I've been dreadfully.. dreadful about (at least) two things: progress on the bus, and pictures of said lack-of-progress. Having mentioned on a few other threads that I've scraped the tar off the roof of this bus, it's time to post evidence ("pictures or it never happened," blah blah!
Here you have one section of the roof after insulation was removed and loose bits brushed away.
Same section, after hot scraping:
This pile of tar junk came from three such roof sections (I think it was just three..):
Finally, most of the process all in one frame:
In text form: I used the 3" metal putty knife shown above, plus the heat gun and buckets of elbow grease, to scrape off as much tar as possible. There's kind of a "sweet spot" with the heat at which the tar becomes soft and scrapes off fairly easily, but then it takes more time to get the next area heated to that point. It took 15-20 minutes per section of roof, except for a session I did in full sun 1-3 pm on a day of above 100 F temperatures. Those sections took "just" 10-15 minutes each. Overall I estimate there were 8-10 hours of work in this step.
After the scraping was all finished I wiped the residue with naphtha. It soiled the rags pretty quickly, and I settled into a two-rag process that worked fairly well. The first rag was soaked with naphtha and was used to wipe down an area. While still wet, the second (less dirty) rag was used to wipe off as much as possible. When the second rag became soiled to the point that it didn't wipe clean very well anymore, the rags were rotated: the first (wet) one was discarded, the second (dry-ish) one became the new wet rag, and a fresh clean rag took on the second-pass role. This step was much faster, probably under 2 hours.
Yet to be done is one more pass with naphtha. In the picture one can see there's still some residue in the top-left corner; I think a second pass like the first should get it pretty clean. Later will come a step of pressure washing (FINALLY!) and maybe de-wax/de-grease prep step before I have foam sprayed on...
I tried MEK, acetone, xylene, and naphtha. All dissolved the tar, but MEK and acetone flash off WAY too fast to be useful. Xylene was kinda OK, but naphtha just worked better. It is commonly found in the paint department at hardware stores and might be labeled "VM&P Naphtha" (varnish makers & painters) or maybe just Naphtha.