I was trying to clean my garage, which is attached and has a garage door. It is about 40 years old. There was a lot of dust on the fire blocks, so I was using a brush to brush it off. Then I noticed I could brush the walls- which are unfinished wood- between the studs and a lot of dust came off of them - so much that I had to use one of those OSHA masks and goggles. What is this stuff? The outside of the garage is an oil-based stain. After brushing, the walls seem lighter in color. It has basically had no maintenance. What do I do now? There is a can of wood preservative in the basement. Maybe it was used when the house was built.