My porch has vexed me for a year. It's a covered, enclosed porch, and its floor needed to be repainted. There was old chipping blue paint, a few straggling plastic tiles, and lots of heavy tar holding down the the tiles. I pulled the tiles up and attacked the tar. It was intractable. Hard as wood, tough and adherent, it was impervious to scrapers.
Friends suggested using a heat gun to melt it, and then scrape it up (I didn't try this), acetone (beware the central nervous system damage), and sanding. I tried sanding it down, using a rented sander. The sandpaper gummed up in seconds, and stopped working.
I gave up, finally, and decided to paint over it, a dark green. I painted half the porch, including just a few of the tar-areas, yesterday. I didn't clean up very carefully, tossing my damp rag aside.
This morning I picked up the rag. It was still damp, and the "tar" beneath it had become a soft, pliable, olive-colored paste - yielding easily to a putty knife and washing off completely with a single wipe from the rag! I was dumbfounded. My housie Jon watched this entire exchange, and he and I simply sat laughing at my fortuitous foolishness for five minutes.
I then covered the rest of the unpainted "tar" areas with wet rags for three hours, and came back to attack it some more. The adhesive lay between tar paper and the old blue paint. I discovered a rock-paper-scissors relationship: tar paper beats water, chisel beats tar paper, adhesive beats chisel, and water beats adhesive. Thus, by alternating scraping and soaking, I had the whole floor bear within two hours.
I then proceeded to paint it all green.
And then I found five dollars.