Poroton brick interior wall has black spots - mold / fire?

I have little experience with modern bricks in everyday life, but the "normal" bricks that I regularly handle also have different colors. This was even more pronounced with the historical stones. Otherwise, look for specialist consultants from Wienerberger and write them an email or call them. I think they are also interested in making sure a customer is satisfied. In case of defective material, they would also have to bear liability. You can find the contacts based on your postal code under Fachberatersuche at Wienerberger. I have also already called specialist consultants from other areas, and none of them have been dismissive.

Thank you very much for your answers.

In the last few days, there has been a lot of sun and dryness, and it doesn’t look so bad anymore. More gray than black. There is also no fur or bloom on it that could be scraped off.

I also spoke with a field representative from Wienerberger, without him having seen any pictures. He also confirmed to me that there is no mold on the Poroton, neither from firing, storage, nor delivery on the shrink-wrapped pallet. Even if the pallets have been lying somewhere for a while. He said it sounds like burn marks, which apparently happen occasionally. However, the spots are said not to affect the bricks regarding usability or the adhesion of plaster, etc.

My note: I assume that a Poroton brick would also get mold if, for example, it is installed in a permanently damp environment, but that is not the case here; the bricks came "fresh" from the pallet.

Regardless, the site manager also said that these should be harmless burn marks but has commissioned Wienerberger to send someone to the construction site to take a look on-site.

Regardless, the construction manager also thought that these must be harmless scorch marks but commissioned Wienerberger to send someone to the construction site to take a look at it on-site.

That is good. Visually, the phenomenon reminds me of mold stains or freezer burn, but those are more or less creative associations rather than diagnoses ...

As fate would have it, we received mail today directly from Wienerberger with a statement.

I will copy the generally relevant part here:

"...Poroton bricks are coarse ceramic natural products, in which surface variations in the form of discolorations due to manufacturing cannot be ruled out despite the most modern production technology. For this reason, normative requirements regarding coloration and surface properties of back-wall bricks are not included in any technical regulation.

The detected discolorations in the form of dark spots on the brick surfaces are so-called reduction phenomena, which are due to short-term fluctuations in oxygen supply during the firing of the bricks. The resulting partial darkening of the brick material represents solely a visual, insignificant impact on later plastered masonry. The detected discolorations have no effect on the building physics properties of the masonry.

An irreversible chemical-physical material bond has been formed in the bricks through the firing process, which, for example, cannot be dissolved again by the influence of moisture.

For the reasons stated above, bleeding-through of the reduction spots through the plaster is by no means to be feared, and the plastering can be carried out according to the manufacturer’s recommendations as well as the generally recognized rules of construction technology.

The delivered brick material corresponds, for the reasons stated above, despite the detected color differences, to the required product properties and quality criteria and is to be considered a standard safe plaster substrate when processed correctly.

Compliance with the building physics properties of the masonry, such as thermal protection and load-bearing capacity, is ensured in any case when complying with the processing guidelines from the general building authority approval or DIN EN 1996.

We are happy to Besta confirm that the delivered bricks correspond to the contractually assured quality properties.
..."

So all good! :)

Not that an average builder would be able to verify that...