Working with powdery soils is difficult from the standpoint of getting a flat, smooth surface, free of ridges, bumps, and craters.  There are two challenges.  First is applying the material smoothly.  Second is applying the adhesive without disrupting your application.

To get a smooth application, avoid pouring the material from a cup.  Instead, use a fine meshed sifter.  Pour your material into the sifter and lightly bounce it up and down and swing it side to side until you’ve covered your entire surface area.  If additional smoothing or dress up is needed use large, soft, flat brushes.

Next comes applying the adhesive.  I prefer dilute matte medium from Scenic Express.  Pick up a spray bottle that produces a super fine, gentle, mist.  Fill it with a water and add a touch of rubbing alcohol or detergent to aid in breaking up the surface tension.  Spray your soil base that so that it’s saturated but not puddling.  I use an eye dropper to apply the matte medium.  If you’re not careful applying the drops, you’ll end up with unsightly ridges or craters.  Start at the edge of your soil area and liberally apply the adhesive around the edges.  Wait a moment and let the capillary action draw it into the soil as far as possible.  To hit the remaining dry areas, hold the dropper just a hair above the surface and very gently squeeze out a drop.  Again, see how far the capillary action carries it.  Repeat until the entire surface is saturated.  If you end up with any ridges or bumps lightly smooth them out with a flat, smooth, brush.