Research on Rust

Rust is the killer in old cars. Repairs are expensive. The problem starts off hidden. It is insidious and can be dangerous. There were two rust problems on my 912 that were obvious when I bought the car, The front body pan had rust damage between and around the front suspension attach points (now fixed, see below) and the passenger door sill had a visible damaged area. I am so paranoid about rust that I almost never wash the car with a hose and try not to drive it in the rain.

Cavity Waxes

The current issue (October(?), 2000) Classic Sports Cars magazine has an article on cavity waxes. These materials do not seem to be discussed much in the U.S, but are designed to be placed in hard to reach areas such as fender wells and door bottoms to prevent rust from forming. Any pre-existing rust should be first converted from ferrous oxide with an acid wash. Their recommended product brand is Dinitrol, an English product that may not be available here. The magazine considers the materials required for old daily driver cars.

A couple of links mentioning cavity wax:
  • A Primer on rust.
  • Article on the application of Teroson cavity wax.

Front Body Pan

652-849-4.jpgI knew that the front body pan had rust damage when I bought the car. I first planned to have it fixed the winter following purchase, but judging by the ominous suspension noises and fresh cracks around the damaged area I moved the time table forward. If left alone, this particular problem can be dangerous because the body pan provides the attach points to the front of the torsion bars. Imagine turning a sharp corner and having the torsion bar go straight!

This problem was professionally repaired in early September, 2000. Here is the story.

Passenger Door Sill

652-849-24.jpgPassenger side rust damage in the door sill. This extends to the rocker panel. It was caused by an accumulation of dirt and gravel in the front of the rear wheel well, trapping moisture next to the metal whenever the roads get wet. Check your car by shining a flashlight into the wheel well. Wash out any dirt found. I cleaned and used naval jelly in the rusted area. The purpose is to slow down the rust until it can be properly repaired. Otherwise it could spread very quickly - and it may in spite of this effort because it is impossible to get to all affected surfaces. Then I sprayed the area with Rust-Oleum 'Rusty Metal Primer' and 3M Undercoat.

Rust Research

Steps to stop continuing damage to rusted areas:
  1. Remove old rust by wire brush, rotary grinding or brush.
  2. Change remaining iron oxide into iron phosphate using Naval Jelly.
  3. Neutralize the phosphoric acid with baking soda paste.
  4. Clean up with water. Dry with clean rags and heat gun. The bare metal will oxidize quickly so next step must be done promptly.
  5. Paint with Rust-Oleum Rusty Metal Primer.
  6. After primer has dried, spray with 3M Underseal Rubberized Undercoating Nr. 08883. Black.

    Gas Tank Rust

    My tank had enough rust in it to clog fuel filters. I called the POR-15 people and asked who I should take my gas tank to to get treated with their material. They recommended Vintage Auto in Oroville (now moved to Williams). I had it fixed at the same time as the front body pan restoration. It cost about $80.

    Here is an article off the WEB on using POR-15 for fixing gas tank leaks.

    Subject: Fuel Tank repair - POR-15 report
    From: ??michael <juriga@IDT.NET>
    Date: Tue, 3 Nov 1998 14:31:43 -0500

    Hey all,

    Update on my rescued Interceptor. I just finished prepping the tank. I DID NOT use crappy Kream. Read on.

    The Interceptor I've rescued had sat outside with 1/3 a tank of gas for about a year and a half. The internals were definitely rusty though still tight w/o leaks. I needed to do something about the internals but didn't want to use Kream (because it is not a permanent fix and the problems it can cause when it decides to go are *NOT* fun.) My work with restoring my 1970 Chevelle SS had brought me in touch with a company called Restomotive who produce a product called POR-15. This stuff is amazing. All the resto rags rave and car related Internet sites are a-buzz about it. When used properly, it stops rust *DEAD*. It forms a super hard surface that is very hard to scratch or chip. Even my Evil Twin Joey (the ToeCutter) Thorne, who works on boats, knew about POR-15 and had favorable things to say about it. If a rust repair product can work properly in a Marine/Saltwater environment than it has GOT to be good. Awhile ago, I found a tank prep product kit in their catalog. I have been very happy with other products of theirs, so I have been waiting for an opportunity to try this one. Hey, they even show a V65 Sabre's tank in the catalog. I think that this is a sign.

    The kit contains: Marine=Clean (a water based, alkaline cleaner/degreaser, supposedly environmentally friendly but I wouldn't let it sit on your skin for very long), Metal Ready (a mildly acidic solution which completely turns rust into a neutral Zinc Phosphate. Much nicer to work with than the highly acidic hydrochloric solution in the Kream kit. Also, Metal Ready can be saved and reused.), Tank Sealer (which reminds me of POR-15 Silver), a piece of cloth and a disposable brush (to repair pin holes and leaking seams, which I did not need to use, so I cannot vouch for.) A heavy duty version of the kit also has a step that will completely remove a previous tank lining like Kream.

    Use of the kit is not as quick as using Kream. YOU MUST TAKE YOUR TIME! If you follow the directions given to you by POR-15 and the suggestions I've outlined here you should be okay.

    Cleaning the tank

    Seal all openings and vent tubes on the tank. Duct tape is suggested, but it kept coming off of the two large openings on my tank due to LOTs of water. I improvised by slipping the gas cap into a surgical glove and installing it the way it would normally go to seal the top hole. luckily had a large cork the size of the fuel gauge sending unit hole to seal that as well. Using the Marine=Clean, mix one part cleaner and one part boiling water. Pour into tank and then seal it tight. I agitated the solution in the tank by gently rocking it back and forth. Rock and roll. Rock and roll. Make sure the cleaner gets everywhere. The cleaner needs to be in the tank for at least 24 hours, more for heavily varnished or dirty interiors. I would agitate for about 20 minutes, and then let it sit for an hour or two. Then I'd agitate some more and let it sit again, but in a different position than before. After 24+ hours I dumped the cleaner out and flushed liberally with water. I used my bathtub as I don't have good access to an open area w/ a hose. Your wives or SO may kill you for this as it's messy, but not damaging. Flush it well. You want to remove as much alkaline solution as possible for the next step, which is more acidic.

    Rust destruction/ "etching"

    When I say etching I don't mean like the extremely harsh Kream method. Metal Ready is technically acidic, but pretty mild in comparison to the Kream Kit's (Phosphoric or Hydrochloric Acid?) Metal Ready's main job is to CONVERT rust to a neutral Zinc Phosphate. Any etching properties are pretty minor. Metal Ready takes about 30 minutes to work for a tank in the condition of mine. Heavy rust will take longer. Again I'd agitate the tank/solution in a slow rocking motion. Turning and rocking and rolling and turning. Watch a movie that you know by heart when you do this. I watched Mad Max again. When the tank is done, remember that you can reuse Metal Ready, so I siphoned it out of the tank. Again, flush liberally with water. You should see black flakes of particulate now instead of rust colored. That is the zinc phosphate converted rust.


    Okay, you're pretty excited now that the rust is gone. The job is going well and you want to keep the momentum going. Before you go pouring the sealant into the tank STOP! The tank **MUST** be absolutely bone dry. POR-15 cures with water. If a single drop of water (or sweat) drops into your pint can of POR-15 while you are working THE WHOLE FREAKING CAN IS WASTED! This tank sealant is the same.

    After the flushing out from the Metal Ready step I again siphoned out as much of the water still trapped in the tank as I possible could. Letting the tank sit in the sun won't dry it. Letting it sit for 10 weeks won't dry it. You need to introduce warm moving air to dry the internals. I removed all the tape and stuff sealing the various holes on the tank. I set the tank up with a hair dryer set on low w/ heat blowing into the main hole. I left it blowing warm air into the tank for around 4 hours. The next day I let it blow warm air in half hour intervals about 3 or 4 times. Then, when I was ready to seal the tank, I let it blow cool air for an additional 2 hours. I may have overdone the air thing, but I wanted to take no chances. I wanted this done right.

    Sealing the tank

    After the hair dryer this step seems anti-climatic. I resealed the openings, this time merely with duct tape. I poured the contents of the sealant can into the tank. It is the consistency of paint with a heavy fumes. DO NOT GET THIS STUFF ON ANYTHING ELSE. If you do wipe it off IMMEDIATELY. It won't come off once dry. I'm serious. Wear gloves, because you'll be wearing a for weeks if you don't. Ordinary paint thinners do not work with it. It can be thinned with the POR-15 specific thinner (not available in this kit as there is no need for it.) Agitate the tank again in slow motions allowing time for the POR-15 to coat the interior. I took about 45 minutes to be sure. On my tank there was no easy way to get the excess POR-15 out due to a collar around the interior of the main filling hole. I used a turkey baster to remove the excess. I also blew compressed air into any small diameter tubes/holes to be sure that I don't develop a restriction or clog due to a cured POR-15 blockage. I set the tank aside to dry/cure. A well ventilated area is a must for this. I installed an exhaust fan in my bathroom window and let the tank sit in there for the night while the most fumes were present. I also let the tank sit upside down so that any excess POR-15 that I couldn't remove would puddle in the air pocket that is always present, even in a full tank of gas so my fuel capacity wouldn't be effected. If you have leaks at the seams of your tank, you might want to consider letting the POR-15 cure so that it puddles into these areas, sealing them forever. The tank is fully cured and ready for gas after 4 days. Mine is completed now with a ROCKING coating ready to go.

    So that is how it went. It is a time consuming process. It is not *DOWN AND DIRTY* quick and easy. but guaranteed, if you do it right you'll never have to do it again. While not being difficult it is also not "simple". You do need to take your time and be careful, especially to fully dry the tank with warm moving air. You *CANNOT* be in a rush. Leave about a week of off and on work to complete the task. But the results are worth it. If this coating/finish is anything like the other POR-15 products I've used that nothing short of an A-Bomb will effect it. This is the only permanent fix I know of short of buying a new tank. At the price of $29.95 and a week's worth of time I'd say it is worth it.

Naval Jelly

A pink phosphoric acid based gel for safe and easy removal of rust from iron and steel. Naval Jelly is useful for preparing metal surfaces for painting. Paint will adhere better to iron and steel surfaces when cleaned will Naval Jelly. It is also an ideal pre-treatment for all galvanized surfaces prior to painting.

For general cleaning of iron and steel, apply full strength with a paint brush, roller or sponge. Allow a dwell time of 5 to 20 minutes depending on the amount of rust to be removed. If heavy encrustations are present, use a wire brush to clean before applying. In severe conditions, it may be necessary to apply Naval Jelly several times. If this occurs, allow a longer dwell time, overnight if possible.

The product is 100% soluble in water. Can be neutralized with a baking soda paste.

There are two main reasons for using phosphoric acid for rust removal: It dissolves rust at a much faster rate than it dissolves iron, and it leaves a nice iron phosphate coating on the clean metal surface. The reactions are: (a "_" before a number means to subscript the number.)

(1) Fe_2O_3 + 2 H_3PO_4 -----> 2 FePO_4 + 3 H_2O fast

(2) Fe + H_3PO_4 -----> FePO_4 + H_2 (gas) slow

In reaction 1, the rust (Fe2O3) gets turned into iron phosphate and water; this mostly gets washed away when you rinse the part. The phosphate part of phosphoric acid is responsible for this reaction. Reaction 2 is the reason you may see some bubbles. The iron itself is actually dissolving, but this is a relatively slow reaction. The H+ ions from the phosphoric acid are responsible for this reaction. You're not going to lose any worthwhile amount of metal to this reaction, but this is also the reason you don't leave the acid on the part for more than about 15 minutes. The layer of FePO4 that is left on the surface adheres strongly enough due to surface effects that it does not wash away with the rinse, hence the good protection from further rusting. (Note: reaction 1 is a simple exchange, 2 is oxidation-reduction; i.e. Fe+++ ---> Fe+++ and Fe(0) --> Fe+++.)

3M Underseal Rubberized Undercoating

From the can, "Sprays easily, dries quickly, and provides a very tough film that is resistant to abrasion. Remains flexible, Ideal for coating repair areas, such as wheel wells, trunk areas, undercarriages, and floor pans".
  1. Remove all rust scale, oil and grease from surfaces to be coated. Surface must be clean and dry.
  2. Apply to bare or primed metal.
  3. Shake well.
  4. Hold can 10 to 12 inches from surface and apply a uniform coat. Allow product to dry 3-5 minutes, then apply 2nd coat.
  5. After use clear nozzle by inverting can and spraying until free of material.
  6. Air dry a minimum of one hour before applying additional paint. Use of a flex agent is recommended if painted with enamel or lacquer.


The active ingredient is phosphoric acid.

Ospho is greenish liquid with the consistency of water. Brush or spray it on rust after just knocking off the loose scales and it pretty much stops rust dead. It also leaves no residue. There is a product called "Neutra-rust". It may have ospho as the active ingredient but its in a milk-like base that changes from beige to blue/green when applied. It then leaves a sand-able coating.

See Hillman Marine. (No idea if these guys are relation to me).

Ospho stops rust, prepares rusted surfaces for painting. Ospho is a primer-not a paint. You do not have to remove tight rust. Merely remove loose paint and rust scale, dirt, oil, grease and other accumulation with a wire brush. Apply a coat of Ospho-let it dry overnight, then apply the paint. When applied to rusted surfaces, Ospho causes iron oxide to chemically change to iron phosphate - an inert, hard substance that turns the metal black. One gallon covers 600 square feet.

part#    description
1280-011 ospho 1-qt
1280-01  ospho 1-gal

Snee Rust Dissolve. For removing rust and scale; for best results, remove dirt, old grease and oil and heavy soil foil from metal surfaces. Rinse thoroughly with clean clean water and apply rust treatment. Allow to react for 5 to 15 minutes to dissolve all metal oxides. for heavy rust and corrosion, wire brush surfaces to remove scale. Allow surfaces to air dry completely. Apply primer paint.

part#    description
1280-05  rust dissolve 1-gal
1280-055 rust dissolve 5-gal

Wonder II Clean away excess dirt, oil and grease. Remove loose rust, scale and flakes with a wire brush. Apply Wonder II. To form a protective coating, allow to dry completely without rinsing (5-10) hours. For heavy rust repeat application.

part#    description
1280-06  wonder II
Last modified: Fri, 03 Nov 2000


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