We have hardwood floors in our nyc apartment. A friend did our floors. He did a deep scrub with Murphy Oil soap and scrubbed with steel wool on scratched areas. Then he applied two coats of bona floor poly satin per the bottle instructions. It looked really nice until some snow sludge dried on it. It wouldn't wash off without scrubbing off the finish.

Did we apply the poly wrong or is there a better product? Seems like the snow and salt should be easily washed off the surface without getting etched into the finish and needing to scrub it off. I can see this happening after an entire winter of snow and salt being tracked in but this happened immediately.

Your problem; No inner coat abrasion. Here's an example of the proper procedure. http://youtu.be/0FFEl0Y1MvI