Tried using a 4-inch drywall knife to spread seam sealer and it left a huge ridge I had to sand for an hour. | Carpet Installers - Freelance Forum - The Community for Independent Professionals
Honestly a 4-inch knife should work fine if you're using it right. Maybe you just had too much mud on the blade? That stuff needs to be spread super thin, almost like you're scraping it off more than laying it down. A wider knife can help you see the high spots better, but the real trick is in the wrist. You ever try pulling it at a lower angle?