I accidentally used my exterior paint instead of my primer paint while painting my balcony. There was about 50% wood showing. I want to go back and primer prior to putting on another coat of exterior paint. Is there an issue with this and is it necessary?
At this point priming is neither necessary nor helpful. Apply a second finish coat and wait. If, after some time, the finish does not adhere, scrape off what you can and prime at that time. Don't worry, the situation will let you know what to do, just do not allow too much bare wood to be exposed if the finish begins to peel.