Pour the paint from your paint can into a large plastic bucket. This prevents overflow as you mix in the grit additive.
Measure 1 pint of grit for every gallon of paint you use. You can increase the amount to 1 quart of grit per gallon, depending on how you want the surface to feel underfoot. More grit results in a rougher surface.
Mix in the grit additive. Stir using a wooden dowel until the grit is thoroughly mixed.
Paint the surface immediately, or pour the grit and paint mixture into airtight containers if you plan to paint later. Mix the grit and paint mixture occasionally as you paint to prevent the grit from settling into the bottom of the bucket.