Very interesting subject. I have a 20 x 30 ft N scale layout that is all track and I have a lot more ballasting to do. But I do have some experience, so far.
Fine is the size you want for N scale. I used Arizona Rock and Mineral for the mainline. It was expensive (24 bags), so I looked for an alternative for the yards. I settled on ordinary concrete type sand you buy at Home Depot/Lowes. It is silica, and after you glue it down, you can still see through it in places. But, this is not the color you want, it is only the texture. I air brushed it and I think it looks very real. You can no longer see the grains after you airbrush; everything blends in. But, I was doing a yard and sidings so for me, the ties were buried with no discernable roadbed. It was the look that I liked. The soil was painted a yellow clieche (sp..also called mud by some) color to match the San Antonio area soils.
This sand had to be sifted to achieve consistent granular size. I came up with coarse, medium, and fine and achieved this by filtering through paint filters made for those professional high pressure sprayers. Each filter is a cloth like and there are many sizes. Some for spraying stucco (very coarse) and others for spraying final touches on fine furniture. All are available at the hardware store.
I found no magnetic particles in this product. It was mostly silica, so maybe that is why.
Finally, I will add that this worked for N scale. I have a little HO experience, and the different scale size causes detail to be more critical in the larger scale. That is obvious when working on a model engine or rollingstock, but it is also true when making leaves, bushes, apples, weeds, etc.
I don't have a picture to post here, but you can see a picture of my layout and the yard ballasting in the latest N Scale Railroading magazine. About page 34, I think. I have the tiff photo of that here. Maybe I can convert it to a jpeg and post it. Would that work or would it still be too big?
Once again, this is a subject close to my heart.
