Roof Mates' new Air Knife is a real knuckle saver. A cross between a pneumatic tool and a hook-blade utility knife, the Air Knife's reciprocating piston zips the 1-1/4-inch-deep hook through shingles in a blur with just a light draw force. It's great for trimming rake edges and valleys, and cutting into shingles or around vent stack boots as well as trimming starter shingles.

Action. Pulling through shingles with a regular hook blade requires a lot of power, and inevitably the hook disengages from the shingle, causing you to leave knuckle flesh behind. With the Air Knife, you barely have to apply any draw force to cut through shingles. In fact, the harder you pull, the slower it cuts. And like manual cutting, Air Knife slices a lot faster through hot shingles than cold ones.

Hold the Air Knife without twisting or rotating.
Photos: Mike Guertin Hold the Air Knife without twisting or rotating.

Speed and Capacity. Don't expect the tool to reduce your cutting time much; it doesn't cut much faster than a manual knife–just a lot easier. You also can cut efficiently through two heavy laminated shingles, which certainly saves the triceps workout for the gym. And, at only a 3-cfm draw, you can practically run it off a bicycle pump.

Feel. Air Knife weighs a little less than 2.5 pounds, but feels lighter. The paddle trigger rotates around the body so you can position your hand comfortably for any angle of attack. The spring-loaded stand-off lock keeps the trigger from accidentally actuating, which is a smart feature. The motor is quiet, too, emitting just a dull buzz.

Air Knife comes with two heat-tempered blades. It only takes about 30 seconds to lock a blade securely into the collar with the twist of an Allen wrench. I cut about 8 feet of valley and 6 feet of rake through double layers at the top lap and triple layers at the head lap area of 35-year laminated shingles and the blade slowed only a little. While it had a lot more life left in it, I took a small whet stone and tuned up the blade right on the roof. Fifteen seconds on both sides and it was sharp as new. Or, a 30-second touch-up with a die grinder and it's ready to gobble more shingles.

The Air Knife is perfect for cutting along valleys, but be careful not to cut the flashing underneath.
Photos: Mike Guertin The Air Knife is perfect for cutting along valleys, but be careful not to cut the flashing underneath.

In Use. It takes about 5 feet of cutting a valley or rake to get used to the Air Knife's action. Keep the tool straight with your chalk line and avoid rotating the body; slight wrist twists can cause the blade to drift. Only apply light draw force; as soon as you hear the motor labor, cutting speed slows. The natural reaction is to pull harder, but that bogs the blade down. Ease off and the cutting action recovers.

Take extra care cutting valleys. The deep hook can easily cut through the base shingle layer and you won't notice it. Protect the shingles beneath with aluminum coil stock or a sacrificial shingle.

While the price is a bit high for me, I like the Air Knife. It won't replace my regular utility knife up on a roof but it definitely eases the grunt work slicing valleys, trimming rakes, scoring cap, and cutting pyramid starters. And then there's all that skin still left on my knuckles.

Roof Mates Air Knife: $299; replacement blades: $15 each. 866-766-3628.

–Mike Guertin is a builder and remodeler in East Greenwich, R.I., and is a member of Hanley Wood's JLC Live! construction demonstration team.