for my magnetic board I've used a sheepskin paint roller. ATTENTION The color is first vigorously stir up the bottom, there is the iron settles. Then I gave it in portions in a tray for paint roller.
The resulting layers were sufficiently thick. After the first layer held a 0.5 cm Neodymwürfel on the wall but only after the third was the color homogeneous and not stained.
The color has far exceeded my expectations. The consumption of 1L to 1.7 m² with three paintings, I can confirm.