Hi ginkob,
Welcome to The PainterFactory!
I'm not sure what you mean by "watcolour vendor", but I believe squirrel is referring to the Corel Painter Digital Watercolor brush category which is available in the following Corel Painter versions:
Painter 8 through 8.1
Painter IX thorugh IX.5
Painter X through X.1
squirrel and ginkob,
It's not necessary to add texture before painting unless you want to. Any brush variant that interacts with Paper texture will apply the appearance of texture in the brush stroke as you paint.
Also, as long as Digital Watercolor paint remains wet, the Wet Fringe slider can be adjusted to control how much the wet fringe shows.

In the demo below, you'll see two Papers each set to three different Papers palette Contrast slider settings, and again using the Painter X.1 Digital Watercolor's New Simple Water variant:
