Indoor faux brick wall, can it be varnished or have a coat of poly put on it. The

[professor grey]

grout is a mud brown and the? brick is very dull looking. It only goes as high as the chair rail. My son wants to keep it, I just think it looks dull and dirty. Last night I tries to wash it and I liked how the water brightened it up. I was thinking if I put a coating on it it would stay looking clean and bright. What do you think? Can it be done?