I found black spots under the old wallpaper in my bedroom. I scraped them off, but I'm not sure if I got rid of the problem completely. What products should I use and do I need special primer before putting up new wallpaper?
I found the same thing at home in the bathroom - just stripped off the wallpaper and there's black mold all over the wall. Turns out just scraping it off isn't enough, you actually need to kill the fungus chemically.
Use an antifungal solution - usually it's either bleach diluted with water (roughly 1 to 10), or special antifungal primers like Finesta, Bioprina or similar ones. Apply it in several coats, let it dry properly between layers. The key thing is to wait for the wall to dry completely, which can take a day or two depending on humidity.
After that, apply regular wallpaper primer - it'll work much better on a clean and treated surface. And honestly, figure out where the moisture is coming from: why is there moisture in the bedroom in the first place? If it's from frost, poor ventilation, or a problem in the bathroom next door - the mold will come back no matter what products you use.
Is the wall damp, or were the wallpapers just up without ventilation? This matters because if high humidity is the culprit, the mold will come back even after treatment.
Scraping is only half the battle. You need to treat the wall with a fungicide (ready-made sprays like diluted bleach work, or special products like Snizhki). Let the surface dry thoroughly, then go over it with an antiseptic primer - it creates a protective layer and prevents mold from spreading under the new wallpaper. Before you hang new wallpaper, make sure the wall is completely dry and the room has good ventilation, or you'll end up with the same problem again.
if you just scraped it and called it done - unfortunately, that won't work, the fungus lives deep in the wall and will come back under the new wallpaper. you need to treat the surface with an antifungal, i used regular copper sulfate solution or bleach (diluted roughly 1:1 with water), and let it dry thoroughly for about 3-4 hours. after that, you absolutely need to prime it with an antimicrobial primer - it'll stop the fungus from spreading further, plus the wallpaper will stick better. the main thing is figure out where the moisture is coming from, otherwise it'll all happen again in a year.
The main thing is not to forget about what's causing the mold, or it'll come back. If the wall was just covered with wallpaper without proper air circulation, scraping it off plus treating it with an antifungal should do the trick. But if there's actual moisture (condensation, leaks, poor ventilation in the bedroom), you need to deal with that first - improve ventilation, check the seals, maybe even put in a dehumidifier.
As for products: after scraping, wipe the wall down with an antiseptic or fungicide (there are special formulas like Mileu, Biodep). You can use copper sulfate diluted - it's a tried-and-true option. The key thing is to soak not just the visible black spots, but the whole surrounding area too, because spores are everywhere. Let the wall dry completely - this can take a day or two.
Then use a primer with antifungal properties before putting up the wallpaper. This creates an extra barrier. And make sure to check that the air in the bedroom dries out properly - ventilate regularly, don't let moisture build up. Otherwise it'll all happen again.
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