undercoating or paint or chip guard

[Yan2947]

I could use some advice. I'm not a body guy. I need some help with undercoating or painting the underbody. I had tried to clean up the bottom by covering the factory (1986) thick rubber undercoating with paintable undercoating - bad choice - and then painting the paintable undercoating. Nope, didn't work. The paint just came off and the paintable undercoating remained soft. I pressure washed the paint off and most of the paintable undercoating. Now taking my time to remove the residue.

What should I do now?

1. wire wheel all the undercoating off, epoxy prime and paint or chip guard and paint?

2. can anything cover the factory undercoating and then paint (guards red). I would rather cover the factory undercoating - it would make life much easier and then paint the undercoating.

I have read a bunch of posts on the site and have not been able to get a good answer. Perhaps I missed the good post that would have covered and detailed this exact question.

[Monkey Wrench]

I spoke to a guy that used a pressurewasher that fed sand in the waterstream, he said he did that, presure washed it , then put a rust amalagamator, washed that then primer, maybe epoxy..

Ive been experimenting with small parts soaking them in washing soda and water with a car battery , and a hunk of iron, it removes al the paint and the riust quite well, leaves a blackened coating to scrub off before coating. I like the method but oding a whole car, well first youd need to build bsically a little swimming pool , Id learn more before attempting a project that big..

sandblasting , well its a dirty job and Im not clear how well it will remove the undercoat gunk. I would not open sandblast thigns unless you can get it into a suitable space as the grit is horrible. with water it may be less airborn. you may need trarps and cloth to contain the stuff.. thats how Idl clean the bits you have around that youll also want o do. Id suggest try that and start small and see how you like it. not much cost to that.

you might just try solvents and see what dissolves the coating you have. start with a common solvent or brush wash then go to more harsh chemicals only if you need.. some of that tar stuff is dissolvable in a basic solvent. If you can use chemicals instead of elbow grease it is a help. give it a shot of WD40 see if it can dissolve whats there if so maybe a solvent of some sort.

when you are at or finishing the paint stage and have finished whatever cleaning you might want , Id try to spray something inside frame areas and such where you cant reach.. there are suitable products for that..

Im interested in the topic of dunking the whole thing but ask others who have done so. Ive done lots of little parts with electrolysis, I like it, no harsh chemistry , a solution of washing soda you ll find it with the laundry soap, I used arm and hammer brand. I may use some baking soda and water on a rag for cleaning. Im looking for a good way to remove the blackened stuff..

I use a car battery and leave it on the charger so Im runing 12 VDC maybe some higher DC voltage speeds things. be careful not to electrocute yourself.. if you short things out accidentally you can wreck your charger or melt down the battery. maybe not bad to put a piece of plastic between I like using a tray for vegetabls with lots of holes in it for loose parts , to prevent that.. like an old plastic milk crate.. just something so parts cant; touch the electrodes and short out.


the proximity of the expendable iron rods affects how concentrated it works so you want to distribute them and I;d expect this not ot be a one stage deal.

with sandblasting you may heat up the base metal maybe causing hardening with water, it stays cool.

sandblasting and grinding , cleaning pads may remove good metal they arent; particular about what they remove, acids also eat the base metal. electrolysis acts only upon the rust.. a wire wheel may flick bits of metal wire so it has that danger and also it could close up pores over tiny rusty dibits. wear goggles and a face shield and watch the wire wheel is not run faster than desiged. you can create a circumstance where you look like a porcupine with spikes all over stuck into your coveralls and you certainly dont want to take chances of getting one of those in your eye.

disc sanding pads work well Id try a 5" angle grinder with a flap disk for the easy stuff the flat areas, maybe a stiff wire wheel on the angle grinder for the recessed areas.

sandblasting or an etch or sander, may help the paint bond by leaving a "hook" in the metal.

I dont think Im qualified to answer your question at any sort of expert level so maybe see what others say.. maybe therre is a place that can dip it and then you could just use money, money works! ;-)

looks like a fun project , I have a 66 volvo 122 that I have a lot of time and work into , its rusting away within the unibody frame parts and I would love to strip it down to do that level of work to the chassis.

I did what youare doing to a rusty trailer, half an old pickup, I pressure washed then used rust amalagmator, pressure washed again , painted, it worked well. lasted, rust did not reappear much even after 20 years in the weather. I wasnt being so fussy as you may want to be with that project

[Tony V]

If most of the factory undercoating has been removed, I’d go over the underside with a wire wheel to remove the residue. I’d then coat the pan with POR15. While it’s still tacky, spray a light coating of primer. Once everything is dry, you’re choice of finishes. Make sure you topcoat the POR15 before it dries. Paint won’t stick to dry POR15. Undercoating would be nice as it provides some sound deadening unless you’ve lined the interior.
Make sure to photo document the process. If you ever sell the car a buyer would like to know that the undercoating wasn’t applied to hide issues.
Tony

[Yan2947]

Thank you two for both of your responses. I cleaned the bottom at least a couple more times and then I sprayed either epoxy primer or single stage paint on the bottom to test it out and see how it adhered. I spoke at length with the tech guy from U-POL. He advised that I paint a few areas and test it out. If the epoxy primer adhered well, then Gravitex Plus overpaintable stone chip protection would work well. He also said if I just sprayed an area with color over the factory undercoating and it adhered well then I would know that the rubberized factory undercoating could most likely stay on the car and I can put gravitex on or just paint color over the undercoating. I believe he said that gravitex is a urethane based covering and it is not an asphalt or tar based undercoating like I had just previously done. He also said that raptor lining would work fine, but it would not be as forgiving as the gravitex. As the photo here shows, I cannot just spray red paint on the undercoating because there are areas that don’t have a smooth finish and it looks bad. The same goes for just epoxy primer and paint where I need more of a filler to cover some of the pressure washed factory undercoating. I think the plan is to do the following unless someone here has more knowledge and can give me advice. My thought is to epoxy prime everything and then put gravitex on and then single stage paint over that. Should I use single stage paint or 2K paint base clear. Not used to doing BASE clear. The only place there is rust is where the body shop put my Wide rear quarter panels on the passenger side and never covered it with anything after welding it on. It is just the one quarter panel and that is gonna be cut off and moved slightly forward about half an inch with a lot of metal work. So there is no reason to dip the car or electroplate anything. And I really don’t wanna take the undercoating off. It would be pretty simple for me to do on the bottom of the car and in the front suspension area but so much more work in the transmission area underneath. You just can’t get to everything in that area. Any thoughts?

[Dpmulvan]

Been there done that. I stripped the entire bottom with a HF pneumatic chisel and knotted wire wheels took me about 8 hours to do the whole thing. If you’re not stripping the whole thing I wouldn’t waste all that time and money on products especially at today’s prices. Seems like a daunting task but once you get the process down and get on a roll you’ll be done before you know it. Cars already on a rotisserie it’s a no brainer.

[Yan2947]

How did you strip behind the torsion tube where it’s really hard to get at?

[Yan2947]

And after stripping, what was your process?

[Yan2947]

I am taking at least the bottom center and front to bare metal. When does seam sealer go on? After epoxy prime I believe? Or when metal is exposed then epoxy priming?

[Yan2947]

Spent about nine hours straight with the wire wheel on a grinder taking the undercoating off the bottom center and front suspension area. I’m probably gonna leave the transmission engine area and epoxy prime it only and then paint instead of stripping it down because it would be a lot of work to get back there especially behind the torsion tubes. No rust in any way which is nice. I am exhausted. So my plan unless someone tells me differently will be to completely clean everything after rough sanding with red scotch bright the bare metal areas and I will probably scuff the undercoating in the back also. Then I will epoxy prime. Maybe two coats if someone tells me here to do two coats. Then I will put seam sealer where that needs to be. Waiting a couple hours that the epoxy primer says to wait before you top coat it and I will topcoat it with Gravitex gray and I will wait the time it tells me to wait or perhaps a day or so and then I will topcoat that with single stage guards red. I think that’s correct, but perhaps one of the great painters/body shop guys here will chime in. I assume I will put two coats of red single stage urethane down, correct?

[Monkey Wrench]

looks like you are doing a good job and i thik we all appreciate how much work it is just getting the car to that stage and then reassembly but it should look nice.

part of the reasom why lots dot like undercoat is becuase once the rust gets going between the metal and coating it creeps along using apaillary action to work its way in..

Ive been using the rust amalgamator , you have to wash it after application before painting bu tI think that might help especially in any rusty areas that are out of reach.

my van developed a hole in the floor due to a windshield leak, the water got between the ruber mats and there is sound insulation that is absorbant.. I cleaned it up as best I could and then put the rust amalgamator a couple times. rust check or rust mort or there are other suppliers. I checked price locally ont he weeend about 100 CDn ofr a gallon or you can buy coffee cup sized bottles.

not wanting to go to the extend of welding I cleaned and used rust amalgamator then i painted it wit a 2 part epoxy coating , laid fiberglass and more epoxy. let it knoit together. I did also add a stainless steel plate bolted in underneath,

the stainless might cause electrolytic reactions.. posibly..

in the areas you cleaned they look reday, Id find out if maybe a etch could help the bond or maybe por 15 has that , possibly.. I know it can bond well to a surface coat of rust, if the rust is layered nothign will help you have to get the flakey stuff off,or capillary action will take water there.

a body shop supplier will have an etch product you can brush on and wash off to cleean the metal chemically.. whenever I repaint stuff I like to use a brush and acetone the acetone breaks grease and tends to dull any paint and makes a better bond than if it is smeared by a polluted wire wheel.. i brush that on then dry down with clean rags,, if the rags are dirty with grease or old underrcoat then Idl keep going until I feel its astringent.


the rist amalgamator :
i dont gind I need a lot of it.
what it does it combines wiht rust thats left and turns it black and makes it accept the paint better than just paint on rust.

some internal areas impossible to clean Id use it there and then maybe a spray, rust check makes a product but I don't work for them. a sticky substance that maybe never dries, a bit like beeswax maybe. it may have the ability to creep which is good inside a box where you can't access..

i bought some kits long ago made by bondo,, the kits come with plastic plugs, you can dril l holes to acces and then plug them,
you can spray it around into holes ec with a spray can and a little hose to dispurse it where you cant see rf clean.

If you are using por 15 paint its good stuff for that too.

a place where you can go all wrong is if you coat over something that is still offgassing and not cured, then the underlying area is still releasing vapors while covered by some other coating and that can cause bubbling between.

If I paint stuff with a rattle can that is enamal Ill give it a quick first coat, then 10 mins later do a heavier coat whoile the first is not yet dry, then let it harden, scuff and do more coats. the first coat makes a bond , its not thick enough to run or cover properly, the second coat can then be a bit heavier and it will be less likely to run as it has kind of a sticky surface to bond to and it is compatible since its not really dry or cured yet. leave overnight at that point, you can do more coats after offgasisng is complete. If you go back in 1 hour with another heavy coat then youll see a problem.





If I go back in an hour and do a good coat, then Ill see the ofgassing issue as the first layer wont meld wiht the other layer it will lie overtop and then the paint is offgassing underneath. thats avoidable, the solution is more dry time between coats.

epoxy dries by chemical reaction acrylic enamal dries by offgassing its solvents. I dont have experience with acrylic.


I am by no means an autobody pro. what ive done over the years , from my experiences if I cleaned it well and then applied a real two part epoxy it has not rusted after. Imron is good, it does stink.

wearing a good chemical resperator that fits you is worthwhile you can add a dust filter for the airborne solids. in industry a fit test is necessary, if you have a beard an air fed hood is an option.

[Dpmulvan]

Originally Posted by Yan2947

How did you strip behind the torsion tube where it’s really hard to get at?

Used pneumatic chisel, various rotary tools,razor blades and knotted wheels for the most part. Most of the questions your asking answers can be found in TDS ( technical data sheets) available on the website of the products. I put a coat of epoxy let flash put another coat let flash and then applied gravitex. TDS will tell you the window for topcoating. Not sure why you’re painting the entire bottom? If you insist on having the bottom red I would use white bedliner with urethane tint to get your color but the trade off is bedliner is harder and might chip easier. Don’t believe you can tint gravitex but I know you can tint bedliner. And don’t use por15.

[Yan2947]

Originally Posted by Dpmulvan

Used pneumatic chisel, various rotary tools,razor blades and knotted wheels for the most part. Most of the questions your asking answers can be found in TDS ( technical data sheets) available on the website of the products. I put a coat of epoxy let flash put another coat let flash and then applied gravitex. TDS will tell you the window for topcoating. Not sure why you’re painting the entire bottom? If you insist on having the bottom red I would use white bedliner with urethane tint to get your color but the trade off is bedliner is harder and might chip easier. Don’t believe you can tint gravitex but I know you can tint bedliner. And don’t use por15.

Thanks for the detail. I did get to reading all of the TDS'S for the various products. I'm using the gray Gravitex undercoating then top coating with the guards red. There had been so much overspray from the body shop that worked on the car that the bottom was terrible. Even the tires got overspray. I decided to clean it up. I was told that the gravitex is paintable. People swear by it. I realize a chip is going to expose the gray most likely. Hopefully, I won't have to re-do anything. I'm going to seam sealer after the two coats of epoxy primer then gravitex then single stage paint.

[Monkey Wrench]

when cleaning stuff for paint, a thing to keep in mind is that some stuff is water soluble, some is soluble in a solvents. stuff that is soluble in solvent is not necessarily water soluble or the reverse.

so beacues of that its sometimes good to use both, alternate, there are also water miscible solvents.

when analizing the underlying stuff, you can experiment with different solvents, for example you can try alcohol or paint thinnner or acetone or go into paint stripper and other chemicals.

as an example tar like compounds will probably dissolve in solvents and wont bond well to pait although you can spray overtop and not see much difference. epoxy is very resistant to most chemicals. I think if you are putting epoxy down and getting it into seams you dont really need the seam sealer but maybe if there were some gaps to fill it won't harm anything

as an example maybe you have a piece that is spot welded but there are some gaps you dojt want ot take the seam apart. you might stuff seam sealer into the crack with a putty knife to try to fill the small gap and stop capillary action from letting water creep in and causing rust.
a lot of vehicles nver were very well protected in certain areas if at all , inside rocker panels or where the metal is folded and brought together near fender lips can be areas that never were protected very well and then you can get the rust creeping through from the backside where paint never was protecting it well.

where the body shop did work and failed to seal well after welding , sometimes paint can be burned off in unseen areas and then it will return as an expensive or hard to fix issue.

if metal is in the process of rusting through from the backside you can't solve that by only attacking only the front side.

even if its hard to clean or see then its still likely possible to put some sort of coating to try to slow down to slow the process,

it happens often where people paint cars and make them look very nice , only to rust from within and bubble out within a few years. basically spoiling all their hard work.

the rust works its way through from the reverse side where they paid less attentpon due to it being basically an unseen area. By the time bubbling is noticed on the outside, the reverse side is rusty and thin, thats hard to fix.

cars were not intended to last 50 years. obviously with care to these details they can but protecting is a lot easier than replacing metal.

I spoke ot a workmate, a mechanic who said he went to germany , to the porsche factory around the 944's production time and that they has one on display it was unpainted and displayed out in the open like that to show it's ability to resist rust, I guess enhancing the fact that they had used galvanization. would anyone know more about this display car?

Im not clear om what was or wasn't galvanized originally.
galvanization is zinc, boats often use zink electrodes, it has low nobility. here is a list of the "galvanic series"

https://en.wikipedia.org/wiki/Galvanic_series

the Porschealso has a lot of alunimum which is also low on the scale, as different metals are used in combination corrosion can be influenced by the proximity of dissimilar metals.

with boats they often use expendable electrodes made of zinc blocks the idea is that since zinc has low nobility it gets attacked first this helps the duration of other boat parts.like the motor or leg. I often wonder if attaching such an expendable electrode to a car could help? or would it do nothing? not being in the water?

I fixed a samsung washer, the drum is made of stainless, in benind this drum there is a "spider," its a buig hunk of pot metal shaped like a peace sign, it attaches the drive axle to the drum, the axle is cast into it.
well the spider breaks down, mine was all broken and looked a lot like sand bonded together and crumbling to dust , the drum came loose, I took the time ot fix it.

that wsas a good example of corrosion caused by dissimilar metals. There was a consumer class action suit becaues people unknowingly paid lots for high end machines and the manufacturer was well aware it was destroying them by this known and very predictable reaction.

I'm interested in learning more about the effects of corrosion by dissimilar metals as related to the Porshe because has a lot of alunimum and also the galvanized coating. Iromn in th proximity of aluminum causes an electolytic reaction.
mine has a lot of unsightly aluminum corrosion. are there good ways to clean it up?

I got some free plastic driums from an autobidy supply place along with them I got some car wax etc one had an aluminum cleaner, maybe that would work well. the bodyshop supplier bought it in drums and probably sells it in smaller quantities. maybe that would be goood for cleaningf transmissions engine parts, wheels etc?

ive been experimenting with some aluminum wheel cleaners trying hard to get off brake dust, some is sort of an acid, it works but takes some work for sure to get those old layers off and make them shiny again. I tried all sorts of solvents, the stiuff is tenacious.. one thing that did seem to work was "oil lift" its used to clean garage floors. maybe toilet cleaner, somewhat. even acetone wont dissolve it.

some paints are incompatible , for example layering acrilic enamal and laquer can result if problems of underlying finishes lifting and bubbling, the wrong combination can make quite a bubbly mess. a lot of undercoat was laquer based at one time anyway.

with furnature, if a person has an antique and doesnt; know the finish often they will rtry alcohol, alcohol will dissolve shellac.

laquer is a completely different animal ! with acrylic enamal or epoxy or many modern finishes each layer solidifies never to be redissolved. not so with laquer. if laquer iis put overtop of existing laquer it "melts into" the existing finish. laquer generally dries fast, it can be a good paint but not as chip resistant as some other paints.

with ooder actrylic enamal it was possible to just sand and put more and get a good bond and a new finish no clearcoat was needed. with tbasecoat clearcoat finishes its a bit diferent and I think I could lean more on all this modern chemical technology.

half my car seems to have a basecoat clearcoat finish , I think the roof and one side is still just acrylic enamal ,, I think just acrylic enamal was the original guards red finish. the acryulic enamal and roof is a bit faded. ive been cut polishing a bit ,by hand, maybe not biting in far enough , I did it by hand twice, I shoudl probably get a polisher and some differnet grits of polish. maybe I can get the faded stuff off and apply a clearcoat?

I found that when I triued spraying laquer to refinish furnature, (Antique radio restorations) I had a rather surprising learning curve beceuse of the laquer dissolving underlying laquer. I was used to painting things like cars with acrylic enamal, where a susequet layer would not melt into the underlying layers. I did not at first realize this was the case. although you are nto using laquer I thought it worth mentioning as it wasn't immediately apparent to me.

laquer probably is not such a main go- to for most auto applications these days but it can be mixed to match colors. I once painted a car along with an experienced bodyman. we used acrylic enamal way back then. he had me order a quart of laquer as well as the paint, with the same mix. We painted all the door jambs with that and then we could close the doors the same day because it dries fast.. we had limited booth time and it turned out to be good guidance.

I think some liked it for antique cars as it was easier to maintain , Ive never paited a whole car with it. it does chip easier than some paints. maybe there are benefits to using it. I think in moast applicatioins body shops moved to less volatile paints for health , enviro concerns and availability.

with my antiques it is possible to strip and refinish but many dont want o be too destructivem , they want o repair the existing finsh Ill iuse an amalgumator product to help bridge that bond In that case the objective isnt; to make it look showroom new and shiny it is to make it look like it was cared for and never worked on. this means preserving its wear and patina, rather than just refinishing it.


I found that if I was doing work out in my yard the newer chemicals made way less of a stink and I don't want my neighbors complaing about the solvent fumes. I could benefit form more knowledge of these modern clearcoats etc. I think I could paint a fender outside but if its acrilic enamal or epoxy I could get a complaint. the modern basecoat clearcoat is good that way.

epoxy is hard to chip once down you can bounce a wrench of it, other finishes are harder and can chip. If you have even a thin layer of a tar like substance the bond won't be any stronger than the tar bond. it will still dry and look ok.

the project is looking great! I hope I didn't write too much or confuse your post.

[Yan2947]

You definitely wrote a book, but I thank you for all your details.

[Yan2947]

Thank you all for the help and really great details of how actually to accomplish this. I took everything down to bare metal except for the transmission area and inner fenders and rear quarters and engine area. I used Zep industrial purple to clean and decrease everything after using mostly a knotty wire wheel to strip the rubber undercoating from the factory. I also had to use a lot of smaller wire wheels to clean up. I followed the TDS on each paint suppliers website and used off brands all that I received from a local autobody supplier. The TDS gave me pressure at the gun, flash times between coats (usually around 15 to 30 minutes), top coat times which was pretty quick except the Gravitex which said 4 to 6 hours but their tech rep said to wait 6 hours which got me finishing up at 130am last night. I left the factory undercoating under the tranny area because it would have been a lot of work to get in there with all the wire/hose tabs and behind the torsion tub, etc. I did not remove anything from the inner fenders and inner rear quarter area. Just cleaned with the zep industrial and then prep wax and grease remover and then painted with a single stage 2K urethane. I epoxy primed everything else which included the engine area, tranny tunnel area, the main center under the car which was stripped to bare metal along with the front suspension area also stripped to bare metal. After priming I used seam sealer to brush the 14 plug areas on the bottom of the car, the edges at the bottom of the car and a bunch of other areas that would have had seam sealer including the control arm area. I waited the 30 minutes and then applied a gray Gravitex from UPOL. Their tech rep was great and patient. After the Gravitex I had to wait 6 hours to top coat the guards red color except where I didn't use Gravitex like the engine area and inner fenders/rear quarters. Those I painted two coats of paint. At midnight I painted the remainder.

What I was told by some of the really knowledgeable people here is that as long as the original undercoating was in good shape I could just clean it up and scuff it a little and then paint. I did do that to freshen up a few places and it worked out well. Hopefully the paint will hold forever. Seems to be rock solid.
Hope this helps someone else.

[Dpmulvan]

Nice job!

[Monkey Wrench]

looking great! you wont regret the time spent.

[962porsche]

looks like you did a good job restoring the underside of the chassis.

for sure if the chip / stone guard on the car is still in good condition there is no good reason to strip it off to bare metal. you would be spending long hours time and money to do it for no gain.

the undersides of the panels and chassis was not paint from the factory. the paint the gets on those areas is just overspray.

[Yan2947]

Originally Posted by 962porsche

looks like you did a good job restoring the underside of the chassis.

for sure if the chip / stone guard on the car is still in good condition there is no good reason to strip it off to bare metal. you would be spending long hours time and money to do it for no gain.

the undersides of the panels and chassis was not paint from the factory. the paint the gets on those areas is just overspray.

Thank you for all your help! The main bottom center and the front was pretty easy to take off with the knotty wire wheel. And the center part was definitely more fibrous and would not hold the paint very well because I over pressure washed it and it started to deteriorate. You can see in the earlier photos up above where I did some paint samples and when you inspected it closely whether primed or painted it did not look right. Had I just cleaned it with purple industrial zep and degreaser de waxer prep, I could’ve just painted it. Epoxy primer was easy to apply and did cover up some areas that had metal exposure. But I agree if it was all good undercoating just paint with a good single stage 2K paint. Thanks again!

[Okiikee911s]

This is looking great! You definitely wont regret the time spent.