Nah, a brick trowel can't really replace a margin trowel-they're like a wrench and a screwdriver, y'know? Both tools, but for totally different jobs. Let's break it down: a margin trowel's small-blade's only 3 or 4 inches long, thin, usually flat.
It's for detail work: scrapin' mortar out of tight gaps, mixin' small batches of mortar (like when you're patching a brick), or spreading mortar in tiny spots a brick trowel can't reach-like around window sills or between two bricks that are super close.
A brick trowel's big, thick, blade's 6 to 8 inches long. It's for hauling mortar and spreading it on big bricks. Try usin' a brick trowel to scrape mortar out of a 1-inch gap-you'll just push mortar further in, or scratch the brick. I tried that once when I couldn't find my margin trowel-ended up makin' a mess, had to redo the whole section.
Now, could you sort of use a brick trowel for tiny jobs in a pinch? Sure-if you're out in the field and forgot your margin trowel, you can use the tip of the brick trowel to spread a little mortar. But it'll be messy, take twice as long, and the work won't look as clean. It's like usin' a spoon to spread peanut butter on a cracker-you can do it, but a knife's way better.
So no, don't replace your margin trowel with a brick trowel. Keep both in your toolbox-margin for details, brick for big stuff. That's how you do it right.
