How to Restore an Exhaust Manifold
While headers may offer more performance, nothing fits a specific car like the stock cast iron exhaust manifolds, and when the car is restored or original, they are necessary. The problem with cast iron, especially exhaust manifolds, is that it rusts. The constant hot-cold cycling creates a lot of moisture, which causes rust on the cast iron, wrecking havoc on their appearance. The typical restoration practice involves cleaning and painting.
Painting exhaust manifolds has its own set of problems. If the manifolds are not perfectly clean, the paint won’t stick and flakes off. Even if they are sandblasted and ultra-clean, high-temp paints eventually burn off, leaving a patchy, unnatural looking manifold.
There is hope however, as an industrial product has found its way into the automotive restoration world. It’s called Slip-Plate, which is a liquid graphite product that is typically used as a dry lubricant in many industrial and manufacturing processes. Slip-Plate uses a liquid solvent binder to which powdered graphite is added. We ordered the aerosol version (which is best for this application) online at www.slipplate.com, but it is available as a brush-on as well. When sprayed, the solvent binder adheres the graphite to the part. After about 20 minutes, the solvents evaporate and the graphite is left on the surface, permanently bonded. The good thing about the liquid binder is that it allows the graphite to flow into the pores of the cast iron, even better than paint, yielding a stronger bond to material. In addition to the better bond, the graphite is designed for extreme temperatures and pressure. This ensures the graphite won’t burn off after just a few trips down the road.
With the technical stuff out of the way, we can get to the point. Spraying the Slip-Plate is much like paint, too much and it will run. Spray the graphite in several thin layers, allowing each coat to dry (between 5 and 10 minutes) before applying another. After the spray dries (20-40 minutes, depending on the atmosphere and thickness of the paint) the top surface will have very dark, dull look. The trick to whole process is to buff the surface using a soft shop towel (don’t use the wife’s good towels, she will probably kill you) which brings the surface to a nice subtle shine. This nearly, perfectly matches new cast iron. It is wise to let the parts sit for 24 hours before running the engine. This ensures the solvents have fully cured and won’t cause any outgassing (release of gasses caused by heating, resulting in bubbles). As a side note, be sure to spray this stuff in a well-ventilated area, it is just like paint and really stinks up the shop.
With everything painted, buffed and the manifolds reinstalled, its time to get down the road. As with all things, there could come a time when the graphite needs a little touch up. Using a small chip brush or even q-tip, any faded areas can be touched up in the car. Spray a little Slip-Plate on the brush or q-tip, dab it on, buff, and you’re done, no need to pull the entire manifold. The graphite blends in very well and, unlike paint, will not show any evidence of a repair.
1. The stock manifolds off this 1969 Buick GS California are not in the worst shape, but that funky orange patina and rust just doesn’t look that good sitting in the engine bay. Something must be done.
2. After a few minutes in the blast cabinet, the manifolds are rust free, but they look a little dull. Cast-iron paint would get the right look, but paint will just burn off.
3. With the manifold resting on a piece of cardboard, the surface was blown off with compressed air to make sure there was no sand or dirt on the surface. A quick wipe with some thinner or paint prep would be a good idea.
4. The Slip Plate comes in 12 oz aerosol cans. At $10 each, the price is right. Each can goes a long way.
5. The manifold was sprayed with a light coat to avoid runs. Slip Plate is pretty thin and it will run fairly easy. If you do get a run, it is not the end of the world, do a little 220 sanding and recoat it.
6. The entire side is sprayed, including the top and bottom edges. The part is left to sit for about 10 minutes to dry.
7. Once dry, the part is flipped over and the backside is sprayed. While you will never see the backside in the car, why only do half the job?
8. This side is left to sit for another 10 minutes. Don’t worry about gasket flanges, it will still seal up nice. If you want, you can tape the flanges off.
9. Flip the manifold back over and spray it again. 2 coats is sufficient.
10. Using a soft shop towel, the manifold is buffed off. It does not take much to bring the shine out.
11. Here is the difference between the buffed graphite and the cured spray. As time goes on, the graphite will loose the shine. Simply rebuff and its back.
12. The entire buffed manifold looks like it just came out of the mold. Not too bad for 30 minutes work.
13. Comparing the 2 manifolds, it is easy to see the difference. The Slip Plate coated manifold looks excellent.
14. The manifold looks right at home now, mounted back up to the motor. We need to wait 24 hours before we run the engine so we don’t have any issues with outgassing solvents. If there is ever any damage to the coating, simply brush a little on and buff off. The Slip Plate blends very well with older applications, so you’ll never see it.
Sources:
Slip Plate
How long will this coating hold up?
This coating is capable of holding up for years. The nice thing about it is that you can touch it up at anytime if you have a scratch or start to notice wear.
What about the creators that are on the manifold as to filling them in to make surface look new again? Is there a filler material I can use that will stick to manifold?
Cast iron manifolds are naturally rough, so this process will retain that look. There really isn’t a good solution for filling manifolds, as the hot and cold cycles tend to make nothing stick long term. JB weld might stick for a while, but I don’t think it would look very good for long.
Great article.
I just got a new cast iron exhaust manifold for my 1953 Citroen Traction Avant. It looks great of course right now, but I’d like it to stay looking good. Painting is an option, but a hassle. This sounds like an excellent alternative.
I assume there must be some kind of chemical or oil left on this new manifold. If I were to rub it down with acetone and a good degreaser, would that be sufficient to then go ahead and apply the
Slip Plate?
Also, if I buff it well, will it still come off on me every time I work under the hood and touch it?
Finally, one last cocern is that the Slip Plate website says it’s good for something like 480 degrees which is way too low. But, maybe that is referring to the “slip” aspect of it.
Thanks,
Dennis
I would definitely degrease the new manifold before painting it with Slip Plate. After a couple heat cycles, the graphite won’t come off very much, but if you are handling the manifolds a lot, then you will likely get some coloring on your hands.
The heat part of the equation is more about function and not the coloring, which is what we are after. The nice part about this process is that you can easily retouch it. Graphite is crystalized carbon, it doesn’t burn up. The binder is more sensitive to heat, but that does not affect the performance in this application.
Thank you very much. I think I’ll give it a try.
Very good to know about graphite for manifold coating. Thanks, Neal
Will it stick to a porcelin coated exhaust manifold?
It really depends on the coating. If you rough it up with a scotchbrite pad, it should.
Had engine rebuilt on my 64 T Bird. the original exhaust manifolds looked awful on the new engine, sand blasted and then applied Slip Plate. Looks great.
Excellent! We’d love to see pics. Share them on our facebook page!
I’m building a 300 straight six for my 67 f100. I’ve slip plated the manifolds adtey are beautiful. I’m considering doing the block and head as well. I’d paint all the tin ford blue. Can anyone think of a reason not to?
*paint wouldn’t stick later if I wanted it to
It is a great way to paint a block, I have done it before. If you want to paint it with regular paint later, then you will have strip the graphite off. But the beauty of the Slip Plate is that it will always look good and can be touched up easily.
Went to the Slip-Plate website and could not identify which product should be purchased for refurbishing exhaust manifolds. Can you list out exactly which one it is? Thank you.
This is the stuff right here. You can buy it at just about any NAPA store as well. https://www.slipplate.com/product/slip-plate-aerosol
What about the internal part of the manifold? Just looking to to help keep the inside corrosion free as much as possible as well, since they are already pulled from the engine.
For inside the manifolds, I like Eastwood internal header coating. It would really well. https://www.eastwood.com/eastwood-hi-temp-internal-exhaust-coating-w-nozzle.html
I’m in Australia and cannot find a Slip Plate distributor here. Other proprietary brands are sold here such as Protech and CRC – these appear to have similar ratios of solvent/graphite powder constituents as the Slip Plate brand. Did you select Slip Plate on the basis of a particular characteristic, or could other brands work just as well?
I have used Slip Plate for many years, it is the best of its kind because they use better quality graphite. The other brands will work too. This particular use is not about the friction-reduction, but rather the look and heat performance, so I would say go for it.
There are a few ways to clean your manifolds- blasting, wire wheel, or chemical stripping. Eastwood and some others make excellent chemical strippers that essentially eat the rust off your metal, leaving you with a fresh surface. A wire wheel will take a lot of time and you will likely never get it fully rust-free. Blasting is the most common method, and can be done with a cheap blaster-in-a-bucket or in a cabinet (the preferred method). Once blasted, you want to coat the manifold immediately to prevent new rust from forming.