To lay the first course, apply a thick bed of mortar using the horizontal guide and trowel. Depending on surface unevenness, consider placing only the first two courses and let the project set up overnight before continuing. Place the horizontal guide on the course and slide it along the wall, scraping mortar into the channel as you proceed. Do not get ahead of yourself or the mortar will set up too quickly. Pace yourself and give yourself enough time to comfortably install the bricks into the bed of mortar.