Q&A / 

Dark Stains on Stucco

Faith James has a nice home in Dallas, Texas. But now there are some ugly dark stains coming down from the roof onto her stucco.

Here's what she sent me:

"Hi, Tim,

After snow and rain I noticed black streaks down the front of my stucco home, coming from either the roof or the gutters.

Please look at this photo I took:

You can see the staining starting up at the parapet ledge. Photo credit: Faith James

You can see the staining starting up at the parapet ledge. Photo credit: Faith James

I have a roofer coming out to see which it is, but can you tell me how to clean this stain?

Sorry I can't get on top of the house to see where its coming from."

Guess what? I'm 99.999 percent sure I know the cause of the stains, Faith!

The biggest clue is you told me where you live - near a big city.

I'm quite confident if you were to pay to have a lab analyze the stain, much of it is just diesel engine soot.

I used to have the same problem on the painted siding of my home in Cincinnati, OH. Each year I'd have to wash off my house and I traced the black stains and grim to all the truck traffic on the nearby interstate highways and normal urban traffic of heavy trucks.

You can clean off the stains and restore the stucco to like-new appearance with my Certified organic Stain Solver oxygen bleach.

The Stain Solver is NON-TOXIC and it will not hurt any of your great landscaping like chlorine bleach will. Don't use chlorine bleach or ANY product that says it contains sodium hypochlorite.

It's a powder you mix with warm or hot water and you spray it on the stucco with a hand-pump garden sprayer.

You work in the shade and saturate the stucco with the solution for 15 minutes. You then lightly scrub it with a brush, rinse and it should look fantastic.

I sometimes add a squirt of liquid Dawn dish soap into the Stain Solver solution.



2 Responses to Dark Stains on Stucco

  1. I've inspected hundreds of stucco structures. The stains are what I refer to as water fall stains. Looks like it may have a parapet (section of wall that extends above the roof) and water is flowing down off the parapet onto the side. The top of the parapet should be sloped toward the roof structure (away from the wall) at least 12 degrees to prevent the water fall. Appears from photo that parapet above area where slope changes is not sloped and where water reaches the elevation change, it overflows onto the side. After correcting problem, clean or paint the stucco. There are particulates in rain no matter where you live - may be diesel, coal dust or hundreds of other reasons. A cheap solution may be to create water divertors using clear silicone caulk to direct water onto to roof vs the side.

  2. SUPPLEMENT: this structure may also have a slope problem on the decorative band above the column. It too, along with any other trim should be sloped away from the wall. Water is also hitting the street number sign (note the water fall stain splits below it). This is a problem no matter if this is concrete based stucco or EFIS (exterior finished insulated siding). Water will find a way to penetrate through the sign fasteners into the sheathing/framing causing structural damage. It may take years, but it will happen. In concrete stucco, it can cause the extruded metal used to attach the stucco to the sheathing to rust (requiring a tear off to facilitate repair), as well as tear off and repair of structural damage whatever type siding is used. A bead of clear silicone above the house number will help mitigate by directing water away from the back of the number plate and fastener penetrations. THIS IS POTENTIALLY A SERIOUS PROBLEM!

    WATER DIVERTER: Don't know if your readers know what this is - a water diverter is something that directs the flow of water. It can be an L shaped peice of metal installed on a shingle roof to direct water away from siding etc., but in this example I recommend that a bead of clear silicone caulk be applied in multiple areas diagonally on top of the parapet that directs water flow away from the wall (top of bead higher than lower end). It will not be visible from ground level. I would even suggest a silicone bead be applied above the entire outer edge of the parapet to force water toward the roof.

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