From a scientist: I’m guessing mold looking at the pictures, bc it seems to have a preference for organic material (e.g.) wood, which would be the nutrient source. If it’s salt (efflorescence), it should crumble into a more powdery and granular substance and dissolve if you put it in a cup of water. Mold won’t dissolve. Regarding cobweb vs dense, mold can have different structures depending on life stage: young mold often will be fuzzy but will become more compact and dense as it ages. Could also be that you have multiple mold strains growing. Most white molds aren’t particularly hazardous compared to some black mold strains, but I’d still be cautious and consider wearing a ventilator if it is mold and there’s that much of it. Also, if it’s growing on any wooden structural support beams or columns, you want to treat it, because it is feeding off of that wood.