The benefit of evaporust is that it won't consume the base metal, only the iron oxide. A similar, but less effective, result can be had from a dilute mixture of feed-grade molasses and water. 9 parts water to 1 part molasses. The molasses takes a week or 2, but gives pretty impressive results. Evaporust and molasses both work on a process called Chelation. Both of these will dissolve the iron-oxide but not the base metal (with exceptions I outline below).
If you search, use "molasses chelation" and you should get many hits. I've used it very successfully on hundreds of parts, but have had 2 mishaps that I'll share....don't want anyone else to make the same mistakes. I left some sheet metal braces in the tank for at least 6 months....the tank had evaporated probably 20% of the water away.....the parts came out pitted in some areas....that was the first time that had ever happened and, by far, the longest soak. Bottom line, it was my fault for leaving them so long. The 2nd case was a std bore cleveland block I had planned to rebuild. I had mixed a fresh batch and due to circumstances, did not follow the 9:1 ratio.....it was probably closer to 6 or 7:1. I left the block soaking for 3 weeks. Again, there was some strange pitting in certain parts of the block and none in others....it was really strange. That being said, I've left parts to soak for several weeks and had no issue with the 9:1 ratio....typically, 2 weeks is all that is needed.
Stay with 9:1 and don't forget your parts and let them soak for months....pay more attention to cast iron parts.
This is a pair of headers that were leaned against an outside wall for something like 20+ years. This was after a 2 week soak and power wash right out of the tank.
Edited first paragraph.
Vern
