"Why Is There Mold On My Basement Wall?"

That was the question I heard over the phone when someone needing a thermal image inspection, among other things, called to find out about possible foundation leaks.  They had this problem once before and were upset at having to deal with it again.

As to foundations, it is not a question of whether it will leak.  The real question is when?   Then you figure out why.

Mold, as you know, is not the original problem.  It is a symptom of the real problem.

When you discover mold(s), you must figure out where the moisture that encourages them comes from.

As it turns out this mold problem was in fact caused by accumulating moisture, seen clearly in the thermal image.  This wall demonstrates no staining, and does not feel wet to the touch.  But the mold had a squarish pattern, exactly the same size as the purple moisture presence you see here.  The most mold was located in the lower corner, where there was the most moisture, just as you see here.

But what caused the moisture?  This problem is on the front corner of the house, 10' below ground.

Outside I saw tall trees, gutters that had no caps and debris coming out of them, a downspout that discharges onto ground that inclines toward the house, and decorative grasses and ivy that hold moisture against the house. 

Let's get poetic with a little song (remember to make the creeping movement with your fingers as you sing):

The itsy-bitsy water went down the water spout,

And had no where to go when it finally came out.

Down, down the wall it would go on every rain,

Til the itsy-bitsy mold could all come out again!

My recommendation:  If you don't solve the cause of the problem the first time, it will happen again.  It is best to have downspout water diverted to discharge as far from the foundation as the landscaping makes possible.  That, and properly inclining soil to water is encouraged to flow away from the house, will go a long way toward keeping a basement drier.