- Create a new layer above your text layer.
- Place your grid element on this new layer.
- Create a clipping mask with the layer that has your grid element.(In Photoshop, you right click on the layer and select "Create Clipping Mask")
- Re-position your grid element so it is on top of your text!
You can find more information on this technique by searching for how to create a clipping mask or masks in your graphic application of choice.