May 30

Is it mildew or is it dirt?

Mildew on exterior of house

Mildew on Exterior of House

A DIY Guide to identifying and properly eliminating mildew before exterior painting.


While mildew and dirt may look the same on the exterior of your home, proper cleaning before painting is a must to ensure a long-lasting exterior paint job. Water is always the source of mildew.  Avoid the temptation to just wipe away mildew and forget it, find and eliminate the water source or mildew will keep coming back.

Mildew tends to grow on the exterior of houses where surfaces receive little or no sunlight, damp environments, and warm moist weather where the absence of freezing temperatures fosters mildew growth.

 Is it mildew or dirt?

Here’s a quick test to find out.  Place a few drops of diluted bleach on a small section of the discolored area, wait a few minutes before rinsing.  If the stain fades, its mildew; bleach will not affect dirt.

 It’s mildew, now what do I do?

Never paint over mildew.  Remove it first by applying a solution of bleach diluted with water (3:1).  Always remember when using bleach to protect your eyes, skin, and avoid breathing in directly.  Protect surrounding plants and grass by wetting them down and/or covering them.  Leave bleach solution on the surface for 20-30 minutes, re-apply if it dries, rinse thoroughly.

How can I avoid mildew in the future?

The best way is to prevent it!  A clean, dry, light-filled environment discourages mildew development.  Trim surrounding shrubbery to ensure proper air circulation and fix any standing water related issues (dripping air conditioners, misdirected sprinklers and leaky gutters).  Regularly power wash the exterior or your home with a bleach solution or commercial product formulated to inhibit mildew growth.

What’s the best paint to inhibit mildew growth?

Latex is better than alkyd and oil-based paint and satin formulas are generally more mildew resistant than flat paints.  A top quality paint is likely more mildewcide than a lower grade paint.  Use a mildew-resisting additive only if recommended by the paint manufacturer.  Check with your local paint store for exterior paints specifically formulated to inhibit mildew growth.

Did you know, dark colors dry out faster (dew, rain), so tend to support mildew less.  Also, paint applied with a sprayer can be better than brushed (brush marks can hold onto nutrients for mildew and mildew can collect there.  (Information cited from www.paintquality.com – The Paint Quality Institute.)

Some Final Thoughts.

Exterior mildew removal and proper paint application may be best handled by a professional painting contractor.  If you live in Lake County Florida or surrounding areas, give us a call at (352) 702-5119, visit our website for more information www.qualityassurancepaintinginc.com

Have you had an experience with exterior mildew growth on your house?  Share your experiences in the comments section below.

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About the author

Tim Grubbs

I am the owner of Quality Assurance Painting, Inc., serving Lake County Florida and surrounding areas since 2005. I am an experienced professional painter and coatings specialist. I do both residential and commercial work for myself and as a subcontractor to general contractors. We strive to set ourselves apart from the competition by providing 100% customer satisfaction in both workmanship and customer service. My knowledge in the industry continues to grow by reading about new products and techniques and participating in seminars and webinars. We specialize in interior and exterior repaints for both residential and commercial properties, plus waterproofing techniques. We are an A rated members of the Better Business Bureau and 2013 PDCA (Painting and Decorating Contractors of America) members. We provide free estimates to our customers and are fully insured and licensed.

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