Surface not optimal

I use the sheet size 100X150 at school. After installation, I could pull off the foil clean, but I was disappointed with the quality of the panel. It is not smooth and shiny (like I knew esbisher with smaller tablets), but rather rough and matt. I use three different brands of whiteboard Stifen and a quality wiper with changing towels, but really it is not possible to clean the board. Only when I wiped wet and intensively with a microfibre cloth, the table was really clean.
Unfortunately, it's too late to exchange them, since I had to rebuild.
90 which would have created bad sind.Ich me a more detailed description required here.