Elmer's Glue-All white glue, or Mod Podge Matte Medium (NOT Gloss), would work just fine. Mix approx. 15% glue with 85% tap water, with a few drops of dishwashing detergent, in a quart spray bottle for applying. Carefully mist it on over your dirt. You can simply lay old newspapers down to protect areas or items that you don't want sprayed. These glues are white when wet, but will dry clear and flat.What works best for securing dirt or coffee grounds to plywood for authentic scenery. Clear guess not the best results?
No, full strength anything doesn't work to well. Except to establish a base coat, as I indicated. To Mixed Freight's point: mediums (Mod Podge, Liquitex, etc.) are what artists use to adjust the consistency of acrylic pigments. They come in several "flavors": gloss, satin, and matte, typically. Matte simply means "flat" or not glossy. They're meant to be resistant to wear, fading, and discoloration, as well as somewhat flexible. They are more expensive than glue, but they last longer. And the dilute alcohol mixture will soften them and allow them to be scraped off.Thank you so much for your excellent ideas. I meant to say white glue didnt work too well. I'll give it a try and see what happens.
I also use aliphatic resin (yellow carpenter's glue) for 90% of all my roadbed and scenery, including ballast and dirt. I'll spray it diluted, or use it full strength, depending on the application. It doesn't show up anywhere as shiny stuff in the scenery, or in the ballast.I used yellow wood glue diluted with 2X times as much water and thoroughly mixied, then brushed on first.