I am trying to add this rust texture that I found over my brick texture cube. The rust is transparent, and i am selecting a specific area of the cube to have the rust over. I separated the specific faces i wanted the rust on by material, and i added the rust image texture, then plugged it to the roughness node. All that appears is a white square. I tried to texture paint but it doesn't give me the result i want. I followed other tutorials where it said to put both the image textures for (in this case brick and rust) through a mixRGB node, but then the rust appears everywhere on the cube. I tried a different method, this time doing what i mentioned again but in it's own material, (separating the faces, giving it its own material, then adding two images textures, brick and rust, then going through the mixRGB node) which did a bit better, but the brick texture was being stretched whenever i tried to adjust the image in the UV editor. What other solutions are there that i can try out?
(I got the idea of putting the rust on the roughness node from Blender Guru's video on making a subway in 20 mins, but i did not get the same results. The Color Ramp did not change much for me.)