Two-handed Hammer
The sledge hammer requires two hands. Because of the extra arm and hand strength, these hammers can range up to 20 pounds. Most often, they are raised over the head and then dropped (while still holding on to the handle) so that the force of the weight will drive a post into the ground, break concrete or drive a wedge. Extra force can be applied by swinging the sledge hammer downward (instead of the dropping motion) and squatting slightly to increase the velocity of the hammer.
One-handed Hammer
The heaviest one-handed hammer is the lump hammer. This hammer consists of hardened carbon steel and is used to make the strongest one-handed blow possible. These hammers can weigh up to four pounds.
Wielding a Lump Hammer
Because of the potentially dangerous blow a lump hammer can deliver, it usually has a very short handle. This allows the person wielding it to control the direction of the blow. That control must also be exerted on the bounce-back after the blow to make sure the hammer doesn't veer toward the worker.
Chiseling with a Lump Hammer
A lump hammer is often used for chiseling. The extra-heavy head can drive a chisel through many types of tough materials. For lighter blows during chiseling, grab the hammer's handle closer to the head. This reduces the force and increases control.