My girlfriend bought a cafe and they had a cast iron waffle iron that had, in some places, 5mm of grime built up over 2 years, never once been cleaned. Even the hinges were full of old crusted on batter and grease.
I spent hours with a grill scraper scraping every individual pin.
I have gotten to or past the seasoning in many places except in between all of the pins is hell to try to scrape the old baked on grease away. I have tried sodium carbonate soaks, a wire brush and a wire brush on a drill, a few different scraping tools, and I have only gotten about half out of those grooves. Miles better than before, but still not perfect enough to season and put back in the cafe.
Well, the plastic bags keep the lye from drying up. You want a bit of liquid sloshing about in the bag for the 2 days. When you apply enough of it via spray, you’ll know, because the lye will collect in the corners of the press and in the bag. That’s why I mentioned the safety precautions. Breath mask to protect you from the fumes, serious gloves to protect you from the sprayed and liquid lye.