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:
Keep the whole world singing . . . .
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
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 /
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.
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
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
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
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:
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
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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