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Best way to clean underside?

dspur

dspur

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I am scraping the undercoating off with a torch and scraper, and it peels off quite easily (finding some areas needing repair under it).

Once I get it all scraped off, what is the best way to clean the surface to eventually ready for paint. I am using steel brushes of every shape and size on air and battery tools.

What worked best for you? TIA

IMG_5161.jpeg


IMG_5163.jpeg
 
Has anyone used dry ice blasting? I hear it works wonders on undercoating removal.

Another guy soaked the bottom of the car with gas, then used a heated pressure washer and it comes off clean.

I noticed if ATF soaked into the undercoat it comes off easily.
 
Last edited:
Solvent, mineral spirits. Undercoat is tar, a petroleum product.
 
You’re doing a nice smooth job of scraping. I have used industrial degreaser ( dont remember the brand) and TSP , both with great results. Pressure washing in between helps too.
 
I hand scraped the car in my avatar and then rubbed it off with gas and brush painted it with Rust Oleum black in 1981. It has held up well.
Mike
 
R413 said:
Has anyone used dry ice blasting? I hear it works wonders on undercoating removal.

Another guy soaked the bottom of the car with gas, then used a heated pressure washer and it comes off clean.

I noticed if ATF soaked into the undercoat it comes off easily.
Click to expand...
It is on a lift in my shop. Unable to use a pressure washer and wheels / drive train out so cannot move it. Thx
 
I used a large blue tarp to cover the floor under the car. Bought the largest hard sided plastic kid pool to catch most of the wash water. The pool was on top of some plywood and had a set of Harbor Freight moving flat dollies underneath the plywood. I brought a garden hose into the shop for rinsing. A 5 gallon bucket with deluded Simple Green was applied with an extendable car wash hd brush to scrub off what was left of undercoating.

My undercoating was hard and mostly peeled off thankfully. It didn’t need heating.

With the dollies underneath the pool easily move side to side so it would be centered below the work area.

I imagine that if you use a flammable liquid the pool would handle that for awhile. A different brush might have to be used.

The pool was easy to empty after rolling it to the outside. Good luck.

I applied new undercoating as seen along the middle of the vehicle.
IMG_9717.jpeg
 
I used a needle scaler, putty knife, razor blade style gasket scraper, old screwdriver and a dead blow hammer[ for whacking the putty knife or screwdriver] to get the old tenacious as heck undercoating off. Wear eye protection and at least an N95 rated mask. After I've made a pile, out comes the shop vac. I have a lift too. This job would blow doing it on stands.
 
If you plan on re undercoating it down the road, just leave alone till then. Otherwise-----
 
Your undercoating is coming off nicely. Now spray it down with Super Clean and it'll be squeaky-clean.
You can use a spray bottle with clear water and some rags to start with to get all of the gunk off, then
use Paper towels to finish. Alot of the factory primer should stay on the car. Scuff it with scotch-brite
before finish priming. Walmart has Super Clean for $10.86/gal.
 
ckessel said:
I used a needle scaler, putty knife, razor blade style gasket scraper, old screwdriver and a dead blow hammer[ for whacking the putty knife or screwdriver] to get the old tenacious as heck undercoating off. Wear eye protection and at least an N95 rated mask. After I've made a pile, out comes the shop vac. I have a lift too. This job would blow doing it on stands.
Click to expand...
Undercoating is coming off ok with heat and scraper. The task is getting it cleaned up after that.
 
Bird 426 said:
If you plan on re undercoating it down the road, just leave alone till then. Otherwise-----
Click to expand...
yeah not planning on going back with it except in a very few places. When I scraped some of this off I discovered serious damage in a couple places. Frame rail had been filled with foam, and in places the metal was gone but the undercoating covered it. I really want a cleaner look.
 
zyzzyx said:
Your undercoating is coming off nicely. Now spray it down with Super Clean and it'll be squeaky-clean.
You can use a spray bottle with clear water and some rags to start with to get all of the gunk off, then
use Paper towels to finish. Alot of the factory primer should stay on the car. Scuff it with scotch-brite
before finish priming. Walmart has Super Clean for $10.86/gal.
Click to expand...
Thanks, haven't used that but will try it.
 
I've used this multiple times.
Sprayed it, left it, came back and sprayed it again to keep it wet.
Undercoat became a wet goo and scrapped/wiped off.

I sprayed it and left it and forgot to come back and it became a dried out undercoat that basically fell off with a scraper.

In both cases, to get finale residue off, just sprayed, let it sit a minute, wiped off.

20250726_234436.jpg
 
matthon said:
I've used this multiple times.
Sprayed it, left it, came back and sprayed it again to keep it wet.
Undercoat became a wet goo and scrapped/wiped off.

I sprayed it and left it and forgot to come back and it became a dried out undercoat that basically fell off with a scraper.

In both cases, to get finale residue off, just sprayed, let it sit a minute, wiped off.

View attachment 1906360
Click to expand...
I will pick up a bottle and try it too. Thanks
 
There is some impressive power washers that are designed for under carriage cleaning.

stoprust.shop

Frame Flusher (10ft Pressure Washer Attachment)

The Frame Flusher is a high-pressure cleaning tool designed to remove built-up salt, rust flakes, dirt, and debris from the inside of vehicle frames and hard-to-reach areas. Featuring a 190° spray nozzle that directs water both forward and backward, it ensures a thorough flush in a single pass...
stoprust.shop

Just stick it in to frame hole(s) and stand clear? Lol.
 
i've done several, I used a heat gun and scraper, then I wire wheel as much as possible, then wax and greese remover in a spray bottle and a couple rolls of paper towels, wipe it clean, may take a few times. let dry and paint, have had good results.
 
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