When extending an existing ceramic tile floor into an addition, it is important to keep the grout lines straight and in line. Don’t trust your eye. You won’t be able to keep these lines straight by just eyeballing them. You have to create guidelines to follow.

One method is to use a regular chalk line to make your lines. Place a loose tile on the existing tile floor and wrap the chalk line around the tile, hooking the line to the underside of the tile. Pull the string tight and line the string up with the edge of an existing tile. Run the string down to the end of the existing tile floor and first check to see if the original tiles are in line. If so, you are in luck. Make a mark on the concrete floor just beyond the existing tile and directly under the chalk line.

Then extend the chalk line all the way to the end of the room and line it up with the existing grout line and the mark you made. Mark the location of the string when it is all set. Then place a heavy object on the string to hold it in place. Make additional marks under the string at several locations.

Then using a level or straight edge, draw your line along those marks. By drawing the line with a pencil, you are a thinner, crisper line. This is easier to follow then a chalk line. Plus it will not be erased as easily as a chalk line.