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How best to remove paint coat from undercoat/chipguard

Well, I made the decision not to plastic blast my '89 Carrera project car as it is totally rust free with the only paint issue being severely checked clear coat.

This car is untouched paintwise, all original factory paint an coatings with no repair, so I am just gently sanding off the paint to bring it down to the factory primer layer, which I will then seal and finish as per normal, using Glasurit products.

Only real question I have is how can I remove the paint coating from the underside of the car. Ideally I would like some sort of grinding process that takes the blue paint off, leaving a base of factory undercoat that I can then recoat with chipguard and then repaint in its new colour (Signal Orange).

I have been checking the Wurth site and a few others, lots of fancy grinding/rubbing/bristle disks and the like, but in all cases I worry about them loading up with undercoat and being useless after doing 1 square foot.

Anyone have any favourites in this space or do I just go with my regular wire brush on my small grinder and just be careful?

Thanks in advance,

Dennis

Old 02-09-2017, 09:18 AM
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So you're doing a colour change? I assume you'll strip the topside with stripper?

You might re-think the need to strip the stonegaurd, at least on the entire car - depends how far you want to go. You could paint the blue over with the orange after cleaning it well with lacquer thinner and a brush. The blue is likely pretty thin in most places.

Of course in the places you do want to strip you are on the right track.

I've had good luck with the wire brush on the 4" grinder. You'll need the knotted/wound kind, and you might go through a few of them. Can Tire has them in a few diameters, and the smallest is handy for some of the tight spots. Messy and noisy.

If you are careful you can leave the factory applied electrostatic primer (black) behind. In the spots you break through that you'll see the galvanizing but you won't remove is all until you press even harder.

Even if you remove all the galvanizing via media blast, it's still going to remain where it's doing the most good, in the places you can't get at or see.
Old 02-10-2017, 05:02 AM
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If I understand your question correctly, you could try using the 3M/Scotch-Brite bristle disks - impregnated with abrasive media. Depending on the stiffness chosen, it could be a good option for prepping the undercoating without doing much damage to it. Minimal pressure, slow speed, and don't linger in one spot - it'll melt and smear the PVC undercoating. You may not get it all but, it should abrade the remaining paint sufficiently. And as Jonny said, it likely wont be very thick.

I used the radial version of the bristle disk for removing a flaking repaint from the undercoating on the underside of a short hood. It worked rather well without affecting the texture.

Alternately, could try Scotch-Brite pads on a DA sander (or similar) if you're happy just abrading the surface well enough for paint adhesion.

The only reason I see to try removing all traces of paint is that you may see the odd blue stone chip down the road.

Before you start, do your darnedest to remove all traces of dirt, grease, etc so it doesn't get ground-in and cause problems. I've used Castrol Super Clean and a stiff plastic bristle scrub brush, power washer, etc. with good results. Followed up with wax and grease remover.

I believe the undercoating had less texture as the years went on but, if you need to repair some spots, here is some good info from DarrylID's site ('66 912):

DarrylD's Porsche 912 Project Page - Phase 9: Front & Rear Floor Panel Replacement

Let us know what you end up doing.

Tim K
Old 02-10-2017, 05:41 PM
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I tried the bristle discs and they worked to a degree...but basically they quickly melt the undercoat and then blend in the paint particles so I ended up with an "off blue" undercoat.

I will try a coarser disk to see if that works better, but so far no joy. I may just have it C02 blasted as they can take it off layer by layer.

Dennis
Old 02-22-2017, 02:02 PM
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Quote:
Originally Posted by Iciclehead View Post
I tried the bristle discs and they worked to a degree...but basically they quickly melt the undercoat
Try some Jasco paint remover on the underbody paint.

From my experience, it reacts with the top layer and leaves the next layer down pretty strong.

I would put it on and walk away until it dries. If you try wiping off when wet there will still be active remover and it will chew on the schutz stuff.

I don't think this is a common procedure. I am assuming you want as much "factory" to remain on the car as possible. I like the spirit but I like just painting the same paint over the factory underbody paint in close to the same intensity. You are aware it varies.

I do know that the base black/dark gray primer is absolutely bad ass. You cannot cut it with the JASCO. There is a valid argument for stripping the top layers if the factory primer is impervious to the stuff. Stripping is so damned clean.

I stripped my driver's rear quarter only. That is my statistical mass of experience. The black primer was on that panel.
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Old 02-24-2017, 11:41 AM
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There isn't any one way or easy way to do what you want. I would be very cautious of using strippers as I think you will find they will damage the undercoating and could cause an adhesion issue. If you must remove the paint layer I would suggest a wire wheel to gently remove the paint with as little damage to the shutz as possible. Of course realize you will remove some of the shutz/undercoat during this process. It is inevitable due to the texture. The original Wurth product is no longer available in formulation or color so take that into consideration. If you are going to attempt to match the OEM product you will need to custom formulate it.

I removed the OEM undercoating on my car chasing rust that mostly didn't exist. I replicated the Wurth shutz by tinting white Upol Gravatex. You can see my thread here if you like. : http://forums.pelicanparts.com/paint-bodywork-discussion-forum/939550-shutz-color-match.html I did find that the Upol seems to be harder and less rubbery than the OEM shutz. It is also porous I guess is the best description. What I mean by that is when I attempted to top coat it there were little pin holes. In order to combat this, I had some Glasurit 22 tinted to match the undercoating color to seal the undercoat prior to top coating.

Old 02-26-2017, 04:39 AM
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Quote:
Originally Posted by Iciclehead View Post
Well, I made the decision not to plastic blast my '89 Carrera project car as it is totally rust free with the only paint issue being severely checked clear coat.

Only real question I have is how can I remove the paint coating from the underside of the car. Ideally I would like some sort of grinding process that takes the blue paint off, leaving a base of factory undercoat that I can then recoat with chipguard and then repaint in its new colour (Signal Orange).

Thanks in advance,

Dennis
Sounds like you're a gluttin for punishment with what you want to do.

Based on the above, and considering the car is a later model with o real damage to the original undercoat. I would recommend that you first heavily clean with a solvent, heavy nylon bristle brush that will get in the nooks and crannies.. then pressure wash. Once dry, scuff the surface down with a red scuff pad and some prep-sol. After which I'd scuff again with red pad and denatured alcohol and rinse with the pressure washer. Your now ready to coat with a sealer, or paint.. single stage enamel is what I like for the bottom. If you use the sealer you don't have to heavily coat it.. I like to just mist it on, and give it a light scuff before paint.

If you want to remove factory undercoating.. use heat and a scraper, if done right it'll roll right off. Then you follow-up with the wire wheels etc.. to get the small places you missed.
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Old 02-26-2017, 10:04 AM
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Nice work drcoastline!

Lot of effort in that project, especially with attempting to duplicate the factory color and texture.
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Old 02-26-2017, 10:06 AM
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Thanks Onboost,

A lot of work for nothing. I wouldn't do it again I can tell you that. I had some minor rust around the battery tray. A few small spots where the floor pans meet the front tub in the foot well, a dime size spot at the pedal cluster. Some well intentioned persons made comments that if there is rust there it could be everywhere including under the fuel tank support. So that is how I went down this slippery slope. It was one of those while I'm here processes.

Of course it did give me the opportunity to modify the fuel tank and rebuild the suspension.

Old 02-27-2017, 03:07 AM
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