ᐅ Mold Behind Baseboards – Any Experiences?

Hi, I recently removed two baseboards from exterior walls for a different reason. Could this be mold? On one baseboard, there are black marks that might also just be fingerprints. On the second baseboard, it looks similar to dirt, which could also possibly be animal droppings.

The baseboards themselves and the wall behind them are not damp, I measured this. Could there still be too much moisture in the screed? I installed the floor myself in a new build about 15 weeks after the screed was laid, with some technical drying, but I didn’t measure moisture! It was a 7cm (3 inches) flowing screed. The wall is made of thermal pumice blocks without additional insulation. The temperature inside the house is around 23°C (73°F) everywhere with 30 percent humidity. I sealed the top of the baseboards to the wall with acrylic.

Back to the baseboard – I reattached it without any treatment. Now I’m wondering – if it was mold, should I remove all baseboards? What do you think? And if so, only on exterior walls or really all of them?

I’m attaching two photos of each baseboard.

Thanks and regards,
Julian

It looks rather harmless. Yes, the damage could be caused by moisture release from the screed. It doesn’t dry out evenly. Possibly just remove the baseboards and reinstall them.

Hi, thanks for your reply.

How would you proceed specifically?

Remove all the trim right away? Only remove the exterior wall trim? And once removed, treat with mold remover, let it dry, and then put it back? Leaving it off permanently is not an option because of babies. That would only be possible for a maximum of 24 hours.

Or, based on the photos, do nothing for now and perhaps check behind other trim strips in the summer?

Thanks and best regards

This appears to be a rather minor infestation—more like early-stage mold spots. It likely occurred shortly after the baseboards were installed and the remaining moisture evaporated. How long have the baseboards been mounted? Further progression of the infestation requires continuous moisture exposure. As a test, I would remove baseboards in 2-3 rooms, preferably on exterior walls, and check the condition there. If it looks similar, I wouldn’t worry further and would reinstall the baseboards after a few days. It is currently the heating season, and especially the first one after construction and completion of the house brings many special conditions. For example, we have noticed condensation issues at exterior electrical boxes, the front door, attic stairs, windows, roller shutter cable entries, and so on. This needs to be addressed and then monitored.

The trims have been installed since, I would say, August/September. We’ve been living here since October, and the heating has been on since then. So, roughly four months, I would say.

At the moment, I’m leaning towards completely removing the exterior wall trims in the coming weeks, or towards the end of the heating season, to clean them, let them dry, and then reinstall them. From your responses, I gather there isn’t any urgent need to do this right away.

Maybe I’ll also take the opportunity to check behind an interior wall! Does that sound like a reasonably sensible plan?

I wouldn’t wait to remove it on a trial basis. Do it right away so you can see if any further urgent action is needed.

However, I think it has dried by now and you will only find traces from last summer.