Advice from Commercial Painting Experts on Fixing Mould

Tips from commercial painting professionals to help with your DIY painting problems. Programmed Property Services are the largest employers of painters in Australia and New Zealand. We have a huge knowledge base we can draw from to answer any painting related question. This month, we look at how to fix areas affected by mildew and mould.

commercial painting

by Nathan D’Couto

How to identify mildew and mould
Typically, mould is either black, grey or brown spots on the surface area of paint. Mildew is most common on external painted weatherboards and is very similar in appearance.  Both are caused by damp and little, or no, exposure to sunlight. This is very common on the underside of external eaves and weatherboards in shaded areas, as well as in wet areas like laundries and bathrooms commonly caused by poor ventilation.

Other causes of this problem include:
* Poor quality paint not containing adequate amounts of mildewcide. This is an additive normally added by paint manufacturers designed to inhibit mold and mildew growth.
* Failure to prime bare wood before painting.
* Applying paint over existing mould or mildew which has not been removed.

Solution
Safety first: mould is a fungus and when airborne can be harmful to children, the elderly, those with a weakened immune system, or other medical conditions such as respiratory conditions like asthma. Ensure you have a good quality dust mask or respirator, full length clothing, rubber gloves, and goggles.

Preparation
Start by testing the area to ensure it is mould or mildew. Apply a few drops of general undiluted washing bleach to the area in question. If the discoloured area starts to disappear and the paint surface reappears then we are definitely working with mould or mildew.

Mix one part household bleach with three parts water and start applying it to small areas using a scouring pad. Keep scouring the area until all evidence of the mould is removed.  Then rinse the area with water. If treating an external area sodium hypochlorite can be used at a 1:3 ratio. For much faster results rinse with a pressure/power washer.

Painting
Our Paint Pros recommend using premium grade oil based sealer / undercoat to all affected areas. Most paint manufacturers say you can apply their products directly without an undercoat over these areas, but our paint pros tell us if you don’t want the mould to reappear use oil based undercoat first.

After this step apply 2 coats of premium acrylic paint suitable for the area. There are many paints on the market that claim to resist mould. Our commercial painters say any premium grade semi gloss acrylic paint will do the job if the area is prepared and primed well prior to top coating. For external areas a suitable external grade semi gloss or gloss acrylic is recommended.

To prevent mould from reappearing ensure your wet areas are well ventilated (install an exhaust fan to improve circulation). For external surfaces, washing painted surfaces with a mild detergent every 12 months will almost guarantee you will have a mildew free surface.

Programmed Property Services are the largest employers of painters in Australia and NZ. With over 700 fulltime painters and 40 apprentice painters, we have a huge knowledge base we can draw from to answer any painting related questions.

So if you’re facing a paint problem or want to know how a commercial painting professional would do a particular task, why not ask us?


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  1. my fountain which was a dark grey colour has faded with age and water use. i have emptied and brushed it down. what paint can i use to spark it back to life. i also have statues on both sides of my fountain which where grey and needs a paint. please help me to improvethe look of them. thank you. regards, margaret

    1. Hi Margaret,

      If the fountain wasn’t originally painted, we would recommend going to a hardware store like Bunnings and get some caustic soda and follow instructions. Brush this onto the fountain and pond faces and leave it be for an hour. You should then rinse all surfaces with a pressure washer or high pressure hose.

  2. Hi, your advice is spot on, (but I’m sure you knew that). The areas I undercoated with oil-based sealer-bonder are mould free.
    Unfortunately, I learnt on the journey, and the eaves suffered.
    I cannot scrap them back to bare asbestos, and I’m now of an age where washing them annually will soon be a task that’s not achievable. We both have respiratory problems.
    Can I wash them, then coat with sealer-bonder? Will this keep the mould away?

    Thank you immensely for being there for L-Plate painters, like myself.
    Greatly appreciated.
    Lin

  3. house painted 1.5 years ago. Latex based paint. Mildew under the eaves is an increasing problem. Bleach washing every two to three months now. Without completely starting over with paint, is there some coating that can now be applied to retard or prevent the mildew from returning?

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