ᐅ Plaster facade with external thermal insulation composite system (ETICS) using mineral wool – brown stains
Created on: 13 Feb 2023 21:27
W
wp.seeker
Hello everyone,
Our house was insulated and plastered between early and mid-November 2022.
The insulation is Rockwool Coverrock II, followed by a base coat, reinforcing mesh, top coat, and facade paint.
About two weeks later, brown spots appeared in various places, irregularly distributed on all sides of the facade. There are small spots and larger spots up to about 10cm (4 inches) in diameter, some pale, some intense brown-red. Over the course of 2–3 weeks, more spots showed up, but now no new ones seem to be appearing.
Has anyone had experience with this?
An online search suggested it could be moisture penetration dissolving the binding agents and fillers, or phenolic resin residues, resin pockets in the mineral wool boards themselves somehow coming through.
During the facade work, there were a few brief rain showers, so it’s possible the mineral wool got wet.
However, against the moisture penetration theory is that some spots appeared directly under the eaves, places that couldn’t have been exposed to rain, or on areas that were only installed after the rain. Overall, we had a very favorable weather window for that time of year.
The very irregular appearance could support the phenolic resin residue or resin pocket explanation. As far as we can tell, it’s not related to the board edges or possible fixing points.
Has anyone observed this phenomenon before and how was it resolved?
Thank you very much
Our house was insulated and plastered between early and mid-November 2022.
The insulation is Rockwool Coverrock II, followed by a base coat, reinforcing mesh, top coat, and facade paint.
About two weeks later, brown spots appeared in various places, irregularly distributed on all sides of the facade. There are small spots and larger spots up to about 10cm (4 inches) in diameter, some pale, some intense brown-red. Over the course of 2–3 weeks, more spots showed up, but now no new ones seem to be appearing.
Has anyone had experience with this?
An online search suggested it could be moisture penetration dissolving the binding agents and fillers, or phenolic resin residues, resin pockets in the mineral wool boards themselves somehow coming through.
During the facade work, there were a few brief rain showers, so it’s possible the mineral wool got wet.
However, against the moisture penetration theory is that some spots appeared directly under the eaves, places that couldn’t have been exposed to rain, or on areas that were only installed after the rain. Overall, we had a very favorable weather window for that time of year.
The very irregular appearance could support the phenolic resin residue or resin pocket explanation. As far as we can tell, it’s not related to the board edges or possible fixing points.
Has anyone observed this phenomenon before and how was it resolved?
Thank you very much
Here is finally a small update.
The theory that residual phenolic resin dissolves/fades/evaporates under UV light seems to be correct.
Many stains are no longer visible at all, a few are still faintly noticeable, but only the stain in the reveal and the one under the eaves remain clearly visible.
So far so good, our house apparently is growing out of its adolescence.
If you look very closely, you can see that the plaster in those areas has a different texture. You could describe it as small acne scars.
The theory that residual phenolic resin dissolves/fades/evaporates under UV light seems to be correct.
Many stains are no longer visible at all, a few are still faintly noticeable, but only the stain in the reveal and the one under the eaves remain clearly visible.
So far so good, our house apparently is growing out of its adolescence.
If you look very closely, you can see that the plaster in those areas has a different texture. You could describe it as small acne scars.