Chalk it up to Experience
One of the handiest things a roofer can have in his toolbox is a chalk line. Reliable for creating straight lines to follow when installing composite roofing tiles, a chalk line is basically a taut nylon or string that is coated with a loose dye, usually chalk.
As roofers know, pulling the string tight and then plucking it sharply leaves behind a chalk marking … and this line is followed for installing slate roof shingles and composite shake tiles. While this is one of the easiest-to-use tools available for a roofer, there are still some "tricks of the trade" you need to know.
First, be careful of the material in your chalk line and try to use just chalk — not a "permanent chalk" or a colored chalk that will be difficult to remove (especially red as it will permanently stain the tiles). Stick with a washable blue chalk that won't cause a permanent marking. (See Using the Right Color Chalk Line)
Second, if you're running a chalk line on a very long expanse, consider a "double snap" procedure. This is where the chalk line is pulled across the long area, then held down in the center by a second person or staple. To the left of the center area snap the line, then do the same thing to the right of the center area. This "double snap" gives a more precise line over a long area.
Third, have a back up chalk line in your tool box. Nothing is worse than getting to the job site and starting to mark the roof and having a brittle string break from overuse or tension on the line. This can mean stopping work and going to the local hardware store for a replacement chalk line. It's faster to keep a spare in your tool box.
Fourth, with DaVinci tiles never place a chalk line on the tiles themselves. After determining where the butts of the tile will be place a chalk 18” above that point and make a line. Use that line on the underlayment to align the top tips of the DaVinci tiles.