Scraping undercoating off the back side of a painted fender

[bull]

How might the heat from a heat gun effect the painted surface on the other side if I were to attack the factory undercoating inside the fender? I wasn't planning on doing this but it seems I'm detecting some surface rust beneath some factory undercoating. I bought a Wagner 500-1,000 degree heat gun the other day and have been working on removing the undercoating out from the front wheel wells with a putty knife. That's when I noticed the surface rust.

[TexasStroker]

I don't think the heat gun would do any damage...provided you don't set it to hot and leave it concentrated in one spot for a long duration.

Now a torch I would be leary of...I messed around with different tactics on the rear wheel wells when I did the trunk floor.  The torch would help, but generally smoked the stuff and made things somewhat tacky.  The heat gun really didn't get going...I literally got burned out before it was of any help.

Everyone I talk to (old timers atleast) swear by the propane torch and just scraping it off like butter.  I did get some good results, but to me the mess and fumes created were not worth it.

As idiotic as it sounds I just go about things the old fashioned way with a scraper, lol.  It does make a mess and the stuff gets all over you, but it works and is easy to clean up...most importantly you don't risk any unnecessary damage that way.

I'm, like yourself, in the front wheel well now.  The paint that  I drove thru NYD does not come off the undercoating up front...way too irregular of a surface.  The two choices were spray black over the paint...or loose the undercoating, prep, and paint.  Obviously I went with option two.  I was afraid to even use the torch given the potential for something bad to happen with the flip side being the painted RH fender, and the heat gun really didn't seem worth the time.  You might have different results though...

I do think a spray down with some grease remover loosens things up a tad...but maybe it is psychological, lol.  I know the back pain isn't 

Good luck and let us know what works best for you. 

[tan top]

 true  don't keep it in one spot for too long  , also that  undercoating builds up & holds heat  for quite some time ,     

[Patronus]

 
use the torch, dont keep it in one spot. Heat an area and move on, then go back and heat it again, it will retain the heat and become soft. For the fumes I just use a fan.   

[bull]

That heat gun I've been using actually works pretty good. I only have to wave it over a spot roughly six inches long for 20-30 seconds before the undercoating is ready to come off. Sounds like it will be fine if I don't get crazy.

[Troy]

I use a knotted (braided) wire wheel on a grinder and it doesn't seem to heat the metal at all. Makes a big mess though!

Troy

[Aussiemadonmopars]

Dude, go the heat gun with the 1" putty knife. I used it and got most of it off with the knife. While the heat is still in the panel use a rag soaked in Kero to wipe off the excess that is left. I did the whole underside of 2 cars like this.

[Charger-Bodie]

In your case bull, I would use the putty knife and scrapers . I wouldnt use any heat. One spot of too hot and you will be repainting a fender.

Also. Make sure you guys get some thick undercoating back under there! It needs to be there to absorb the impact of small rocks and stones picked up on the road. If the undercoating is not there you will begin to see tiny "up" dents on the outside surface of your fenders.

[Back N Black]

In your case bull, I would use the putty knife and scrapers . I wouldnt use any heat. One spot of too hot and you will be repainting a fender.

Also. Make sure you guys get some thick undercoating back under there! It needs to be there to absorb the impact of small rocks and stones picked up on the road. If the undercoating is not there you will begin to see tiny "up" dents on the outside surface of your fenders.

Brian what do you suggest for undercoating?

[Charger-Bodie]

My first recomendation would be the heavy stuff from restos by Rick. Second would be the heavey body shutz from 3M.

[bull]

I'll have to take the fenders off to do it. There's no way I'm going to try doing that overhead when I can just pull the fender off and set it on a couple of padded stands. The stuff is pretty thin on the fenders compared to the rest of the wheel well areas so maybe it won't be too bad without heat. I wish I'd have had the foresight to do this before having the car painted. I'll just add that to my growing list of coulda/woulda/shoulda.

One other thing. Since I'm just going to reapply undercoating is there any reason to remove all the residue? By that I mean when you scrape the stuff off there's almost always a film of "tar" left on top of the metal. Is there any reason I should clean all that stuff off too or can I just spray new undercoating over the top of it?

[twodko]

Propane torch, heat gun etc have a fire extinquisher handy in your shop/garage.......always.

Tom

[69*F5*SE]

Bull, just be careful not to push too hard when scraping if you have to so that you don't scratch off any paint and primer to bare metal etc. or you'll just create way more problems than you started with.  Don't ask me how I know this.      Maybe a hard plastic type scraper would work and cause less chance for scraping through to bare metal.  Ted

[bull]

I know there are a couple of small spots that went down to bare metal. What did you do with yours?

[TylerCharger69]

use the torch, dont keep it in one spot. Heat an area and move on, then go back and heat it again, it will retain the heat and become soft. For the fumes I just use a fan.   

And for the "drippings"...just put down some cardboard or maybe some black felt paper (used for roofing) that you can throw away!!!

[68blue]

I took undercoat off by mixing xylol and MEK 4-1 then soaking paper towels in it and laying on the undercoat very wet. Covered that with plastic sheet and waited a few hours. Turned the undercoat into something like grease which I used the wet paper towels to wipe up. Had to scrape a few stubborn spots. It was really the only way I could get the stuff off as sanding or scraping alone did not work very well.

[Charger-Bodie]

use the torch, dont keep it in one spot. Heat an area and move on, then go back and heat it again, it will retain the heat and become soft. For the fumes I just use a fan.  

And for the "drippings"...just put down some cardboard or maybe some black felt paper (used for roofing) that you can throw away!!!

I think the thing that you guys may not realize,Is that bulls Charger is painted and he needs to be careful not to disturb the finish on the outside of the fender.

[Troy]

use the torch, dont keep it in one spot. Heat an area and move on, then go back and heat it again, it will retain the heat and become soft. For the fumes I just use a fan.  

And for the "drippings"...just put down some cardboard or maybe some black felt paper (used for roofing) that you can throw away!!!

I think the  thing that you guys may not realize,Is that bulls Charger is painted and he needs to be careful not to disturb the finish on the outside of the fender.

Right! No torches!

Troy

[bull]

Yes, a torch is about the last thing I'd use at this point, on the fender esp. I had some pretty good success scraping the undercoating off the inner fender area today with a putty knife alone. Got it all done in about 1.5 - 2 hrs of scraping without heat. I used the heat gun on a few small areas that were not directly opposite the inner fender. Once you get under the edge of that stuff it peels off fairly well and after I pulled the fender off I had lots of room to move. I put the fender on a fender stand but haven't started working on it yet.

I'm thinking about either rolling or brushing on some primer once it's all prepped to deal with the few bare spots I created with the putty knife. I really don't need overspray everywhere which leads me to wonder about the undercoat reapplication process. There are some areas of surface rust that I plan to use SEM Rust Seal on.

A piece of advice for those about to start on the painting process: Make sure you've got at least the front wheel wells dealt with before you get too crazy on the outer body. I wish one of my body shops would have offered me this piece of advice because I sure didn't think of it beforehand.

[TylerCharger69]

My bad....i was thinking undercarriage

[TexasStroker]

I'm about burned out on scraping.  I've done very little on the top or exterior (in this case backside of the painted fender).  The rest is a cake walk.  I do it the old fashioned way with a scraper...takes awhile and makes a mess, but really not too bad. 

The backend is of course where most of the paint went and it and the front are cleaned up pretty good.

The actual fender sides (overhead and out) have thin stringers of white paint all over the place.  Not wanting to eat any more undercoating for the night I tried soaking rags in mineral spirits...the surface is just too irregular for that to be effective.  Not sure why I thought it would work tonight when it didn't in the past...guess it was a last ditch effort.  Essentially you'd have to "wipe" the white paint off WITH the undercoating going with it :s

The factory's undercoating was very thin on these sections of the front wheel well...the back corner barely has any and the brace created about a 2" chasm in the application process.  Despite the surface thickness it is still enough to keep it from just wiping off or coming off with a light scraping.

The rear wheel well, altough painful after a few hours and very messy, was a cake walk to rid of the undercoating compared to the front.  And there was no need to worry about damaging any painted surfaces.

I really think the best way to get at it is to pull the fenders like Bull wound up doing.  If nothing else you'll be ABOVE the undercoating and won't get showered with it 

I am really considering just prepping everything and spraying the undercoating on the cleaned up segments...and then maybe spraying over the white paint on the fender sides with black.  There aren't any rust issues so the fender coming off isn't a necessity.  This is something I had on a to-do list for the fictional day when I might have free time, but frankly I miss driving the car after getting it going after so-long.  If the paint wouldn't have been in the road I'd have spent all this time re-doing the insturment cluster as opposed to living around the RH rotor 

The wheel wells always look sharp with a fresh undercoat and given on 2nd Gens the main thing you see is the back portion it will look great...The fender itself would remain virgin from the factory...with some paint shot over the aged undercoating 

Like Bull said, if you are anxious to get your car pained, take the extra day to get the inner fenders and wheel wells all cleaned up and coated with something.  It will save you headaches later on like he is experiencing and if you use something smooth and thick as opposed to rough and thick you will be able to "wipe" paint off should you ever be so unfortunate as to drive thru some 

[bill440rt]

Have you considered using this from Eastwood?

http://www.eastwood.com/under-gone-undercoating-remover-aerosol-17-oz-net.html

Might be worth a shot. At least you can contact them to see if it's safe for paint.

[TexasStroker]

Have you considered using this from Eastwood?

http://www.eastwood.com/under-gone-undercoating-remover-aerosol-17-oz-net.html

Might be worth a shot. At least you can contact them to see if it's safe for paint.

Nice!  I will look into that...I know a few folks that order regularly and if they haven't tried it, maybe I can get it tacked on their order.  That would be ideal for me as the only reason I'm in the situation is the fact the white paint the car went thru is all over everything...and it bothers me 

Provided it works it would be a very much appreciated product on the market place.

[bull]

Some fine print: "Undercoat removal made easy! Here's the solution for undercoats that can be imprinted with a thumbnail."

I don't think my hard-as-a-rock factory undercoating qualifies as something that can be imprinted with a thumbnail. I think the undercoating would make an imprint on my thumbnail instead.

[TexasStroker]

Haha, I wondered about that.  There were a few places, mainly nooks and corner, where I could possibly cut through with a fingernail...the rest if very hard, but I assume at some point years ago was probably imprintable with a thumbnail?!  That is why I am asking...if it was local I'd try it, but having to pay freight to get something that might not work never interested me much.

If anyone has tried it, let us know...