I love the black diamond sand. We are fairly new to tanks and in the last 6 months we have gone trial and error on the caps I use. Finally have settled with black diamond 30/60 and it's beautiful! I have it capped over soil and over ecocomplete/floramax in some tanks. So far have had no issues. I took my time and spent a good bit of time washing it until the layer of water washing it with had absolutely no floaters and no sign of any residue on the water surface. The fish, especially my cories love it.
We tried aquarium gravel, pea gravel, pool filter sand, quickcrete sand and regular creme colored aquarium sand. Prefer the black diamond over all of this.
On topic- your soil will start to stick together after it is aged and the gunk from your tank gets into it to seal it together. The first few months are kind of messy if you move things around but after that it shouldn't be an issue.
We did put the plastic mesh craft cloth as a liner around the edges of the tank above the soil - we had a large pleco who liked to get in the corner of the tank and swish his tail back and forth in the substrate, after waking up to brown muddy stirred up water a few times, we had to cage the soil off around the edges of the tank so it wouldn't happen again.