formation on your bathroom ceiling.
The mould will grow on the underside of the ceiling, as discussed, if the humidity in the bathroom stays too high after use. If the ceiling is damp for an extended period of time, the dust trapped in the uneven surface, and the stipple finish itself, will provide perfect growing conditions.
If your newly upgraded fan operates properly, for an extended period of time, it should dry this surface moisture and take away the main condition for mould growth. You should ensure that this is working effectively by looking at the roof-mounted vent hood when the fan is running. The damper should be open and air should be felt blowing out the vent hood.
If your roof is easily accessible, carefully climbing up to check this out may be warranted. If minimal air is felt during this test, there may be a blockage or problem with the vent and repairs or replacement may be required.
The second possibility for the mould growth may be more serious and difficult to remedy.
Excessive moisture may be leaking into the area above the drywall bathroom ceiling, causing condensation and wetting of the top of the drywall. If this stays wet for any length of time, the drywall itself may become the growth medium and you are seeing only the underside of a larger problem. This is much more likely if the bathroom ceiling is the floor of an insulated attic. In that case, warm air from the bathroom may condense when it hits the cooler attic air, soaking the drywall and insulation. If the exhaust fan duct is running through this attic, and is not properly insulated and sealed, it too could cause this same scenario.
All of these items may be checked by accessing the area above the bathroom, through the attic hatch, and ensuring proper insulation, ventilation and a properly vented duct are present.
The removal or cleaning of the mould in your bathroom depends on how severe the mould growth is. If it is only on the surface of the drywall and stipple, and the attic inspection looks good, then minor repairs may do. With proper breathing protection worn, the surface mould and stipple may be scraped and washed off with a putty knife and sponge. If this works, there may be no need to go much further.
If the mould is embedded in the drywall paper or gypsum, it will have to be cut out and discarded. Removal of all the stipple, re-taping, sanding and painting should be the final steps in the project.
Removing the mould from your bathroom ceiling may require no more than scraping and washing the surface, and reducing the moisture in the bathroom with your upgraded exhaust fan. If it is due to leakage or condensation in the attic above, that will have to be addressed before the damaged drywall is removed and replaced, and the properly vented fan used to prevent a reoccurrence.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
