Six months ago or more, my friend used a 2-part epoxy (no longer have the packaging, but it's a double-syringe with clear liquids, purchased at Home Hardware) on something, and some of it (one or both liquids) got on our basement floor, which is concrete someone had painted grey before we moved in. Well, the reaction between the epoxy and (I had thought) the paint smells like a burning rag of cat pee. After the nth cleaning of it with vinegar and baking soda, I one day just duct taped it over to at least stop the smell, since it was winter and (enough) fresh air (for this particular smell) was hard to come by in our house without central air without us freezing to death.
Today I decided to try sandpaper, and sanded down to the concrete, and no matter how much I sand I can now see the outline of the spill in a grey-brownish shadow on the white concrete, and I can still smell the damn stuff. I smell three inches away on the floor and it smells neutral. It's just that one spot, and it can stink up the whole room if I leave it.
What will take care of the smell (while not adding another smell to take care of)?