No, volunteering is regarded as work, so need a workpermit, since it will take the jobs away from Thai people who could make a living by doing that job.
Search your Thai Embassy website for volunteer visa.
Every Thai Embassy has their own way of doing things, so when asking a question you HAVE TO tell which Embassy you want to / applyed at, or it is impossible to give correct answers.
But start by searching the group, for posts about that specific Embassy.