Right-click and select fill paths. Fill it with #C9C9C9. Then choose Filters > Noise > Add Noise. Choose something around 9.51 (just enough to make it look more realistic and lose it's hardness) in the monochromatic and uniform setting. Press the 'Escape' button twice to remove the path. Draw the brush strokes as shown and then go to filters > Blur > Gaussian blur > 2.8 pixels.