Please read the instructions! All SLC's that I'm familiar with require the primer. SOme even have different ones depending on the surface, or if the same, different requirements on application of the primer. One of the biggest mistakes people make with slc is not believing the set time...depending on the temperature and the version you select, you can have as little as 10-minutes before things start setting. At that point, you can't do anything. Another mistake is that people don't use enough. It works much better if you make the pour deeper than you think you need. Check out www.johnbridge.com to get some help on this.