Features May 1, 2002 Issue

Corrosion Inhibitors

The waxy films of CorrosionX MaxWax and CRC HD Corrosion Inhibitor win hands-down for long-term protection. For lighter duty—protecting enclosed electrical and electronic components—we like CorrosionX. WD-40 can still serve as a cheap, short-term shield.

Dozens of spray products found on chandlery and hardware store shelves promise to inhibit rust, fight corrosion and generally protect metals from attack. The labels are confusing at best. All of these products claim to be formulated of secret ingredients that enable them to beat out the competition when it comes to preserving your expensive hardware and electronics. And all claim to burrow under moisture and bond to the target metals. 

For engine mounts, brackets, steering system
supports, and other bilge hardware, use
products that seal with a waxy coat, such as
CRC's Heavy Duty Corrosion Inhibitor.

As it turns out, most of these products, at least those we tested, perform reasonably so long as you take the time to read the small print and select a product appropriate to the job.

What We Tested
The products we selected for our comparison come from four families of protectants—waxy barrier coatings, active fluid thin films, penetrating oils, and PTFE (generic Teflon) dry lubricants. Ultimately we narrowed the group to 17 products based mainly on availability in the major marine discount stores and recommendations from local boaters. While several of the formulations we tested are available in bulk liquids and grease bases, we chose to limit our survey to spray products.

While we tested the products side-by-side outdoors, it's important to understand that intended uses vary widely among the product groups. Just because the label says the product "inhibits corrosion" doesn't mean that it does so in every environment. Nor, for that matter, will it be equally effective on every metal. Waxy barrier coats, for example, are tough and long- lasting, and especially suitable for use in areas that are repeatedly wetted or submerged. However, they can trap existing moisture on the surface of the target metal, allowing corrosion to take place under the barrier coat.

Fluid thin films, on the other hand, work their way under surface moisture, but can be washed away relatively easily; therefore, they do their best work in protected environments—inside a relay box, for instance, or in the engine room.

Corrosion is an electrochemical process. It can occur at the molecular level causing micro-pitting, or on a macro scale, eating away large chunks of metal. At any scale, the corrosion process requires an anode, a cathode, and an electrolyte. Remove any one of the three elements and you inhibit corrosion.

Some corrosion inhibitors, such as the CorrosionX and Corrosion Block, employ passivating agents— chemicals that work at the molecular level to make the target metal less vulnerable to the electrolytic process. The molecules of these passivating agents tend to burrow through existing moisture and corrosion to the target metal's surface, where they spread out like ball bearings on a tabletop. Often many of these ingredients are included in a product, one for each metal the product attempts to protect.

The waxy barrier coats work by preventing the electrolyte (water) from gaining contact with the target metal. Typically the wax components are dissolved in a solvent for delivery. Once the coating contacts the metal it is to protect, the solvent evaporates, leaving the wax behind. (Pure water actually is a poor electrolyte, but marine equipment rarely sees pure water. Water in the boating environment is full of salt and dissolved minerals and is a very efficient conductor of electric charges—a great electrolyte.)

Penetrating oils are thin and flow easily. The more sophisticated penetrating oils are formulated with proprietary passivating agents.

How We Tested
We ordered mild steel test panels from Q-Panel Lab Products, an Ohio company that makes panels in highly controlled processes for coatings industry laboratories. The advantage of using Q-Panels rather than some old hunks of scrap metal is that the Q-panels are guaranteed to be metallurgically identical to each other and free of contamination that could bias our tests.

We cleaned each panel with methyl ethyl ketone (M.E.K.) to remove any residual moisture, and mounted them side-by-side on an 8' long 2x2. Then we treated each plate (except one) with a different product (according to the label instructions) being careful not to contaminate adjacent plates. The plates were labeled alphabetically so our judges couldn't associate a plate with a product (until the end of the test).

We mounted the plate collection—eventually we named it the "rust farm"—outdoors where it would be subjected to the vagaries of a New England winter. To make matters more interesting, we filled a spray bottle with a salt solution and sprayed all the plates once a week. We inspected the plates at 10 and 20 days into the test and finally at 82 days. Grading the results was a simple (though subjective) task—we estimated the percent of surface area that had rusted.

Within a few days, the untreated plate began to scale (rust) as did both of the PTFE-treated plates and two of the penetrating-oil treated plates. (The PTFE products were SailKote and Sea Spray; the penetrating oils that folded early were CRC 6-56 and PB Blaster.)

By Day 20, 3M's 4-Way Lubricant and ProLong SPL100, both penetrating oils, started to permit significant scaling. At the same time, traces of rust began to appear on plates protected by CorrosionX-HD, LanoCote, LPS 3, Corrosion Block, and Lube-It-All.

On the last day of the test, only two panels remained entirely scale free, those protected by CorrosionX MaxWax and CRC HD Corrosion Inhibitor. Both are flexible waxy barrier coatings. Two other waxy barrier coatings—LanoCote and Boeshield T-9 also performed well. As you can see in the table (page 14) the other products all provided some degree of protection.

We added the LPS products to our test relatively late into the program, so final results were not available at this writing, but we suspect that LPS 3, a waxy barrier coat, will end up providing protection similar to that demonstrated by LanoCote and Boeshield.

CorrosionX and Corrosion Block (two popular passivating thin films widely used on electrical and electronic components) fared very well, especially considering that they are formulated for use in relatively protected areas. The 3M product showed early signs of distress but hung in well for the long-term, giving up only 50 percent of its test plate to rust at the end of the test period.

WD-40 and Lube-It-All, both popular with mechanics as all-around penetrants, hung on in the early stages but suffered washout at the end.

Our test confirmed the advice our dads gave us all years ago—when all else fails, read the label. No single product holds the solution for all corrosion protection projects.

Consider first the environment in which you will use the product. The waxy barrier coats perform much better (and longer) in soaked environments than do the thin films. So the waxy coats might be ideal for engine mounts, brackets, steering system supports, and other bilge hardware. None is cosmetically attractive —typically they leave a dry amber/yellow film—so you have to be careful when using them topside.

Of the waxy barrier coats we tested, only LanoCote left a tacky film when dry. The others felt smooth and probably will accumulate less dirt.

Waxes are fine for large electrical components such as battery terminals (after the connection has been made) but aren't so good for switch contacts or PC boards. Waxy coatings must be allowed to dry when applied, and can be removed with a solvent, typically mineral spirits or other degreasers.

All of the wax coats performed well in our tests. If you operate in thermally harsh environments, consider CorrosionX MaxWax. It stays flexible in temperatures well below zero and will resist flow at temperatures up to 398° F.

LPS 3 is especially heavy-duty stuff designed for offshore drilling equipment, outdoor electrical components, underground installations, air brake release springs, and similar applications. It meets several Mil specs.

The active fluid thin films—those products designed specifically for corrosion protection—are widely used on all metal surfaces and electrical components in and around boats. One of our technical correspondents has used CorrosionX and Corrosion Block for years in marine, aviation, and firearms applications, and reports that neither product has ever failed to protect a treated surface when used as recommended. The companies that make these products—Corrosion Technologies and Lear Laboratories—offer their formulations in many varieties including greases and bulk liquids. They're both used by military naval and air services to protect machinery and electronics working in the world's harshest environments.

The penetrating oils all claim to penetrate (thus to free stuck parts), lubricate moving parts, clean surfaces, displace moisture, and protect against rust and corrosion. In terms of protection, all seemed to do OK to the 20-day point, but rapidly lost effectiveness as they were washed off by repeated applications of salt spray and the winter rains. We suspect that if we had reapplied them every 10 to 15 days, they would have done fine. They would also have done well, we think, in enclosed spaces, and they are certainly less expensive than the top-end active thin films from Corrosion Technologies and Lear Labs.

When it comes to "penetrating," WD-40, Lube-It-All, and PB Blaster each have their cheering squads around the yard shops. We didn't find ProLong SPL100 in any of the chandleries, but the auto parts stores say it's a favorite of many mechanics.

LPS 2 is a non-drying oil film and, in composition, seems to have a good blend of properties—penetration, lubrication, and protection. It stays oily and certainly seems to protect well. At 30 days into an accelerated test, it had yet to allow any scaling of its plate. We'll let you know how the LPS products do after the full run.

The PTFE products have unique properties. As an example, SailKote, as its name implies, was originally formulated for application to sails. It reduces wear and friction in sail systems and tends to repel water, salt, and grime. To the extent that it repels water, it acts as an anti-corrosive agent. We included SailKote in our test of corrosion inhibitors only because a number of sailors we know said they use it for that purpose. Our guess is that as a corrosion inhibitor, it's a fine dry lubricant. The same can be said, probably, for Mariner's Choice Dry PFD Sea Spray.

For long-lasting corrosion protection in very wet areas, we can give a thumbs-up to CorrosionX MaxWax and CRC Heavy Duty Corrosion Inhibitor. Both of these products leave a flexible waxy barrier coating on the protected metal surface that stands up to wet conditions.

For lighter-duty work, especially protecting electrical and electronic components in enclosed spaces, we like CorrosionX and Corrosion Block. These fluid thin films contain passivating agents that are safe for use on electronics and precision machined parts. They are especially effective belowdecks where they will not wash off.

For general-purpose rust busting and short-term protection, the old standards turn out to be solid, cost-effective performers. WD-40 and Lube-It-All are especially good.

No matter which protectants you decide to use, it's important to treat all susceptible areas in your boat regularly. Also remember that even relatively small environmental differences can affect the field performance of these products. To make your purchasing choices, read the products' labels to make sure of their intended uses, then refer to our chart.


Also With This Article
Click here to view "Value Guide: Corrosion Inhibitors."

Contacts— 3M Center, St. Paul, MN 55144; 888/364-3577; www.3m.com. Blaster Chemical Co. Inc., 8500 Sweet Valley Dr., Valley View OH 44125; 216/901-5800. Boeshield (PMS Products), 76 Veterans Dr., Holland, MI 49423; 800/962-1732; www.boeshield.com. CorrosionX (Corrosion Technologies), P.O. Box 551625, Dallas, TX 75355; 800/638-7361; www.corrosionx.com. CRC Industries, 885 Louis Dr., Warminster, PA 18974; 800/556-5074; www.crcindustries.com. Lube-It-All (Federal Process Corp), 4620 Richmond Rd., Cleveland, OH 44128; 800/846-7325; www.federalprocess.com. Lanocote Inc., Forespar Products, 22322 Gilberto, Rancho Santa Margarita, CA 92688; 949/858-8820; www.forespar.com. Corrosion Block (Lear Chemical), P.O. Box 1040 Station B, Mississauga, Ontario L4Y 3W3; 800/256-2548; www.learchem.com. LPS Laboratories, P.O. Box 105052, 4647 Hugh Howell Rd., Tucker, GA 30085; 800/241-8334; www.lpslabs.com. Sea Spray (Mariner’s Choice), 6219 Monita St., Long Beach CA 90803; 800/966-9974; www.multchoice.com. SailKote, McGee Industries, 9 Crozerville Rd., Aston, PA 19014; 888/832-6625; www.888teammclube.com. Prolong International, 6 Thomas, Irvine, CA 92618; 949/587-2700; www.prolong.com. WD-40 Company, 3170 Fourth Ave., San Diego, CA, 92103; 619/296–0605; www.wd40.com.

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