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Painting engine bay and wheel wells

Hello,
I'm sure this question has been answered here before, but I have been searching this forum for a while and can't find a consistent response.

I would like to repaint the engine bay and wheel wells on my 911. The engine is out and the fenders and suspension are off the car, so I have easy access to everything.

For this job I would like to simply paint over the existing paint. This is not a color change, and the color is silver. From what I have read so far, for this type of job it is recommended that I:
  1. Remove glue residue on firewall from foam pad
  2. Thoroughly clean/degrease the existing paint
  3. Scuff existing paint surface with Scotch-Brite Red
  4. Apply epoxy primer coat ???
  5. Apply First stage color
  6. Apply Second stage clear coat

What I am not sure about is the epoxy primer at Step 4. I don't see too many people including this in their process. Would applying the primer over the old paint be a bad idea? Would it help with adhesion?

There are also a few areas that I had to take down to metal. For those areas, I plan to first:
  1. Etch and zinc coat the metal using POR15 "Prep and Ready"
  2. Apply a Self-Etching Primer ???
  3. Apply Wurth chip-guard
  4. Continue from step 4 above (Epoxy primer)

Does this sound correct? I'm not sure if the self-etching primer is redundant if I use the "Prep & Ready" first.

I can post pictures of the existing paint if that would help.

Thanks for any help.
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Old 09-18-2012, 10:21 PM
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There are others much more experienced than myself to answer this but if it helps I followed the steps you have outlined here.

For the first process I was advised to use primer but I only did a light couple of coats. The paint supplier told me that primer would give better adhesion.

With the second process I would also use primer. The metal ready product from Por15 will assist to 'galvanize'' the bare metal but it is not a long term solution to protect against corrosion. The primer will help to ensure that rust is not an issue down the track. A sealer may also help, but this is where the experts can confirm. The Wurth SKS is water based and I believe it is not a perfect barrier to moisture so applying to bare metal without some sort of protective layer would not be advised.

I think the trick here is to go light with your coatings. It will look better and more original plus will most likely be longer lasting.

I hope this helps.
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Old 09-19-2012, 04:08 AM
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If it's just the engine bay and trunk, I'd be inclided to do a hard-core degrease and then scuff it down with #600 followed by a prepsol product. If the paint is otherwise in good condition, I'd shoot directly over top as it is not a colour change.

That's just me
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Old 09-19-2012, 06:28 PM
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Thanks for the responses.
To prime (over paint) or not to prime - that seems to be the question. In my searches preparing for this project, this is the one question for which I could not find a definitive answer.

So my question really becomes, how would the epoxy primer over the existing paint affect the adhesion of the color coat?

a. Decrease adhesion
b. Neutral (neither help nor hurt adhesion)
c. Increase adhesion

Something else to consider: Would the primer need to be sanded prior to painting? Because if so, then the answers is No Primer, because there is no easy way to sand the irregular surface from the SKS.

Also, since the areas taken down to bare metal will have unpainted SKS on them, I assume at least these areas will need to be epoxy primed? And if I'm priming them, would I be better off just doing everything?

Thanks again
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Old 09-19-2012, 07:39 PM
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Hi Frank

The SKS texture is the reason I was suggesting just cleaning well and keying the surface to take another coat. I'd even suggest using a red scotchbrite pad rather than paper to try and keep the texture. The modern paints really are very good at "sticking" so long as there are no contaminates (oils/silicones) on the substrate they're being sprayed onto.

FWIW, the SKS is in effect a primer as well. It is the last process and product layed down before top-coats on a full respray. So if you find your engine bay or trunk is really messy with dings and gouges, you may care to put down a layer of SKS over the prepared engine bay as a primer before paint.
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Old 09-19-2012, 11:46 PM
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Watching this closely as I am about to start doing the same thing.
What is SKS? the rubbery stone protection stuff?
If so, John, do you have a brand name I can look for in Aus?
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Old 09-20-2012, 04:52 AM
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You don't need to prime over the top of SKS, but I would be keen to prime under it, especially over bare metal or repaired surfaces.

Bill - SKS is a water based stone guard product made by Wurth. You can buy it locally. You need a special gun which they also sell, which will give you the right texture. SKS is available in black or grey.
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Old 09-20-2012, 05:07 AM
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Yes, I agree with priming under the water based SKS.

Bill, an alternative to Wurth (and what I used) is Upol "Gravitex", it's solvent based and can go over small patches of bare metal (but I'd prime). Comes in white, black and a premix grey - but you can use any combination to get the right tone. And I've since found out you can get white Gravitex tinted to suit... I used two containers to do the engine bay (and had some left over). The other good thing about the Upol is the container is compatible with the generic (cheap) underbody guns you can buy (and dispose of) at Supercheap.
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Old 09-20-2012, 04:26 PM
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Ok, so now one final (probably not) question. In one area of the engine bay I need to fill a dent. I will take the dented area down to bare metal, but then I am not sure about the next layer in the process.

IIRC, I read to always apply the plastic filler directly to the metal - is this correct? That is, do not use self-etching primer on the bare metal first and then apply the filler over the primer?

So when plastic filler is used, is this the correct stacking order:
  1. Metal
  2. Plastic Filler
  3. Epoxy Primer
  4. Wurth SKS
  5. Color Coat
  6. Clear Coat

Thanks for all the help everyone.
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Old 09-20-2012, 09:55 PM
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D911SC, John;

When you suggest priming under the SKS, is the self-etching primer over the bare metal sufficient, or would you suggest a layer of epoxy primer as well before the SKS?

Thanks,
Frank
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Old 09-20-2012, 10:00 PM
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Hi Frank

There's just so many variables, products and opinions

Let me say this, there is no reason to remove good existing paint - so dont! The process I used for my full resto which was bare metal (because of major repairs) was to put a layer of epoxy down over all the bare metal and then apply modern filler which doesn't have to go direct to metal (DTM), followed by primers and top coats.

I'm adamant that schutz can go on over properly sanded topcoats that are in good condition. If in doubt it doesn't hurt to use a primer layer in between.

If you have a ding in the engine bay, but have good paint, I'd scuff it back to metal with #80 grit to key the surface. It's an age old discussion epoxy then filler or DTM filler and primer - I like epoxy first to seal the metal then put your filler on and let it set. Sand and sculpt and finish it with #400. Then primer. Top coats can go on directly over the schutz, but a light coat of primer in between won't hurt either. Also primer can go directly over epoxy without sanding if you do it within the "window" - read product directions.
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Old 09-21-2012, 12:03 AM
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John,

I have two questions based on your response:

You mention that you like to "epoxy first to seal the metal...". I had planned to use self-etching primer whenever I applied primer DTM. Is epoxy primer also acceptable DTM (or is this another area of debate)?

You also mention "primer can go directly over epoxy without sanding...". When you mentioned "epoxy" in the past, I thought you were referring to "epoxy primer". If so, I'm now confused about the use of primer over primer.

Thanks again. I would like to get to the shop this weekend to start picking up supplies, I just need to know what to get. Then, of course, I haven't even started asking questions about paint types yet. There appear to be quite a few opinions on that topic .

-Frank
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Old 09-21-2012, 07:46 PM
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Hi Frank

Etch primers and epoxies are different from each other, but it's a preference thing. The main thing to know is that epoxy is waterproof and primer is not. So by laying epoxy you seal the metal from moisture and further rust which gives you all the time you need to work through repairs and restoration. This is a big advantage over primer when you live in tropical or moist climates. I work my filler over the top of the epoxy as well.

There are etch primers (containing chromate) which can go direct to the metal, and epoxies which by nature stick like mud to a blanket. Epoxies are a different chemical configuration that once dry are incredibly tough and robust - to paint over the top requires the surface to be sanded and keyed; but there is a period of time that you can lay a layer of 2-pack build primer over the top of the drying epoxy and you get a great chemical bond and don't have to sand. With epoxy and primer layers you have a great foundation for top coats.
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Old 09-22-2012, 03:59 AM
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Hi John,

Ok, so researching this a little further, I've found that there are (at least) four types of primers that I might need to be aware of for the work that I am doing:
  • Self-Etching
  • Urethane
  • Epoxy
  • High-Build

I also saw weld-thru and flexible, but I don't believe these apply to my job.

When you mentioned the use of primer over epoxy, were you referring to the use of a High-Build primer over an Epoxy primer? Same question about primer over SKS.

If I choose to primer over the old paint, would it be best to user the High-Build Primer, or Epoxy Primer? Are there applications where a Self-Etching is superior to Epoxy primer? And when is Urethane primer used?

Sorry for all the questions. If you know of a good website that explains all this (so I don't have to keep bothering you), please let me know. In the meantime, I will continue researching.

-Frank
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Last edited by frankc; 09-22-2012 at 12:29 PM..
Old 09-22-2012, 12:24 PM
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Epoxy primer is the best for sealing and preserving bare metal projects. High build is the best for block sanding the car to straighten out the sight lines. When all is finished, you use a sealer over and any all of it before the paint.

You can recoat expoxy w/o sanding within a time window. Otherwise it has to be scuffed and cleaned. Sealers are usually applied about an hour before base coat.

You have to read the directions. Any auto paint store, online store or website should be able to give you the sequence.

Most auto type fillers are polyester based. They work perfectly over scuffed epoxy and HB primer which is also polyester based.

In the engine bay, I would take more liberties unless this is a show car. Factories don't make a big deal out of undercar finish, it's just there to be the same color of the body and to protect. For non color changes of trunks and engine compartments I will use a clear sealer over a meticulously cleaned surface and spray away with your body paint.

If you can get your supplier to mix the same color in a less expensive single stage paint, that will be fine for the underhood applications.
Old 09-22-2012, 01:25 PM
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Zeke,

Thanks for the tip on using a single-stage paint. Will the single-stage be less glossy than two-stage? I really didn't want a high-gloss finish in these areas anyway, so perhaps single-stage would be preferred. Are metallics available in single-stage?

And thanks for letting me know about the sealer. The ones I have found so far are referred to as primer/sealers., but they do not list the color - are all primers clear?

Btw, here is a good site I have found that explains some of the terminology and processes used in automotive painting:

Types of Car Paint | Types of Auto Paint | Which Car Paint to Buy | Best Car Paint

-Frank
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Old 09-23-2012, 09:36 PM
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After all the nasty stuff I've been reading about isocyanates, I'm wondering what type of respirator I would need for doing this type and volume of paint work. Protecting my health is paramount to me (my other hobby is Ironman competitions), so I assume a supplied air respirator is the way to go? Is the Hobby Air product acceptable? Should I consider a water-based paint and avoid some of the hazards?

Then I need to determine if my compressor is adequate for the job. And it does not seem to be very easy to find a local distributor for BASF or PPG products that will sell to the public.

I'm starting to come full circle on this task. At first I thought I did not have the equipment and facilities to do the painting myself. Then after reading all the threads here about the folks who have successfully painted at home, the task did not seem too daunting. But now that I starting looking into the details and logistics of acquiring the materials, choosing a paint "system" from one of the various manufacturers, evaluating my existing compressor, purchasing a respiration system and paint suit, paint gun, etc., I'm beginning to wonder if I would really be saving much money over having the areas painted by a shop.

Of course getting the car to a shop is a problem since it is not a roller, so I would have to make a dolly for it. I did talk to a restoration shop today to get some estimates on doing some small sheet metal repair on the left fender (I took the fender with me to the shop). The shop has a trailer I could use to get the car there if necessary.

One other item I forgot about is that I purchased a euro rear bumper for my car that needs to be painted. I did not plan to paint the bumper myself anyway since it is a "topside" surface. I will likely have the rocker covers refinished as well. Given this, there may be some economies of scale that work in my favor to have the shop do all the work instead of only the sheet metal repair, and painting the bumper & rockers.

Any words of wisdom?
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Old 09-26-2012, 09:47 PM
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Btw, here is another good site I have found for paint and body repair:

Autobodystore Forums
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Old 09-26-2012, 09:49 PM
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Frank - If you do all the prep (part removal, cleaning, sanding), a shop might give you a reasonable price to paint. Might be worth it if this is a one time deal. The trick is to find a place that doesn't consider what you want a hassle and make it as easy as possible for them to do their job. Remember when you're talking to them, they're at work so be respectful of their time. Ask them up front what makes the best tip (beer, ect) to say thank you and have it ready when you pick up the car. Also ask if cash vs check or credit makes a difference to them. Sometimes it matters.
Old 10-02-2012, 10:18 AM
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