I think 1/4 inch is to large. My main goal is to remove the powder and the very small pieces.

I use 1/8" mesh.  A lot still goes through, but it's a more reasonable yield per bag.

Mike

I use 1/8 as well and you still lose close to 50%.  

So I screened 2 X 20 gallon tubs of mulch (thanks for the tip Calvin) through a 1/8th inch screen.  

  

The tub on the left (screened twice )and center (screened once) were full when I started.  The bin on the right contains what passed through the screen.  It is just about half full or 25% of the what I started with.  The mulch was still damp from the rain we had last week.  I was able to get about 20% more out of the second pass than the first.  

About 3-4 cups of dirt per cubic feet washes out of the expanded shale I use.  I'll see how much fine particle passes tomorrow.  I went with the Pahrock perlite this year, so I should have less pass through.