Great question-one I get all the time. Let me start with a straight answer: it depends on the type of vinyl flooring you're using. I've laid both peel-and-stick and glue-down vinyl, and they're totally different beasts.
First, peel-and-stick vinyl. These are the ones with adhesive already on the back-you just peel the paper and stick 'em down. For these? No, you don't need a notched trowel. In fact, using one would be a waste of time (and maybe even mess up the adhesive). I did a bathroom floor with peel-and-stick vinyl last year-just cleaned the subfloor, peeled, stuck, and done. Took me 2 hours, no trowel needed.
Now, glue-down vinyl-this is where things change. Glue-down vinyl (either sheet vinyl or luxury vinyl planks/LVP that need separate adhesive) does need a notched trowel. But not just any trowel-you gotta match it to the thickness of the vinyl. For thin sheet vinyl (like the 1/16-inch thick ones), a 1/16x1/8-inch V-notch trowel is perfect. It spreads a super thin, even layer of glue-just enough to stick, not so much that it seeps up between the seams. I laid sheet vinyl in a laundry room once with this trowel, and it's still holding strong 3 years later.
For thicker LVP (like the 1/4-inch thick ones), you need a 1/8x1/4-inch square notch trowel. Thicker vinyl needs more adhesive to stay put, and the square notches hold just the right amount. I did a living room with 1/4-inch LVP last month, used this size, and the planks didn't shift at all-even when my client's dog ran across 'em the next day.
One big mistake I see: people using a flat trowel for glue-down vinyl. A flat trowel spreads glue too thick, and it'll seep up between the seams, making the floor look messy and sticky. I had a buddy who did that-his vinyl floor looked like a disaster, and he had to scrape it all up and start over. Don't be that guy: use a notched trowel for glue-down, skip it for peel-and-stick.
notched trowel from hanke tools
