If your house has a drainage problem, you may have water that runs into the garage every time it rains. On many older homes, the garage floor was just a flat slab of concrete. Many new homes are now designed with foundation plans, that direct the concrete subcontractor on how the slab is to be sloped to provide adequate drainage. You can fix this problem, with a trench drain in the garage floor using tools rented from your local tool rental store.
Mark the location of where the trench is to be located. Snap a chalk line between the two marks on the floor. Carefully, measure from the chalk line the width that the trench needs to be at both ends. Mark the concrete with a pencil at the two points. Snap a second chalk line between the last two pencil marks. Use a pencil and chalk line to mark the concrete for the chalk reference line.
Put your safety equipment on. Concrete makes a lot of fine concrete dust that is dangerous to breath. Additionally the cut off concrete throws a lot of small pieces of concrete debris as you cut.
Place a 1 by 6 piece of wood next to the chalk line. The lumber will serve as a straight-edge guide to score the concrete. Start the cut off concrete saw and score a line 1/4-inch deep next to the lumber. Walk on the 1 by 6 as you score the concrete to keep the guide from moving. Move the board as needed until you have scored all of your chalk lines.
Cut the rest of the way through the concrete using the score lines to keep the cut straight. The cut off saw has a diamond tipped saw blade. This blade is designed to cut at high speeds with light pressure. Let the saw do the work, and do not try to force the blade faster into the concrete. This will only cause the expensive diamond blade to dull quickly.
Use a 4-inch grinder with a diamond blade to cut in confined spaces. Score the concrete that is to be removed 1-inch deep in several places. This causes the concrete to break along the score line when hit with a sledge hammer. Using this method will help remove the old concrete a lot easier task.