I have a large area (walls) inside a house, that I would like to cover with polyurethane, and I was told that you can use a pump-up sprayer to apply polyurethane if you thinned it with paint thinner. Has anyone ever tried this before? Will this work?
Once you thin it so that it can come out of a garden sprayer, you will want to do as Joe said, and be there with a roller so that it lays right and gets even coverage. A roller would be easier, yet you will want to be careful not to cause air bubbles on you walls.