How can I safely clean and repair the moisture-damaged wood around my north-facing bathroom window to combat mold without any rotting?
Asked by Sandhia Van Hooff 
2 months ago
Last Updated: July 26, 2024
Any ideas on how to fix the wood around this window? It’s facing north, so it’s probably a moisture problem. The wood looks fine, but I’m guessing it’s mold. It’s in a bathroom. I’ve already put in a better fan, and the windows are 10 years old. This has been a problem from the start. Any suggestions on cleaning and fixing/sealing it up if possible (no rotting)? Thanks!
Chances are it’s a water stain. You could try sanding it down to remove it and then restain the area.
It might actually be mold, but replacing it could lead to better results with less effort.
It might not actually be mold. Some suggest it could be staining instead. If it is staining, sanding might help soften it, but it may not completely remove it if it’s severe.
Why is my wood turning black?
There could be two reasons why wood turns black. It might be because of mold, or a chemical reaction between tannins in the wood and minerals in the water. To fix this, you’ll need to strip and bleach the wood or replace the affected boards with new ones.
I can’t say for sure, but I managed to remove the tannin stains. However, they reappeared after leaving the wood exposed to the air for too long after stripping. I believe they wouldn’t have turned dark again if I had sealed it sooner after cleaning and sanding.
I wanted to express my gratitude for your advice.
I have a visual example to show you how it looked. As I mentioned, those stains were almost completely gone before I had to leave it to sit for about a week. (My life is full of interruptions, so this happens with almost every project I work on, with stops and starts)
Regarding the staining, you could attempt bleaching it with hydrogen peroxide, UV light, or a small amount of bleach. It’s worth a try as a last resort, but test it on a small piece first to see the outcome.
The staining is likely a result of decay. The extent of repairs needed will depend on how severe the damage is. First, you’ll need to address the water intrusion problem. If it’s been an issue for ten years, there may be significant damage hidden in the wall.
Try using Concrobium Mold Killer. Thrasher basement crew recommends it because it doesn’t stir up mold spores like bleach does before killing them off.
If you find a leak in the window, make sure to seal it before replacing the window.
If it’s a stain and not related to mold or decay, consider using oxalic acid. If it is mold or decay, remove all the trim and woodwork to check behind it. You may need to take out the window for a proper inspection and repair any damage.
First, use Killz stain blocker before painting.