This CMU foundation has a moisture or algae stain on the second course down from the top. The second course is stained around the whole house, except at the deck. The first picture is under the screen porch. The staining is present on the foundation walls the roof eave and roof gable. I can’t come up with a good explanation, which is how I left it in my report.
It’s a high efficiency northern climate home with stud wall construction. I speculate there is spray foam in the stud wall above the foundation. The basement is studded inside with closed cell spray foam visible (and not yet covered with drywall). It’s a low pitch roof with no gutters, although rain is channeled by diverters on the roof. Image #2 shows staining on the top course, near where roof runoff is channeled by a diverter. I could not view the rain barrier where the siding meets the foundation wall. In retrospect, I should have checked moisture of the block with a moisture meter, but dark colored block makes a statement by itself.
Maybe how the blocks were stored prior to installation? Working from the top down on the stack of block, the rows in contact with the ground would be higher up the wall (I know this is the least likely explanation)
I was considering bond beam being a factor. I don’t understand the moisture movement component; Maybe you are thinking the source might from the ground??
The top of the block was not exposed in the basement. It was sealed with spray foam insulation in conjunction with sealing the rim joist and foundation wall interior.
Lacking gutters, I speculated rain from the roof was a component. However, the gable end of the foundation has the same phenomena. At the same time, the moisture in image two, arrow on the top left, is in the same area where roof runoff is concentrated by diverters on the roof that channel and concentrate roof runoff.
Morning, Michael.
How do you know it is moisture? Any comparative measurements?
How do you know it is algae? Any laboratory report?
IMO; At this stage, I would consider this no more than an ‘anomaly’ for I do not like reading too much into how such a thin evenly patterned stain was formed.
What was on the other side of the wall? Ledgers?
Look at the composition of the anomaly. Thin evenly banded stain, say 3" inch deep, just below the head of the top CMU.
Going off thread a bit.
When I worked masonry, and installed block, when we reached the top course, or as much as we could do that day, we covered the top CMU wall with temporary coping flashing using 15lb felt, nonperforated tar paper, to prevent water/moisture from entering, and then stacked at least 1 mortar-less CMU on top of the wall to weigh down the CMU just laid so they can bond to the mortar evenly.
Going out on a limb I would guess that the dark banded shadow line was from atmospheric grime that got trapped under/behind the temporary flashing.
What would I report?
Observation: Thin even band of dark staining, of unknown origin, on the CMU wall.
Recommend: Refer a licensed masonry contractor for further analyses.
Act upon any referrals offered.
I just found out this is an old foundation used for the 2009 new build. I also found out who the builder is, who I know and have worked with when I was a contractor. Excellent builder. The buyer got a chance to talk to the original builder.
The cause remains a mystery. I used a narrative similar to @ryoung7. Thanks for all the replies. Happy 4th and happy Canada Day.
(I know this is the least likely explanation)
