Gutter pieces are often sold in long enough stretches to run across the entire length of your house, but if the gutters aren't long enough, or if you need to insert corner pieces, you'll need to know how to seam gutters together. Gutters are only useful if they are watertight, so there is more to the process than just screwing two pieces together. A special flexible aluminium piece, called a "seamer," is used between two gutter sections to bring them together.
Position the two pieces of gutter next to each other so they are about 1/4-inch apart.
Place the lip on the flat side of the seamer over the back of the gutter pieces. The middle of the seamer should be directly behind the gap between the two pieces.
Wrap the seamer under the gutter pieces, and lift the front lip of the seamer over the front lip of the gutter, so that it hooks on.
Crimp both lips of the seamer with the pliers, so that the seamer cannot come off.
Apply sealant to the seamer on the inside of the gutter. Place the sealant between the seamer and the underside of each of the gutter pieces. Use plenty of sealant to make sure that gutter is watertight.
Wait two days, then pour water from a hose down the gutter. Check the area with the seamer for leaks, and apply more sealant if necessary.