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MarcomitZeh13 Sep 2025 07:25Hello everyone,
This concerns a single-family house built in 2004/2005. At one spot in the wall plaster, there are strange deposits visible, see photo. According to the documents, a “colored stone plaster No. 900 with a grain size of 3 mm (0.12 inches)” was applied to the base area, and on the house wall a “Terrastar 222 disc plaster light 3 mm (0.12 inches).” Around the house, a 40 cm (16 inches) wide eaves strip filled with gravel has been laid. However, in front of it are flower beds with many hydrangeas and other larger plants, some of which cover the edge of the eaves strip and in some cases reach almost up to the house wall. The stain varied from gray to brown to slightly pink.
At first, I thought the pinkish color might be caused by algae due to shading on the wall in this area (the wall faces directly north). However, these stains do not appear anywhere else along the same wall, so it can’t be solely due to the northern exposure. Also, there are no plants directly at this spot. My second guess was that the previous occupants had a permanently installed hose system to water the flower beds, and over time, the (quite iron-rich!) well water was sprayed uncontrollably onto the wall. The shape of the stain could support this idea: to me, it looks like stalagmites growing upwards from the floor of a cave. A watering system might have sprayed several thin water jets at the same points on the wall repeatedly, from where the water then ran down in a widening streak.
Yesterday, I applied a generous amount of Biostein with a brush onto the damp wall (for those unfamiliar with Biostein: a very effective household cleaner that removes most stains), let it sit for about 15 minutes, and then scrubbed. A strong ocher-yellow liquid ran down (unfortunately, I didn’t take a picture of it in my enthusiasm for scrubbing). The last photo shows the scrubbed wall, still slightly damp and not fully dry yet; the remaining stains do not come off further.
What do you think about the algae theory? What do you make of the permanently installed watering system idea? What other causes for this kind of damage come to mind? And: which of these is most likely, and why?
Thank you very much, and best regards,
Marco
This concerns a single-family house built in 2004/2005. At one spot in the wall plaster, there are strange deposits visible, see photo. According to the documents, a “colored stone plaster No. 900 with a grain size of 3 mm (0.12 inches)” was applied to the base area, and on the house wall a “Terrastar 222 disc plaster light 3 mm (0.12 inches).” Around the house, a 40 cm (16 inches) wide eaves strip filled with gravel has been laid. However, in front of it are flower beds with many hydrangeas and other larger plants, some of which cover the edge of the eaves strip and in some cases reach almost up to the house wall. The stain varied from gray to brown to slightly pink.
At first, I thought the pinkish color might be caused by algae due to shading on the wall in this area (the wall faces directly north). However, these stains do not appear anywhere else along the same wall, so it can’t be solely due to the northern exposure. Also, there are no plants directly at this spot. My second guess was that the previous occupants had a permanently installed hose system to water the flower beds, and over time, the (quite iron-rich!) well water was sprayed uncontrollably onto the wall. The shape of the stain could support this idea: to me, it looks like stalagmites growing upwards from the floor of a cave. A watering system might have sprayed several thin water jets at the same points on the wall repeatedly, from where the water then ran down in a widening streak.
Yesterday, I applied a generous amount of Biostein with a brush onto the damp wall (for those unfamiliar with Biostein: a very effective household cleaner that removes most stains), let it sit for about 15 minutes, and then scrubbed. A strong ocher-yellow liquid ran down (unfortunately, I didn’t take a picture of it in my enthusiasm for scrubbing). The last photo shows the scrubbed wall, still slightly damp and not fully dry yet; the remaining stains do not come off further.
What do you think about the algae theory? What do you make of the permanently installed watering system idea? What other causes for this kind of damage come to mind? And: which of these is most likely, and why?
Thank you very much, and best regards,
Marco
My first thought is rising damp; after scrubbing, that suspicion remains. The moisture barrier beneath the exterior wall might be damaged. I would call a professional now while the damage is still manageable. Walk around the house to check if this is the only affected spot. Which direction does it face—windward side?
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nordanney14 Sep 2025 11:58Now the question here?
The answer will likely be that it looks like typical dirt and algae buildup. No rust is visible. Rising damp might also be a possibility.
The answer will likely be that it looks like typical dirt and algae buildup. No rust is visible. Rising damp might also be a possibility.
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MarcomitZeh14 Sep 2025 11:59Nida35a schrieb:
my first thought is rising damp,Does it fit that the other side of the wall, around the corner to the right (clearly visible in photos 1 and 2), is completely intact? Shouldn't it also be damp and show signs of mold there? The wall faces exactly north.
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MarcomitZeh14 Sep 2025 12:01nordanney schrieb:
There will also be the answer that it looks like typical dirt buildup and algae growth. Only this one single spot on the entire house? Everywhere else just the usual dust deposits? Does that make sense?N
nordanney14 Sep 2025 12:31North-facing and located behind plants is ideal for this. It frequently gets wet and hardly dries because no sunlight reaches it. You can observe this in any new construction area.
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