Looking For A Coating To Resist Salt Water

Wrong word. You are probably thinking of permeability or penetration. Neither is exactly correct. Salt water molecules can be said to migrate through a permable membrane or leak through a porous coating. Or coatings break down through corrosive or galvanic activity.

In any case, have you even tried looking for conformal coatings or is this your first try at a solution. Like getting us to do your home work. < grin> A google query on "conformal coating" yielded 678,000 hits. ranging from definition of, to applications by, to brand names.

Any reason why you don't encase the pressure sensor in a hermetically sealed enclosure? If its a solid state type pressure sensor, why not use any one of a dozen readily available conformal coatings after wiring it. If re-entry of case is a criteria - as implied by asking about gels - then you must expect this to require service or re-calibration on a periodic basis.

Like so many other questioners on the list, you ask the list members to provide a design solution for you without giving adequate parameters on which to base a recommendation.

what problems do you have with existing coatings available to you? Or are you located in some remote part of the world where conformal coatings are unheard of?

There was a guy several years ago that supposedly synthesized the glue that mussels use to stick themselves too rocks. Supposedly, nothing would stick to it and he was trying to market it as a Hull coating. Any info on that?

Add copper powder to any glue or epoxy and you will have a material that will prevent mussel and algae growth. The oxide of copper, "cuprous oxide" is poisonous to almost all marine life. The Army Corp of Engineers have been spraying copper straight onto structures for that exact reason. Its been working ever since the first copper clad wooden ships.

If all else fails try a condom and a cable tie to hold it on.

I saw a survival show where a person filed a condom with water and made a lens to start a fire.

For starters, I'd look at a methylene bis(4-isocyanatocyclohexane) - hydroxybutadiene polyol resin. Contact Sartomer for a source of hydroxybutadiene polymers. The "rubber" soft-segment portion of the molecule should stand up to salt water for a very long time.

There are many organic coatings as well as hermetic packages that will resist saltwater. If you have done any wreck diving, you will appreciate that there is no long term solution to this problem.

You might try Dow Corning 3145 RTV. It is a MIL grade silicone sealant. I've used this in the past on marine applications (control panel wiring, switches...etc) to seal from salt water (although mostly splash). I don't see it for long-term, but might be worth a shot.

There are a number of polyurethane sealants on the market that might work for you. Some are re-enterable, once I saw an electrical lineman using one based on a castor oil urethane. Check with Caschem - if the company has not changed names.

I don't know if this will work for you. Google this for more info :

ZeroRust is a direct metal phenolic modified alkyd rust and corrosion control a coating, which puts down an impermeable rust proofing barrier at the steel level. ZeroRust has two superior traits (1) it provides maximum adhesion to steel or maximum rust prevention - this is called chemical affinity. (2) Its dielectric ability is extraordinary - steel is isolated from the electrolysis process, which converts steel to rust. (In laymen's terms, this rust prevention starves the oxygen from the substrate, preventing oxidation.) Zero Rust makes an excellent Original Equipment Manufacturer "OEM" coating and is routinely used on new trailers, new structural steel, new oilfield wellheads & manifolds, new mining equipment, new pump & manifold systems, new power generation skids and new tanks. Zero Rust can give your products the rust protection and prevent rust from appearing again.

ZeroRust Performance:
Continued refinement of the ZeroRust formula has netted ASTM-B117 salt spray testing results exceeding 2000 hours at 3.5 mils dry film thickness (d.f.t.). This equates to 600 hours per dry mil, which was previously unheard of in an air-dry system. The Zero-Rust rust protection performance exceeds that of commonly used red oxide, DTM Acrylics, water-borne alkyds and epoxies on these types of surfaces. ZeroRust rust protection performance has been confirmed by industrial, commercial and marine industry. Black and Red Oxide Zero-Rust are recommended as the primers for corrosive services -- including marine, coastal and industrial surfaces. The effectiveness of Zero-Rust on bare steel surfaces is optimized at 2.5 to 3.0 mils d.f.t. over profile. Rule of thumb: Zero-Rust should provide five years of rust protection for every a mil d.f.t. With the addition of a topcoat or a thicker film of Zero-Rust to take the ultraviolet rays, sealing protection can easily double.

Common ZeroRust Applications:

• Offshore Platforms Auto Restorations
• Barges & Ships Refineries & Pipelines
• Port Authority Oil & Gas Processing Equip
• Water Treatment Plants Mining & Smelting Facilities
• Tank & Bridges Vehicles & Trailers
• Geothermal Piping (to 350°) Waste Haulers & Dumpsters
• Fencing & Security Screens Food Processing Plants
• Metal Buildings & Roofing Piping / Structural Steel
• Power Generation Skids Heavy Equipment Recoats
• Dump Trucks

ZeroRust Benefits:
The major difference between Zero-Rust and conventional primers is that conventional primers do not increase their ability to control rust with thicker dry film. For most applications we recommend using 3-4 mils dry film thickness over profile(230-290 square feet per gallon recommended foe 3-4 mils), which is achieved with 2 or 3 spray passes of Zero-Rust across the profile of the surface. For corrosive services, we recommend 5-6 mil DFT using the Black or Red-Oxide formulations applied in 2-4 spray passes.

ZeroRust routinely replaces epoxies, epoxy mastics, alkyd enamels and rust converter maintenance systems. Epoxies and epoxy mastics are used extensively for controlling corrosion perform better than Zero-Rust in underwater or submerged applications. However, Zero Rust performs well in splash zones and remarkably outperforms epoxies in above marine environments. The drawback to epoxies and epoxy mastics are that they need to be mixed correctly, applied within specific time restriction, and cannot be retouched easily. Zero-Rust advantages include no time restrictions during application; no mixing of components, and Zero-Rust may be touched up at any time.

ZeroRust is free of the normal carcinogens found in high performance epoxies and urethanes. Zero-Rust is the perfect rust protection system for the environmentally concerned and those concerned with improving application personnel health safety.

Over Rust: ZeroRust design to be applied over existing rust with minimal preparation. Merely wire brush off any mechanically loose scale or powdery rust. Zero-Rust bites through remaining rust encapsulating it in the phenolic resin system. Scale has air entrapped within its structure and must be removed for maximum protection. Heavy rust scale can be softened for easier removal with the use of Zero-Rust Prep Step. Work the surface as smooth as possible. The smoother the surface and the tighter the remaining rust, the less of product will be needed to cover the pitted surface. With Zero-Rust, no Sandblasting required - Environmental considerations are making sandblasting less viable due to waste disposal and containment.

Partially rusted, partially painted surfaces: When repairing a deteriorated painted surface, total removal of old paint is preferred. When this is not feasible, treat as you would mill scale from the standpoint that the old paint becomes the weak link in the chain. The cleaner and tighter the surface, the better the resultant job. Pay particular attention to paint edges that may lift and curl. For best results, use a rotary sander to feather out exposed steel to adhering paint edges.

Galvanized Steel Surfaces: For aged, rough galvanized steel, ZeroRust will bond with the addition of either 1 tbl spoon of dry Portland cement or half a tablespoon of high calcium hydrated lime per gallon of Zero Rust. Mix thoroughly. For new galvanized steel, use a vinyl wash primer before applying ZeroRust.

Protection at the metal level: Most primers are merely a "fuzzy coat onto which paint will hang. Any protection offered by the top coat is then one-step removed from the steel. Zero-Rust will truly protect, isolate and insulate the steel from rust.

Recoatable: Zero-Rust is a single component system. Scuff sand to re-coat. Most catalyzed systems do not allow re-coating without extensive surface preparation.

Health Safety Benefits of ZeroRust Over Other Mil-Spec Primers: The Zero-Rust rust protection system offers significant health safety benefits over all other high performance primers. Normally high performance in the coating industry indicates urethanes or epoxies which are known "body tissue reactive" materials and therefore cancer causing. The epichlorohydrins and isocyanates all react with water or –OH groups present in all internal & external body tissues. Zero-Rust does not contain any of these components – it is totally non-reactive to body tissues making applications safer, easier and less complicated. Application personnel can feel better about applying these materials knowing of their inherent safety to themselves and others.

ZeroRust MSDS Sheets: