Let's get one thing straight: You can use a corner trowel for concrete corners, but it's not the same as using it for drywall. Concrete is thicker, heavier, and dries faster than joint compound-so you need to know the tricks to make it work.
First, let's talk about the trowel itself. A regular drywall corner trowel (even stainless steel) might not be tough enough for wet concrete. Wet concrete is abrasive, and it can scratch or bend a flimsy trowel. If you're going to use a corner trowel for concrete, get one that's made for masonry-they're usually thicker (16-gauge steel or more) and have a stiffer blade. I once tried using a drywall corner trowel on a concrete patio corner, and the blade bent slightly-total fail. I switched to a masonry corner trowel, and it handled the concrete like a pro.
Second, timing is everything. Concrete dries fast, so you can't take your time like you can with drywall compound. You need to use the corner trowel while the concrete is still "workable"-not too wet (it'll slump off the trowel) and not too dry (it'll crumble). It's like making pancakes-you have to flip them at the right time. I usually wait 20 to 30 minutes after pouring the concrete, then test it with my finger: if it leaves a slight indent, it's ready.
Third, technique. With drywall, you pull the trowel slowly-with concrete, you need to press harder and move a little faster. Wet concrete is heavy, so you'll need to apply more pressure to get it into the corner and smooth it out. Also, have a bucket of water nearby-wipe the trowel off after every pass to keep concrete from building up on the blade. If concrete dries on the trowel, it'll ruin your finish.
Is it easy? No-concrete work is harder than drywall. But if you're doing a small concrete project (like a garden wall or a step), a corner trowel can give you a clean, smooth corner. Just make sure you have the right trowel, work fast, and don't be afraid to practice on a scrap piece first. And if you're doing a big project (like a foundation), you might want to hire a pro-concrete corners are crucial for structural integrity, and mistakes are hard to fix. But for DIY jobs? A corner trowel works-just be prepared to get a little messy.
