I used to hold this thing like a baseball bat-turns out that's why my arm ached and my mortar was all over the place. A pro watched me for 5 minutes once and said, "Let me fix that-you're holding it wrong." Here's the right way, step by step.
First, grip the handle with your dominant hand-your fingers should wrap around the handle, but not too tight. If you squeeze too hard, your hand gets tired fast, and you lose control. I used to death-grip mine, and after an hour, I could barely close my hand. Keep it loose enough that you can move your wrist easily.
Next, rest the base of the trowel's blade against the palm of your non-dominant hand. Let me repeat that-don't just let your other hand hang there. Your non-dominant hand should support the blade, kind of like a shelf. That takes the weight off your dominant arm and helps you keep the blade flat. I skipped this at first, and my blade would tilt, leaving uneven mortar.
Then, angle the blade slightly when you're spreading mortar-about 15 degrees from the brick. If it's too flat, you can't spread the mortar; too steep, and it falls off. I practice this by holding the trowel over a bucket first-get the angle right before touching the brick.
Also, keep your elbows close to your body. I used to hold my arm out like I was balancing a plate, which made my shoulder sore. Keeping your elbows in gives you more control and keeps the trowel steady. It feels weird at first, but after 10 minutes, it becomes second nature. Trust me, once you get the grip right, everything else-spreading, loading, buttering bricks-gets way easier.
brick trowel from hanke tools
