make a patchy trans map, squars of white squares and black, put it on a layer node then ontop of it in the layer node attatch a ramp with, set the blending method to multiply on the layer node.

Make a sampler info node and attatch the facing ratio attribute to the v coord of the ramp. Edit the ramp so that it is transparent at the edges and solid in the centre. This should give the correct effect if im not mistaken, you want no interpolation between the gradient values.