My routed track is painted with a material called Plasti Dip. Put on with a disposable foam roller. Great grip, races clean, stays clean, tough as nails.
David in Spain used a material called "Clorobarp" I think it is made by Barpimo, a walk on rubber coating, he loves his surface as well.
I would encourage you to never use abrasive or sawdust etc. Abrasive will grip, it will grip the finish on the top of your car during a crash too.
Sawdust will sluff off on the tires, creating a very slick condition.
here in the states, most tracks are painted with latex. Most love them, some have repainted and repainted to try and get a surface that doesnt slick up during racing and provides good grip. I read all I could find and I found Myron in Oklahoma who was not happy with his first track painted in latex. He did the experimenting and discovered Plasti Dip. Boy am I ever glad he did.
There are threads on homeracingworld, www.auslot.com as well covering this topic. Recently several tracks in Oz got overcoated with plasti dip and they love it.
Here is a picture of my track, I mixed black and white in the rolling pan, they dont make a grey.
Plasti Dip here is about 65 dollars per gallon, but very expensive in europe and Oz. Surely some other rubber coating is available that could do the same thing.
enjoy your project.
John