Mine revolves around coatings. Anything that's something you mix then spread (like grout) you need to be absolutely sure that everyone mixed it correctly. I lost my tiler, and my new one seemed really good. He did a shower, a few months went by and we were on another tile job when the shower client called us with something that was off with their grout. We went and inspected it and the grout had failed. We had just grouted the current job and that grout was failed too (thank God we caught it). Long story short, he was just mixing grout the way he always did it but wasn't doing it per manufacturers instructions. Too much water and it was failing. Such a pain in the butt to fix.
What I learned is anytime something is being applied, me as the project manager needs to make sure that I am doing the research to find out what the correct mixture/ application is and putting that in my job notes. Ask them to post pictures of the correct mixture being done. Something that's often over looked can turn in to a massive head ache.
