Tar-like undercoating removal

[Honeydipped]

Hey everyone, I have a 2003 All American 8.3L RE. On parts of the undercarriage of my bus there is a layer of tar like substance that must have been used as some sort of protective treatment. The issue is that in some parts it has chipped off or has a small crack and as a result water has gotten in and created rust. As such, I would like to remove this coating so I can treat with rust converter and then a protective enamel.

The issue is .. it is tricky to remove!

I’ve tried a hand held wire brush to no avail, the undercoating just laughed at my feeble attempt.

I’ve tried knotted wire on my angle grinder. It works OK but it is slow going because if I hit one area too long it warms up the tar and just smears it around or flings tar on everything else. Luckily Ohio has been getting relatively cool at night so I can hit an area for a few seconds and then let it cool down.

Using a scraper by itself doesn’t really work too well, but I’ve also tried scraping with a heat gun. It works kinda OK, but is very slow going and does not create a nice finish (there are little bits and pieces left on the metal).

Does anyone have any tips or tricks? Should I even worry about it and simple just try to TSP the surface and roll enamel over it? I would really prefer to remove it, but if it isn’t worthwhile then I could skip I suppose. Is there some sort of solvent that I can use to “dissolve” it away?

Any feedback would be greatly appreciated. Thanks so much!

[musigenesis]

I had the same problem on the underside of my bus. I've dealt with it so far by removing most of it physically with a painter's tool (hand scraper) and then spraying mineral spirits on it with a spray bottle. And then wiping and wiping and wiping and wiping.

[Honeydipped]

Originally Posted by musigenesis

I had the same problem on the underside of my bus. I've dealt with it so far by removing most of it physically with a painter's tool (hand scraper) and then spraying mineral spirits on it with a spray bottle. And then wiping and wiping and wiping and wiping.

Thanks for the feedback on your experience! Since I’ve posted I’ve quit using the wire brush/angle grinder. It was just causing a mess. I’ve been going the painter’s tool route for now. I’ll grab some mineral spirits tomorrow and try to dissolve the bits that the painter’s tool leaves behind.

Reading online on car forums I’ve seen people suggesting aircraft stripper? Anyone have any experience with that or should I stick with mineral spirits?

[Native]

Aircraft stripper is powerful stuff. Should you go that route, please be careful and follow all of the precautions on the label.

[EastCoastCB]

Originally Posted by Native

Aircraft stripper is powerful stuff. Should you go that route, please be careful and follow all of the precautions on the label.

Yeah its VERY harmful to the eyes and skin.
I go full respirator/face shield/Total body protection when using aircraft stripper on anything large.

But I removed ALL the asphalteum from a 40' bus. It was brutal. The aircraft stripper was by far the best thing for removing it. 2 hours labor with manual methods is equivalent to about 2 or 3 minutes of light work with the stripper.

[Honeydipped]

Thanks Native and CB. That’s really good to know about the aircraft stripper. It sounds so tempting knowing how well it works but I might just stick with the mineral spirits for the bulk of the work and perhaps I’ll get a bottle of the stripper for the really hard to get to areas. I’ll be sure to wear a lot of PPE if I go the stripper route. Thanks again everyone, I can’t express how much I value this sites feedback.

One quick question - what brand of aircraft stripper did you get?

[ol trunt]

I found that the stuff chips off easily when cold (here about 40 degrees). The original linoleum in my bus was glued down with it. The lino came right up but the tar gave me the same problems you are having until I discovered the cold trick.
Jack

[Honeydipped]

Originally Posted by ol trunt

I found that the stuff chips off easily when cold (here about 40 degrees). The original linoleum in my bus was glued down with it. The lino came right up but the tar gave me the same problems you are having until I discovered the cold trick.
Jack

Thanks Jack! That’s definitely another option. Just wait a bit for temps to get colder and work at it that way. One thing I read online is some people get a little brick of dry ice and wrap it in a towel, then they hold the dry ice to the tar and chip it off that way. Maybe I’ll invest in a pneumatic scrapper and some dry ice if I get tired of doing it the other ways and its still warm enough to be an issue.

I think I’ll do a bit of what everyone suggested to break up the monotony

[~Pat~]

Just curious, if it is that hard to remove then why do so? Except for areas needing repairs. Disclaimer... I'm still deciding between bus or cargo trailer.

[Honeydipped]

Originally Posted by ~Pat~

Just curious, if it is that hard to remove then why do so? Except for areas needing repairs. Disclaimer... I'm still deciding between bus or cargo trailer.

In some spots it is cracked and letting moisture in behind the coating. While the coating may look fine on the exterior, underneath could be a bed of rust. My thinking is if it is an area that looks like it may get wet, I’d rather remove the coating, treat the metal with a rust converter if needed then do some top coats of primer and solvent based enamel. I plan on having this bus for many years and I’m thinking a little preventative maintenance may reduce some headache and sheet metal work down the road. Also, this bus is currently in Ohio and probably will be for a few years at least. With how corrosive Ohio roads can be due to tons of salt added to the roads, I don’t want this to be something I wish I would have done.

Granted I’m still fairly new to all of this.. so I’m not sure if these are entirely the right steps to take, but I guess I’d rather be safe than sorry. If I’m going in the wrong direction I’m definitely open to just doing the obvious problem areas.

[Jolly Roger bus 223]

is it like a bedliner or undercoat product?
just take care of the split or bad areas and the auto stores sell either spray cans of it for repairs or DIY kits of roll on for a full bed.
scrape and clean the troubled areas and if you go with either of what i recommended read instruction for the one you choose before you prime or whatever the trouble areas.
could be your trouble areas are because the manufacturer didnt clean all the oil off of the steel before they applied.
the roll on bed liner is made to go over paint?
the spray stuff that i have used was self etching which means that it eats into the metals a little to grab and hold on and i dont remember which brand. but one of them didnt grab onto an already painted yellow panel.
wish you luck

[musigenesis]

Originally Posted by ~Pat~

Just curious, if it is that hard to remove then why do so? Except for areas needing repairs. Disclaimer... I'm still deciding between bus or cargo trailer.

I have the same problem. In some places on my underside (mainly on the insides of the skirts and underneath the driver's seat) this asphalteum is in great shape, with all the metal underneath it basically like new. In these areas I've leaving it alone, but on the rest of the underside it's only adhering in rough spots and patches. I suppose you could de-rust and paint up to the edges of it, but probably the rust would continue getting under what remains of it.

Probably the quickest and dirtiest method would be to ospho the exposed rust and then apply another layer of this undercoating.

[EastCoastCB]

Originally Posted by ~Pat~

Just curious, if it is that hard to remove then why do so? Except for areas needing repairs. Disclaimer... I'm still deciding between bus or cargo trailer.

It traps moisture. This is what was behind mine-

[Honeydipped]

Hey everyone, I just wanted to give a quick update and suggest to people my new favorite tool. I picked up a compact air needle scaler (https://www.harborfreight.com/compac...ler-96997.html). Sweet baby Jesus do I love this new tool. It’s amazing at getting rust scale off and it works pretty well at chipping off the tar like undercoating! If you’re looking for something to make quick(er) work of rust remediation under your bus I can’t suggest this thing enough.

I’ve been using it for a few hours and what would have taken me 3-4 hours with my heat gun, paint tool, wire brush, and hammer I was able to do in like 45 minutes. While I haven’t broken any needles yet, it was suggested to get a replacement pack of needles when they do eventually break (they are a consumable - https://www.harborfreight.com/needle...-pc-62483.html). The needle scaler is also really great at getting in the nooks and crannies since the needles aren’t very big in diameter. Also, be sure to oil the tool regularly and wear ear protection - this thing is as loud as the dickens.

For underbody coating it works best on the “virgin” coating. The stuff I melted and smeared with a angle grinder/wire cup brush or heat gun/paint scraper was harder to get off with this tool; I’ll have to get that off with mineral spirits as previously suggested. But the stuff I hadn’t tried to remove yet chipped right off no problem. While typically I’m a firm believer in getting what you pay for, and I don’t shop at harbor freight too often, I wanted to try their cheap one just to see if I liked the needle scaler route. Once this thing does bite the dust, I’ll probably pick up a more robust needle scaler. I like it that much.

[musigenesis]

Originally Posted by Honeydipped

Hey everyone, I just wanted to give a quick update and suggest to people my new favorite tool. I picked up a compact air needle scaler (https://www.harborfreight.com/compac...ler-96997.html). Sweet baby Jesus do I love this new tool. It’s amazing at getting rust scale off and it works pretty well at chipping off the tar like undercoating! If you’re looking for something to make quick(er) work of rust remediation under your bus I can’t suggest this thing enough.

This looks good. I'm thinking of getting one even though I have a 6 gallon pancake compressor. The HF air chisel is also not supposed to work with a pancake but I've found it works fine - I tend to go slowly anyway.

[Honeydipped]

Originally Posted by musigenesis

This looks good. I'm thinking of getting one even though I have a 6 gallon pancake compressor. The HF air chisel is also not supposed to work with a pancake but I've found it works fine - I tend to go slowly anyway.

I think it would work as long as your compressor has the required psi. The air scaler seems to like the air line regulated at 90 psi. A smaller tank just means your compressor will kick on more often, so as long as you go slow not to overheat the compressor it would probably work. It does go through a good amount of air so definitely go slower.

Edit: HF also has a 20% of coupon that is good for the scaler (https://go.harborfreight.com/coupons...arbor-freight/) and if you do want to upgrade compressors they also have a couple of their compressors on sale (https://go.harborfreight.com/cpi/dig...r-coupon-book/). I’ve been using the 20gal oiled McGraw. It’s not the best compressor in the world but it’s holding up so far with regular oil changes.

[Native]

Thank you for the air needle chipper and replacement needle links. I have them bookmarked, which I hope will translate to a purchase.

[StudioCoot2020]

The only best way to remove this mess is with dry ice blasting. Witn the cold effect (-79,5. Degrees) is just fall of without damaging the underground. What is left is dry dirt.