Grinding paint off

[Datsun-Fever]

Hey guys i have been grinding the pain off of my car and it leaves a little uneveness, is this ok as long as i use filler when im done stripping the whole thing? thanks.

[my_mad_z]

Gringind the paint off with what? You have to be very careful if you are using a grinding disc or very course sandpaper. If you put too much heat into the body, the panels will warp. I would suggest using paint stripper to remove the paint!

*Scuff the paint (by hand) using course sandpaper - don't push too hard or you will dent the panel;

*Apply paint stipper as per directions;

*Cover the paint stripper with plastic;

*Wait for the paint to fry (bubble up);

*Remove with scraper.

By scuffing the paint, it allows the paint stripper to work more effectively. Covering the application of paint stripper seams to be more effective as well.

Sand blasting is another alternative but it can warp the panels.... I would stick with paint stripper as it doesn't warp or damage the metal.

My 2cents, hope it helps.

Marc.

[Walter Moore]

For the record I removed the paint from my 71 with 36 grit sandpaper and a 7" disk sander. But then the body on my car is so beat up that there was very little concern about warping...

In fact nearly 25% of the surface of the car was covered with bondo, so paint stripper would have been on very little value.

A friend, now dead, who worked in a string of body shops over the years recommended sanding the paint off. His exact words were "Just 40 it." Which he later explained meant to remove the paint with 40 grit sand paper.

Of course I was doing this in the dead of winter, in a poorly heated garage where the temperature never got up to 45 degrees F, so heat was the least of my problems.

[zed240au]

To me the best way to remove paint is first paint stripper chemical then was that off and use 3m clean and strip wheels they fit on to a drill and strip paint off but only polish metal so there great

Mick

[Datsun-Fever]

Ah, i got pretty far with grinding it, i only do it untill most of the paint is gone, then i give it a little sanding, but of course there are very small scratches in the metal, will a primer fill these or will i need a filler? if so what should i use? thanks.

[zed240au]

some scratches are ok but none is a lot better filler will fill them baut you some times end up with it shrinking when you paint it and the cracks just come through again which means more sanding may get away with primer filler using a spray putty gun that works well

Mick

[EScanlon]

OK, we'll not go into the unadviseability of removing the paint with a grinder.

But now that you have gone and done it, (See Ollie?) you have literally forced yourself into a paintiing "corner". It will take several shots of Medium High fill with sanding between them before you'll be happy with the smoothness of the panels. Trust me on this one, what doesn't "look bad" when you are up close on an unpainted fender turns out to look like a golf ball cover when you paint it.

When you spray primer you are addressing 2 jobs. The first is the chemical bonding to the metal. This ensures that the metal will not slough off the paint at the first flex or chip that occurs. The second is to provide a film agent that covers all of the bare metal to where the paint can adhere to the primer. Usually most bodymen will shoot medium fill primer as their standard primer and low fill only for revealing low spots in a panel. This is due to the fact that since you need to scuff the primer to provide the mechanical adhesion for the paint, you might as well add enough material so that as you remove it it smooths the whole surface of the panel.

The problem with this technique is that it is very easy to "double shoot" a trouble area in a panel, willfully over-shooting the primer almost to the run / sag stage in the hopes of shooting once, and then sanding. Any panel shot in this manner needs at least 24 hours in a HEATED Booth in order to evaporate all that solvent carrier. If you let it sit overnight at room temperature, I will guarantee that the primer below is still not set. If you start sanding, because the top feels ok, you will very quickly note that you start picking up these little "boogers" (sorry, it's what they get called. Those of you who choose to re-read that last word several times...well.....geesh!)

Those little "boogers" are actually thin pieces of skin from the primer that are starting to clog your sandpaper and worse yet, cause the still uncured primer to mix with water or get dirty.

You're better off using a good etching primer with low fill. Shoot the car completely and shoot your NEXT coat with some compatible HIGH fill primer. This primer is designed to shoot plenty of sandable material in one coat and still cure overnight. It is more desireable to let it sit in a heated booth, but you can still work it within 24 hours.

Primer as it looses it's solvent "shrinks" or more accurately, looses the "sponginess", and just like a wet sponge, as it dries it maintains it's coverage but it isn't as thick. This now leaves the bonded material ready for sanding for smooth.

If you shoot the high fill, when it cures it will have smoothed over what 3 solid double coats of medium fill would have. This makes it very time consuming to sand out, but the results are that a panel that is ~wavy~ or just has a few "dingies" can actually be made to look smooth with this method.

Hopefully you didn't use anything less than 36 or 48 grit.

Hope this helps.

Enrique

[Datsun-Fever]

I have this attachment for my grinder, its sort of like hard cork, but it has the texture of one of those hard sea sponges, i think its for removing paint and not damaging metal, should i use this? thanks.

[Ed]

I always thought that removing paint could be done with a D/A and 60 grit without scratching or warping.

Enrique, how would you recommend removing or preping the body for a fresh paint job. As far as I know my car has been repainted only once.

[EScanlon]

There was a poll just a few days ago regarding this exact subject. I voted ALL OF THE ABOVE.

http://www.classiczcars.com/forums/showthread.php?s=&threadid=7832

Each paint job has it's particular background and therefore a "one-size-fits-all" approach to all of them is hard to define.

Many times the base paint / primer / bodywork is not garbage, and just needs to be worked to accept another coat of paint. Now I know that there are folks that immediately got turned off at that idea. They're of the "strip it clean" mindset. That also has it's benefits, and it's drawbacks.

Then there are the intermediate jobs.

Ok, if you don't want to read something long, back out now.

Grind: ONLY to remove BULK product such as bad bondo, rust, fibreglass or other THICK coatings. If using on rust care must be taken to ensure that you don't thin the metal out too much and / or warp it because of heat.

Sand: D/A Sander; this is one of the best method to reveal problems while still maintaining an easy to restore surface.

I use this as my primary method of initially working a car when I have not detected any major problems and we're doing a complete repaint. A D/A will very quickly cut through various layers of paints and do it gradually enough that you can actually SMOOTH the panel with some of the old material. This works best when you're only going to smooth, prime / fill and sand for final color.

Hand Sanding: If the car has come in virtually damage free, or the amount of damage is very slight, and we're going for a full repaint, then depending on the top coat color, either sand for primer base or sand for color reshoot. Granted any repairs should be done first.

Chemical Stripper: When there is a LOT of paint, Bondo, High Fill primer, etc. this stuff is the best. It will eat right through several layers of paint and bodywork QUICKLY. When you are looking to completely strip the panel and effect repairs REGARDLESS of what may have been done before (because you'll be redoing it). Although this can seem like a boon, sometimes it just ADDS work that needn't be done.

Biggest disadvantage of the stripper is that it will seep into any small crevace / seam / hole and lie in wait there for you to apply paint. Then it will eventually cause a bubble up. Only way to avoid this is to neutralize the stripper once you're finished. This may be a lacquer thinner wash (very dangerous) or copious amounts of water followed by air nozzle pressure drying. If you're worried about the seams, tape them up and stay away from them.

Torch and Scrape: If the panel has some lousy work that needs just that TORCHING.

NOTE: Bondo makes nasty fumes when burning, be careful. And make sure you protect other cars in the shop, it makes these fluffy charcoal fumes that solidify in the air, then they land on stuff and really REALLY make a mess.

Be aware that it WILL scorch your throat, you've been warned.

For that matter, I use a respirator and fan ventilation when the bondo needs to be "torched" and I try my damndest to NOT ignite the bondo. It will loosen it so you can scrape it off, just take care and don't try to take off too much in one scrape.

Sandblasting: Whether with sand, bead, or oxides is an EXCELLENT method. Biggest problem is trying to use more air or more aggressive media and causing damage. Remember, as you remove the paint, those areas that got cleared first are now being ... sandblasted! That can thin metal and the heat can warp it easier now. Again, sometimes it's the fastest and cleanest method. Interiors are a good place to NOT use stripper and instead sandblast. Biggest problem with that is to then have to vacuum every nook and cranny to remove the media.

Dipping: Probably the BEST method of removing EVERYTHING not welded or bolted to the car. This includes seam sealer, undercoating, bondo, plastic, rubber, unwanted neighborhood pets etc. Although this may seem desireable it is only if you're planning on removing factory panel welds and get into really REALLY inaccessible areas. (Think: How do I replace the seam sealer around the rear fender? That's how thoroughly it cleans stuff.)

There are various other processes that can also be done to a car after dipping. Electrozinc, phosphate, galvanized etc. All have their uses and advantages / problems.

BEST CASE SCENARIO:

Car arrives, showing obviously faded paint, a few rust bubbles in the lower rear of the front fenders, also on the rear fender lips; there are your typical bondo lillies in the hood, doors and roof. We're going for a complete repaint.

I'm not going to go into detail on whether or not to remove parts or the prepping the car for the work.

Faded paint indicates that it's been in the sun a LOT, and hasn't been properly waxed or cleaned regularly. If this were the only problem, then a simple wet sand to ensure smoothness and to properly feather out the bondo lillies and you're ready for either primer/sealer or another shot of paint.

The rust bubbles indicate rust coming up from below. Once you see bubbles it is a good chance that you will find holes. Holes means BIG rust spot on the other side. That must be addressed before you can do anything else.

In the front fenders, since they're relatively easy to remove, I would address the problem from the backside or inside of the fender. Once off the car, remove any undercoating and loose debris with a wire-wheel. Then if necessary use a light sandblast to determine how much rust is therel. If even before this you're encountered a lot of holes, even if tiny, you should cut and replace the section with new metal. That's the tried and true old school method.

Nowdays, with the difficulty of brazing / welding on repair patches, sometimes it's easier and more cost effective to use some of the super hardening compounds out there. We're not referring to bondo, but rather to fibreglass or POR/Power Mesh, or JB Weld with mesh screen. This does not replace the metal, nor does it strengthen it to what it was, but sometimes due to circumstances, most usually cost, it's the quickest and easiest method to repair those holes.

Other really cheap methods are the famous Bondo till you push it out the back; Speed tape (aluminum "scotch" tape or duct tape); newspaper, cardboard; and the famous rivet a piece of metal over the rust and bondo the outside till it's smooth again over the rivets.

The rear fender lips are a big problem. Depending on how deep and severe the rust is, it may be impossible to save without cutting and re-welding. That's the worst case scenario.

The best case scenario is that they're only paint chips that have rusted and bubbled the paint around it.

Unfortunately, if the seam sealer inside the fender failed or didn't stick properly, then you more than likely have rust between the various sets of sheetmetal that join up in there.

If that's the case then you need to ascertain just how deep and pervasive the damage is. A small grinder bit on a Dremel tool will make it easy to "dentist drill" the rust. You won't find all of it, but you're going to do something else for that. Only you can determine if you need a bigger drill grinder to eradicate what you can of the rust. This is why many times you'll see body men push in on the fenders with a metal probe. This area on just about ALL cars is a problem.

Once you've done the Dentist Drill routine, you will have opened up many holes and possibly a seam. At this time you either figure out how to effect repairs or how to replace the fender lip. I judge it by the amount of true lip left. If the lip is generally sound, but with some small holes / pits but no real tears, I'll heat the fender up with a torch and flow solid solder into the seams. You need to properly prep and "tin" the metal and neutralize it afterwards but the result is that you'll "cap" or seal the rust that has crept in between the metal layers. This method works when you can remove any old sealer (typically will burn off, but makes NASTY fumes) before you torch. When you torch you need to be careful to NOT heat the metal red-hot. Solder won't stick then. You need to heat it enough to allow the solder to flow and seep into the metal. Just like if you were "sweating" a copper pipe.

Another method of doing this is to seal it from the back-side with POR or another rust encapsulating product. Once sealed, then finish off the outside normally.

The bondo lillies are shrunk bondo on the surface of a panel that is now deeper than the paint around it. Also noticeable when someone has oversanded the blend area so that it's only the edge of the bondo that's lower than the center of the repair and the metal. When seen from the side they look just like water lillies just underwater, hence the name.

These are best taken care of by carefully D/A'ing the panel to reveal the low, then glaze and primer/sealer. In this scenario I wouldn't remove the prior bondo unless there were some good indications that it needed to be removed. That old bondo has now shrunk to it's final shape and will actually work better than new bondo that has yet to shrink. That's why you don't bondo on Friday to paint on Sunday.

The rest of the car would more than likely be wet-sanded only.

Hope this helps someone. Sorry for the length.

Enrique Scanlon

[Alfadog]

Sorry for the length? THANKYOU for hte length more like it!! I know who to contact if I want to do any painting...

[Ed]

Don't worry Enrique, I could read your stuff forever. I learn something new everytime.:classic: