Because of effloresence appearing on my porcelain tiled deck after rain events, I am planning to replace the existing grout with epoxy grout which will create a waterproof barrier. But I first need to remove the existing grout joints, which are < 1/8" width. It's my understanding that porcelain tiles can be susceptible to chipping so I'm not certain which method would be most appropriate to perform this work. I was considering using a grout blade on my oscillating tool, but I wanted to get some feedback before proceeding.
There is a Dremel Grout removal attachment, which consists of a fixture to hold the tool at a 45 degree angle, and you can get a 1/16 inch carbide cutter bit.
I've used this setup several times to remove grout for renewal or tile replacement. It can work quite well if the grout is really a sixteenth wide. Its not easy, but you can chip the tiles if you're not careful. I inevitably break the bit, and will always buy at least two.
You will run the least amount of risk of chipping the tile if you do the job with hand tools. Use a 1/16” carbide grout saw, and you don’t need to remove all of the grout to the bottom of the tile, just more than 1/16”. Pulling the tool is safer for the tile than pushing it.