The paint folks are correct…it is essential that you etch the floor prior to painting to ensure good adhesion of the paint. Skip the muriatic acid though, there’s a product called Safer Masonry Cleaner that will do everything that muriatic acid does without the harmful fumes and it won’t burn your skin. Another great option is No-Rinse Concrete Etch. It will etch the floor in as little as 15 seconds, and there’s no need to rinse it. Just wait 30-60 minutes and it’s ready to go.