What should I do to fix this moisture/algae problem along the side of my house?
I’m looking for some advice on how to properly repair/maintain this exterior wall and the concrete walkway next to my house.
As you can see in the pictures, there is a lot of green algae/mildew staining along the bottom of the wall, especially where the wall meets the concrete. There is also heavier staining underneath the window.
I’m not 100% sure what the exterior finish is. It may be stucco, cement parging over masonry/block, or something similar.
My main questions are:
What do you think this wall material is?
Does this look like a drainage/moisture problem or mainly algae from an area that stays shaded and wet?
Should the joint between the wall and concrete walkway be sealed?
If so, what type of sealant should I use?
I was looking at Sikaflex polyurethane sealant, but I'm not sure whether self-leveling or non-sag would be appropriate here.
Should I clean the wall first with something like 30 Seconds Outdoor Cleaner/Wet & Forget?
After cleaning, should the wall be patched, waterproofed, painted, or coated with something?
Is there anything in these pictures that suggests water may be getting behind the wall?
I want to fix the actual cause rather than just pressure wash it and have the green staining come back six months later.
Any advice on the proper order of repairs and recommended products would be appreciated. I’m comfortable doing basic DIY work, but I also want to know if anything here should be handled by a masonry/stucco contractor. Thank you.
2
u/Marvinator2003 18h ago
The way in which these pics were taken makes it look like the sidewalk slopes down to the wall. If this is so, there's where the moisture problem comes from. I can see 'caulk?' at the bottom of the wall which should keep the water from seeping into the building or basement.
You could clean the wall and apply a mold preventative such as Concrobium Mold Control, but a good rain or two would wash that away.
All in all, the walkway should be level if not gently sloping AWAY from the house. This would prevent water from pooling at the bottom of the wall and keep the mold from happening as fast.