Archviz - using decal for floor smudges gives black spots


I’m trying to add smudges to wooden floor. Enabled dBuffer decals, works kinda fine for color decal as you see on bottom of walls (although it gets washed too much under light, but that’s for another thread). Floor decal is problematic. When I plug black-white texture to roughness node, floor is black white and rougness is working as should. What you see below, is a result of smudge texture connected to decal’s roughness AND opacity. I don’t know why a decal that’s set to translucent mode, still gives black-white color overlay over wood texture.