search thread for "%"

I am trying to search the incident summary/thread for "18%" but it is returning everything with 18 in it and ignoring the percent symbol. I can not find anything in the documentation that tells me how to search for a character like this. Is this a special character? I've tried combinations 😫:

"18%"

+"18%"

+18%

+1+8+%

"+1+8+%"

18"%"

+18"%"

18+"%"

18+%

+"1"+"8"+"%"