During years of finishing concrete in Alaska, Michigan and Wisconsin, I’ve noticed a universal bad habit among concrete finishers: using trowels with edges that are chipped, jagged and razor sharp. Cement masons are usually proud of these tools and will tell you they are “broken in just right.” Unfortunately, no matter how talented a finisher is, that person can’t do a great job with less-than-perfect trowels. Not only are out-of-tune trowels counterproductive, they also can be downright dangerous. Finishers who have never cut themselves on a sharp trowel are as rare as carpenters who have never hit themselves with a hammer. Instead of buying new trowels when mine reach this dangerous condition, I file new edges on them.
First, I clamp the trowel, edge up, in a vise. Then, using a flat file with a piece of wood behind it to keep the file from bowing, I run it the full length of the trowel’s edge in long, even passes. I wear heavy gloves as I do this job, and I let the tip of one of my fingers ride along the side of the trowel to align the center of the file. I typically remove between 1/16 in. to 1/8 in. of metal to dress a trowel edge. Then I turn over the trowel and repeat the process on the other side. Before returning the trowel to my tool bucket, I give it a good coat of WD-40 to prevent rust.
David Whipple, False Pass, AR