The key to painting concrete is to first clean the surface so it is better able to hold on to the paint. To make stripes in a set of concrete steps and mark the edges for utility, safety or decoration, use a paint specially formulated for painting stripes on concrete, like that which is used to paint stripes and dividing lines on roadways. The paint will last a long time on your steps and it won't run beneath the tape used to mark them off, so the stripes will have straight edges.
Prepare the surface of the concrete steps to receive the paint. Scrub the steps with a solution of trisodium phosphate mixed with water, following label directions. For any extra-greasy spots, put down a 1/2-inch layer of kitty litter. Let the kitty litter soak up the grease for a few hours. Sweep up the kitty litter and then scrub the area with the trisodium phosphate solution. Rinse the steps with clean water and allow them to dry thoroughly for several hours.
Use extra-sticky masking tape or duct tape to mark off the stripes. If necessary, measure with a ruler to achieve the striped effect you desire.
Paint the stripes after you have laid out all of the stripes and taped them off. Use an extra-fluffy roller and apply a thick coat of paint specially formulated for striping concrete or asphalt roadways. This paint is thicker than regular all-purpose paint, so it will not run into the pores beneath the tape, in the irregular surface of the concrete.
Remove the tape when the paint is still wet. If you wait until the paint dries, it is possible that the dry paint will stick to the tape and remove chips of it along with the tape, giving you stripes with irregular edges.
Seal the stripes, if desired, with clear sealer. The sealing top coat will keep the stripes looking new longer.