ᐅ Poroton brick interior wall has black spots – mold or soot?

Hello everyone,

We are currently building a single-family house using Wienerberger Poroton blocks.
All exterior walls and the interior walls on the ground floor are fine.
However, all interior walls in the attic level show black spots.

These are non-load-bearing walls, 11.5cm (5 inches) thick, made of unfilled Poroton bricks.
(To be precise, Wienerberger Poroton high-porosity hollow bricks, Plan-T, 11.5cm (5 inches) thick with a bulk density of 1.2.)

Since there has been a lot of rain and storms over the past weeks, I was concerned that the bricks might have absorbed too much moisture and started to mold.

I only noticed this now (March 1, 2022), after the roof structure was installed. The roof is about to be covered, and I fear it might soon be too late to fix anything, apply anti-mold treatment, or rebuild the walls.

Unfortunately, I have no idea whether this is necessary at all. Is this mold, or manufacturing-related scorch marks or similar?

I can’t find anyone who can tell me whether this is okay or if it is a defect.
I also found a photo from the end of January, when the interior walls were being erected. Even then, there were black spots on the wall and on the bricks stacked on the pallet.

The bricks were delivered directly on pallets, lifted with a crane onto the attic floor, and built in within the following days. So it seems very unlikely that this is caused by excessive rain.

Is anyone familiar with this issue of spots on Poroton bricks?

Thanks in advance for your advice!

Best regards,
Daniel

Hmm, that really looks strange. I don’t think it’s mold. Mold usually spreads differently, but I could be wrong.
What does the construction manager or the structural builder say about it? Do you have a building inspector?
Maybe the pallets were stored in a dusty environment for a long time.
Sorry I can’t help more. Maybe:
@jcan or @Jann St know more about this?
Or has @11ant seen something like this before?

Tolentino schrieb:

Hmm, that really looks strange. I don’t think it’s mold. Mold usually spreads in a different way, but I could be wrong. [...] Or has @11ant seen something like this before?

No, other than agreeing with the beginning of your post, I don’t really have anything to add here (which is why I haven’t said anything so far, although I’m online right now). Let’s just hope it helps that you’ve already called in professionals.

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@herrfield .. in such unusual situations, a brief feedback would be very helpful for other forum users.

I would rule out mold. I think it is most likely discoloration from burning. So, very likely nothing that will cause you any problems.

jcan schrieb:

I think it’s probably discoloration from firing.
So most likely nothing that will cause you any problems.

Yes, “problems” might be too strong a word here, but I would not consider such color defects chemically significant (?)

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