1. Open Photoshop. Open an image to apply patchwork grid effect.

2. Create a new layer in the layer palette and fill it with white color. Keep the layer selected.
3. Filter > Texture > Patchwork
Square Size – 1 Relief – 0

4. Change the layer blending mode to Color Burn and Opacity to 70%

Source : http://www.tutorialguide.net/patchwork_grids_tutorial.html

