any tricks for removing undercoating....
 

....from fender wells?

Much of it came off with pressure washing but some patches are stubbornly hanging tuff. Don't want to pressure wash so hard that I blast off the paint.

Tried using heat gun but that seems to make it stick harder

Sorry about crap phone pic

I used a product from Lowes called Black Jack. I think it's a citrus based asphalt remover. You can see how I did in my thread on this.
http://forums.pelicanparts.com/paint-bodywork-discussion-forum/797267-while-im-there-strikes-again.html

Spray it on, let it set a while then use some steel wool or scrub brush to take it off. It worked pretty well for me.

Freez it. A blast of CO2

http://forums.pelicanparts.com/porsche-911-technical-forum/155770-project-73-911-r-rs-week-5-a.html

http://forums.pelicanparts.com/porsche-911-technical-forum/152355-project-73-911-r-rs-week-3-a.html

http://forums.pelicanparts.com/porsche-911-technical-forum/151147-project-73-911-r-rs-week-2-a.html

I tried aircraft paint stripper, orange stripper, heat guns, etc. the only thing that worked and was time efficient was a wire wheel on a 4 inch makita grinder . Not super stiff, be prepared to wear some of the wires. Eye protection, long sleeves required. Gloves up to you, they can snag the grinder. Face protection is a good idea. You can do both in a day. I did the whole interior of my 69, not a great way to spend weekends.

I agree with the wire wheel, some have had success with a air stippler but I just sweat it out with the wire cup brush on a dewalt grinder.

I used a heat gun with a razor blade knife attached to it. When the blade was hot and the heat gun heated the undercoating it came off like butter.
http://forums.pelicanparts.com/uploa...1409626872.jpg

http://forums.pelicanparts.com/uploa...1409626905.jpg

Damn clever, Pat.

It appears that you are attempting to removing some black tar-based undercoating that was applied on top of the factory applied (and lightly painted) chip guard/rocker schutz, and leave the original paint undamaged as much as possible. I removed all the tar undercoating from the bottom of my car one winter - exposing the original paint.

I found the best approach was the following sequence:
1. Heat an area about 1 square ft with a heat gun until you see the tar start to soften
2. Remove the bulk of the tar with a plastic scraper - some will remain in the nooks in the chip guard. My car was undercoated when new, so I found that it had a layer of cosmoline between the tar and paint in most areas which acted as a great lubricant when scraping off the tar to avoid damaging the paint. Plus, the cosmoline melts at a lower temperature than the tar, so this made the removal much easier.
3. Working in smaller areas now, heat the area again lightly and spray on citrus based adhesive remover
4. Use a tooth brush to loosen and dissolve the tar from the nooks
5. Wipe area clean (have plenty of disposable shop towels on hand)
6. Spray the area with citrus de-greaser (note - different than adhesive remover) and wipe down.
7. Once the panel is complete, apply a cleaner wax to remove any remaining tar.

I noticed that the tar did stain the paint in some areas.

Be careful at step 4. If the tar is not dissolving easily, apply more heat. If you are too aggressive with the brush, you will remove the thin layer of paint. For really stubborn areas, 3M adhesive remover can be used instead of the citrus, but be sure to have appropriate ventilation and mask.

The photo below of my floor pan shows Step 6 completed on the left, Step 2 completed in the middle, and the untouched area on the right:
http://forums.pelicanparts.com/uploa...1409628436.jpg

An area of the floor pan after Step 7 (untouched area in background):
http://forums.pelicanparts.com/uploa...1409628611.jpg

Thanks, Frank, for the detailed instructions. Your results are awesome.

Soaking it in WD40 might work. It's worth a try. You probably already have some sitting on your bench

Thought about that Shu....or maybe when pe blaster. I have 4 fender wells to do so I may just try all of the suggestions and see what works the best.

There was a thread awhile back about a guy having success with a multi-tool like this - Oscillating Multifunction Power Tool w/ Variable Speed.

Details here: http://forums.pelicanparts.com/porsche-911-technical-forum/551021-undercoating-removal-fastest-method-yet.html

YMMV.

Good luck! SmileWavy

I'm tellin ya, I did what you want to do. Don't waste your time with ANY of the big box store citrus cleaners. If you can find the ZEP orange cleaner that asphalt companies use, that would be my first choice. If you can't find that, the Black Jack from Lowes is the next best thing.