Vallejo Matte Acrylic Varnish is the same medium as Vallejo Premium Varnish Spray, just in liquid form. It therefore allows for precise application.
Like its "spray sibling," Vallejo Matte Acrylic Varnish works excellently as an adhesive and dries to a matte finish without leaving any residue.
For instructions on using Vallejo Acrylic Varnish and further fine-scale ground detailing with flock, please see YouTube:
„Special Rund ums Gleis Teil 3: Gräser und Unkraut 
