I am in the process of applying polyurethane varnish to a finished workpiece and have been sanding between coats as advised by the manufacturer instructions.
I initially wondered why this was necessary until, after applying the first coat, I noticed that the wood was bumpy where it hadn't been previously. Why does this happen?
Am I doing something wrong? My assumption is that sanding between coats ruins the finish.
I used this varnish: http://www.woodoc.com/products/24.