The fundamentals of achieving a precise edge.
Whether working on a wall, slab, or any form of concrete pavement, creating a clean and precise edge is crucial. Achieving a sharp edge requires both skill and experience. It’s essential to recognize that not all edges are the same—edging a floor differs from edging a driveway, sidewalk, or curb. The technique varies, and the quality of the edge largely depends on how often the edge is worked.
As with any concrete task, timing is everything. You must identify the ideal moment when the concrete has set enough to work with, but not too hard. The goal is to achieve some stiffness with sufficient integrity, but you need to avoid letting it set too much, which would slow progress.
“The first thing to do before you start catching the edge is clean the top of the form,” advises Nick Demonte, cement mason coordinator for the Operative Plasterers’ & Cement Masons’ International Association (OPCMIA). This step is typically carried out using a margin trowel. You begin by holding the trowel along the edge and gently opening it, then proceed with the edger. However, Demonte emphasizes that the margin trowel should be run on the inside of the form, which is the second step in the process.
The radius of the edge you create depends on the radius of your edger. Demonte recommends starting beginners with a wider 6-inch edger. “We want them to understand the flatness of the edge,” he explains. This training, similar to teaching float usage, is about tool control and adjusting to the concrete’s stiffness.
Another important consideration is the weight of the tool. If the concrete is very wet, edging is still possible, but it requires more experience and technique to avoid the tool sinking. Some stiffness in the concrete helps keep the tool level. Holding the tool at too high of an angle may remove too much cream (or paste), so aim for an angle around 5-10 degrees, ensuring the front of the tool doesn’t dig into the surface.
Body position also plays a role in effective edging. While many prefer working on their knees, Demonte suggests standing to work more efficiently. “Standing allows you to cover more ground,” he says. A wider stance helps maintain balance and reduces strain on your back. Work in one continuous pass, an arm’s length from one side to the other.
Perfecting this technique is key to gaining speed and improving productivity. Consistent practice and a steady technique allow you to edge faster without sacrificing quality.
“There are different techniques for different types of edging,” Demonte adds. For a finished floor, your stance and reach change, but for standard edging, keeping your stance wide allows you to work the trowel effectively along the form’s inside edge.
As you edge, an indentation should form on the outer side of the edge, showing whether the tool has just touched the surface or has dug in. Use your float to smooth the line without disrupting the edge, ensuring the surface stays flat. Continue the technique until the entire slab is edged.
Work with precision and caution. “One of the biggest mistakes is trying to remove a large aggregate rock from the edge,” notes Demonte. “Instead of pressing the edger down to fill the hole, which leads to an uneven edge, work carefully to avoid creating indentations near the form.”
Timing remains a crucial factor, and knowing when to start edging comes with experience. As a general rule, the indentation of the knee board should not exceed 1/8 to 1/4 inch.
Finally, always remember to clean your tools and store them properly to maintain their effectiveness for future use.
