If you make a strong enough mix, you'll just replicate the existing problems with OPC. But generally, you can DIY a cement with roughly 1/3 hydrated lime and th

If you make a strong enough mix, you'll just replicate the existing problems with OPC. But generally, you can DIY a cement with roughly 1/3 hydrated lime and the rest graded dust-3/4" pozzolonic stone. Let me know the impact of acquiring that if you aren't in Italy or, apparently, southern Idaho. You can do it with non-pozzolonic stone but using ~2:1 lime:crushed terracotta, but it won't have the magic healing properties of the original. (Note, going off memory on the ratios; they're probably somewhat off).