Stained Stucco Under Window

Some of windows on this house have discolored stucco at the corners under the window. Some have a visible crack. We had several days of rain prior to this picture. Can anyone explain this?
Thanks Andy
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Improper flashing of the windows.
How old it s this place? You don't say, but I suspect you may have EIFS rather than traditional stucco. Sadly, poor flashing is quite common on all construction but is really bad on EIFS installations by poor applicators. The only solution to my knowledge is to rip the wall open enough to correct the flashing and house wrap around the window. If the stud wall below the window has been saturated enough times, it may well require replacement. This is not something that can be fixed by smearing a little caulk on the outside.
Here is some good reading: <http://www.jlconline.com/cgi-bin/jlconline.storefront/47860569000e4d8e27177f0000010561/Product/View/0102maki
<http://www.jlconline.com/cgi-bin/jlconline.storefront/47860569000e4d8e27177f0000010561/UserTemplate/82?sG860569000e4d8e27177f0000010561&cYe803a8ea012192b91c88f3be8e5dff&p=1
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Andy,
I've seen a lot of houses like this in my area. In one that I inspected closely, it appeared that they applied the stucco directly to the wooden sill. The wood of the sill changes shape at a different rate than the stucco, leading to cracking, particularly at the ends. The moisture builds up in the wood, leading to wood rot. The rotting wood, provides further nutrients to algae/mold as it seeps out of the crack and drips down the wall, leading to clear wall staining patterns.
See:
http://www.etccreations.com/DSC_0066.JPG
This is also visible in many windows where there is no stucco problem. Vinyl clad windows can trap water behind the vinyl. Since the vinyl is impermeable to water, the water absorbs into the wood faster than it evaporates to the outside. Some water will drip out at corners and seams, as in the picture linked to. Ultimately, this leads to rot / window failure.
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Is the stain about the same color as the window frame paint? If so you may need to re-paint the window and power wash the the stucco. Then apply some caulking to the cracks and waterproof the stucco with Thompsons or some other water repelant.
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1) This house is 17 years old. 2) I do not know if it is real stucco, I do have a picture of a damaged window sill and a damaged cornner. I'll post tem as soon as I can and maybe someone can tell me if its really stucco. 3) The windows are Aluminum and white in color
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Do NOT "waterproof" the stucco! Stucco, and other masonry siding, is water permeable, and should be maintained permeable. There is a common misperception that siding is a waterproofing layer - it is not. Stucco, and other siding products, are aesthetic and physical barriers, representing the outer skin of your home. But they also allow water to get behind them, and that must be allowed to escape easily or it may rot out the underlying wood sheathing.
Any stucco siding will have numerous micro-cracks, these are normal and are not the cause of water damage. What causes the damage is improper flashing and drainage plane assembly. Both must be done properly, or water will get behind the drainage plane and get trapped in contact with the wood sheathing and likely allow bulk water entry into the walls of the home.
For an excellent discussion of the topic, read the literature on mtidry.com
However, this is all mainly academic. Your problem is very likely, as noted, caused by moisture problems in your window framing or framing around the window. At the lower corners of the window, where the staining occurs, poke any wood you can see exposed by cracks. If it is soft and/or wet, you've got a problem that needs to be rectified before it gets worse. There are some excellent articles on-line on fixing rot. See: http://www.thisoldhouse.com/toh/article/0,,680938,00.html
Stucco is very tricky however, because you can't just pull off a piece and repair the rot because the proper layering of flashing and weather resistive barrier is critical. Unfortunately, very few builders truly understand the importance of this, so repairing it properly can be a challenge.
If you can, post a close up of the area where the discoloration shows and a high resolution picture of the entire window area of the wall, so we can see what the general construction of the area looks like.
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