Mold Infestation Carport Karibu - Classic

A few boards of my tongue and groove looked like this. The seller had stored them outside under a tarp and where the water stood, the boards looked like this. I treated them with hydrogen peroxide and then let them dry indoors for a while. After weeks, nothing spread, so now I moved them to the attic. I have no problem using them now... But tongue and groove is not pressure treated and I fear that the boards in your picture aren’t either.

Good point. The post has nothing, the board right next to it does

Yes, it rather looks like no boiler pressure impregnation took place.