Help identifying possible mold and remedies for it

7 years ago

I repaired what I thought were long scratches to the baseboard in a small room (containing just the toilet) in a bathroom. I sanded, filled, sanded again and when fully dry, painted. Two weeks later the same marks are back--and in the same place. This makes me think this is something organic like mold, although it seems odd that it's in the exact same spot. (Not that I want it to spread!) I have also noticed 'drain flies' in the room, which supports a theory of it being damp somewhere.

The walls on either side and behind the water closet look normal both in the room and outside/around it. The bathroom is over the slab but the basement ceiling right next to the slab area also appears normal, no sign of water.

My questions are: Can anyone identify this? Do I call a plumber or a carpenter?

Thanks for any help!

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Comments (7)

User
7 years ago
Looks like resin bleed to me. As in, was the molding pine, and not primed with a shellac based primer?
klem1
7 years ago
I'm thinking along same lines as S Wheeler. If not resin,maybe fungi growth. Either of those involve a crack,examine carefully next time you repaint. I don't know what it is but it doesn't look like any mold I've ever seen. In a nutshell,it would rank pretty low on my list of things that need worrying about.
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olive51
Original Author
7 years ago
Thank you for your responses. The resin bleed makes sense, as I now realize that I didn't use primer! Maybe a product like Kilz would be best? I'm pretty sure the base is MDF (other base in the house definitely is). Would MDF have a resin bleed? I could start over and use primer this time and if it comes back I can consider the fungi angle. Thanks again!
User
7 years ago
What filler did you use?

Resin bleed comes from pine or similar woods, not from MDF. I agree that does not look like mold/mildew.

Kilz is fine as long as it is the shellac based type---the shellac base is the active resin/etc. block. Water based Kilz is a stain(mainly water stain) blocker. My personal go to shellac primer is BIN(by Zinsser). Mainly because it is thinner than Kilz. A surface prepared for BIN has to be smoother and blemish free, however, since the BIN does not cover/fill scratches.
olive51
Original Author
7 years ago
I've done some research and can't find anything about resin coming through MDF, as you point out. Maybe the base is regular wood, which makes sense seeing how whatever this is is in streaks that could indicate wood grain. I also found top marks for Zinsser BIN, so your advice is quite sound, thanks! I used 3M Patch Plus Primer spackling compound, sanding before and after.

I plan to start over using the BIN this time.
klem1
7 years ago
I'm surprised that after sanding on it you don't know for certain if base is wood or mdf. Now that everyone agree's it's not a health threat ,why not carefully slide a razor underneath and lift some off? That would allow seeing reverse side that isn't coated in paint. Resin is tacky and consistency similar cold caramel candy. Fungi is often similar to spray foam insulation.
olive51
Original Author
7 years ago
Haha, I agree, you'd think I would know if it was wood or MDF, but in my meager defense, I just did a bit of sanding and the base is about 8 inches from the side of the toilet toward the back and not easy to get to or even see clearly.

I'm now nearly certain this is wood with resin bleed-through. I scraped some off, it was caramel colored and dry and powdery, but where I took it from did feel a bit sticky. Thanks to everyone who took the time to help me solve this puzzle, I really do appreciate it!