Did you know that you can be just as creative with using marking making tools, with water colour paint, as you can be with using acrylic or oil paint. During this video Liddy uses corrugated cardboard to create a range of marks. (video has no sound)
Cut the corrugated cardboard to the desired length/size/shape.
cover the edge in paint make sure the paint isn't too wet- there needs to be a strengh of colour/pigment to the mix as it will make a much better print of the corrugated pattern.
Depending on what you want to add texture to or use the corrugated card board for- explore the range of marks you make. For example: a controlled and linear application of the cardboard on to your page/painting will achieve straight and structured lines- great for creating a brick like texture in architecture. If you add a little bit of a wave or a wobble when pressing down the cardboard and move it around you can create a texture better suited to water or the sea.
In the video Liddy uses the edge of the cut piece of corrugated cardboard but you could try using the flat surface and you could even peel away the top layer to expose the ridges underneath and use those.
Have fun and explore the range of marks you can achieve, only by experimenting will you discover new and exciting ways to paint and work. When you're experimenting with the cardboard try to match those marks to things you might see everyday (trees, bark, bricks, buildings, water, reflections, etc) This is a great way to add those tricky little details and textures into your painting without having to use a paintbrush.