Friday, 22 May 2015

Corrosion (Rust) Paint Damage


[: Rust is a general term for a series of iron oxides. The term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Rust consists of hydrated iron oxides Fe2O3·nH2O and iron oxide-hydroxide (Fe O (OH), Fe (OH) 3). Given sufficient time, oxygen, and water, any iron mass will eventually convert entirely to rust and disintegrate] 

Iron (or steel) rusting is an example of corrosion, which is an electrochemical process Rust is the common name for a very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen, so readily in fact, that pure iron is only rarely found in nature. For iron to become iron oxide (FeO), three things are required: the iron itself, moisture and oxygen.

Road Salt

One of the surest signs of winter in cold-weather regions of the United States is the build-up of salt in tire treads and on roads (and on your boots, and in your house…). The concept of salt-lining roads is easily explained: when you add salt to water, its freezing point dips below the normal 32 degrees Fahrenheit, so the outdoor temperature has to dip even lower than that for ice to form on the roads.

Although dry salt is inert 15 – 20.oF (9 – 29.oC) is considered the lower limit for salt to melt snow and ice but once H2O, even in the form of moist air (i.e. humidity) is added the freezing point is lowered and the sprayed brine solution (pH 8.5) used on roads will have an adverse effect (the formation of rust and/or corrosion) on the vehicles paint and undercarriage. 

Magnesium Chloride (MgCl2) attracts moisture from the air making it more aggressive than salt because it is active even when “dry”. Magnesium Chloride is basically ‘liquid rust’. It clings to everything and it attracts moisture – and it does not wash off easily”.

When washing the vehicle ensure that all salt removed to avoid a brine solution remaining on the paint finish. Using a durable protection (Collinite Insulator Wax) will provide a sacrificial and renewable protection to the vehicles paint finish.

Nearly all highway de-icers on the market are made from one, or a blend of, five materials — calcium chloride (CaCl2) sodium chloride (NaCl) potassium chloride, magnesium chloride (MgCl2) and urea. 

What makes these products different is how quickly they work and at what temperatures. This is determined by whether the deicer releases or absorbs heat upon contact with snow and ice.
Magnesium Chloride and Calcium Chloride are used as deicing agents these materials are especially destructive because of their ability to cling to the under body of a vehicle and re-crystallize as they slowly dry out.By nature they attract and absorb moisture from the surrounding environment, keeping them in a semi-solution state for extended periods of time, which multiplies their corrosiveness

Exothermic de-icers, which release heat to melt the ice, work the quickest and are effective at a broader range of temperatures. For example, solid calcium chloride releases heat and is effective down to –25.oF. Endothermic deicers, which absorb the sun’s heat and use it to break ice down to liquid brine, work more slowly and are effective at a smaller range of temperatures For example, solid sodium chloride absorbs heat and is effective down to about 20.oF. The predominant chemical in a blended product will determine its performance.

The salts (salt CI and water H2O produce oxides, which cause corrosion) used for freezing point depression in a sprayed brine solution (often mixed with grit / sand for tyre adhesion) commonly used are;

Brake dust or rail dust is very small, almost microscopic particles of steel, iron or their alloys. These particles carry a positive charge (due to friction) while the vehicles they land on are carrying a negative charge. The vehicle surface becomes a magnet, attracting and bonding the ferrous metal particles to the vehicle’s paint surfaces.

The corrosive chemical compounds generated then proceed to etch (corrode) the clear coat, the metallic particles (brake dust) penetrate and act as a conduit spreading the corrosives through the paint film system (and the sheet metal), which results in erosion of the paint surface, that shows on the surface as tiny rust spots (rust blooms)

Environmental damage to paint comes in a varied range of threats; acid rain, road salt, tree sap, hydrazine an extremely active acid that is found in jet fuel, industrial fallout, ultra violet radiation (UV) and other airborne contaminants are very detrimental to a vehicles paint film surface. They are all forms of environmental contamination and given the right catalyst; reactivity (heat) plus moisture, they will become acidic. During this process the metal absorbs oxygen from the water and forms iron oxide (rust).  

Given the porosity of paint they permeate the paint matrix down to body metal.
Although present on all paint surfaces, sintered brake / rail dust is most noticeable on light coloured paint surfaces, especially white. These contaminants are invisible to the naked eye, once they start to oxidise, and turn orange; this is when the problem will be brought to your attention, even on brand new vehicles.

Stages of Corrosive Paint Damage

Stage One- Iron particulates causing surface staining leading to substrate corrosion
Stage Two - Contaminants have permeated the paint matrix causing discoloration and corrosion damage
Stage Three - Particulates and corrosive compounds causing severe damage to the paints resin (binder) system

Signs of Paint Surface Contamination

         Dark coloured specks
         Brown or Orange (rust) coloured stains or specks
         Yellow stains
         Small metal coloured flecks
         Rough texture
         ‘Water spots’ or marks
         Surface etching
         Paint ‘stains

Acidic Contaminants Identification

Ferrous Metal - 
·        Light colored vehicles: Small rust orange dots with black in center of stain.
·        Dark colored vehicles: Small white or silver dots with a "rainbow hue" around the particle. The surface will also feel rough to the touch.

Industrial Fallout
·        The surface feels rough to the touch and may exhibit crystalline deposits.
·        Usually ferrous metal is present, as well as water spots.

Acid Rain
·        Surface will exhibit irregular discoloured spotting.
·        Dark colored vehicles will show cloudy or grey spots where the acids have started to etch the paint.

Rust Removal / Treatment
Careful sand blasting is the best method for removing medium to heavy rust but you need to be careful not to warp the sheet metal. The metal can be sanded to remove surface rust but if it's pitted you'll need to use a metal conditioner/rust converter to stabilize the surface before priming.
Phosphoric acid may be used as a rust converter; by direct application to rusted iron, steel tools, or surfaces. The phosphoric acid converts reddish-brown iron oxide (rust) to black ferric phosphate (FePO4)

"Rust converter" is sometimes a greenish liquid suitable for dipping (in the same sort of acid bath as is used for pickling metal), but it is more often formulated as a gel, commonly called naval jelly. It is sometimes sold under other names, such as "rust remover" or "rust killer". As a thick gel, it may be applied to sloping, vertical, or even overhead surfaces.

After treatment, the black ferric-phosphate coating can be washed off, leaving a fresh paint surface. Multiple applications of phosphoric acid may be required to remove all rust. The black phosphate coating can also be left in place, where it will provide moderate further corrosion resistance
Follow up with a rust protection aerosol can of ValuGard Rust Inhibitor and/or some Eastwood Heavy Duty Anti-Rust. If you use a product like Picklex 20 to stabilize the rust you want to make sure you work it into the surface with a scuff pad then wipe it off after a minute or two.

Coat with an acid free, direct to metal primer like epoxy primer that doesn’t’ contain any acids. If you plan on leaving the metal without primer for any length of time the Picklex 20 will protect it from flash rusting as long as it doesn't get wet.

Neutralizing -
Washing the paint film surface with a slightly alkaline car wash concentrate and thoroughly rinsing will neutralize the contaminants and remove them from the paints surface Detailer's clay removes embedded brake dust and other contaminants by encapsulation, thereby eliminating the primary cause

By applying a suitable cleaner and then a rust inhibitor (POR-15® Products) it will arrest corrosion on contact without leaving a sticky residue that would attract dirt, dust or grime. Corrosion attacks metal by an electrochemical (galvanic) reaction with water as the catalyst. It penetrates the corrosion cells, emulsifying the moisture and separating it from the metal, leaving an ultra-thin barrier to protect from further damage.

Since most corrosion begins in crevices, (seams), it is important to have the capability to penetrate these crevices in order to form a protective barrier. Many heavier or more viscous products don't penetrate crevices, instead they form a `bridge', and while this may isolate the crevice from further contact with the electrolyte it does nothing to eliminate the presence of existing moisture or surface corrosion. Injection into a seam or crevice with an aerosol or spray eliminates this problem Por-15® 

Products Marine Clean
After the paint surface has been subjected to a chemical cleaning its protective layer (s) have been removed and the paint surface left without protection, so it is very important that a wax or polymer protection be applied immediately.

Rust Inhibitor Treatment
A three-part rust inhibitor treatment by POR-15®
1. Marne Clean ™ cleans and degreases in one application without leaving residues, noxious fumes or flammable solvents. Its water not solvent-based and it cleans without leaving residues, no other cleaner works as fast or as well. It makes petroleum-based cleaners almost obsolete because it can be diluted 5:1with distilled water, thoroughly rinse with clean water after completing your cleaning job.

2. POR-15™ Metal Ready provides the best adhesion for POR-15® on any metal surface, including aluminium and shiny polished metal surfaces.

3. POR-15® is a high-tech, high performance rust-preventive coating designed for application directly on rusted or seasoned metal surfaces. It dries to an incredible rock-hard, non-porous finish that won't chip, crack, or peel, and it prevents rust from recurring by protecting metal from further exposure to moisture.

Rust Prevention

A British company Bilt-Hamber Laboratories has a new product - Dynax UC new high-performance anti-corrosion wax provides a touch-dry firm wax film that's virtually invisible, a low film thickness see-through protective shield. Its firm wax like film is rich in unique metal seeking corrosion inhibitors that stop existing and prevent new corrosion.  It can be applied to bare metal or painted surfaces in fact anywhere where a discrete and powerful inhibitor is needed. 

This product is aimed at those that want a see-through tack-free film that adds a lot of corrosion protection but preserves the factory look of the underside or lower panels, it’s removable too, so after winter it can be stripped if required, or left in situ and topped up every couple of years, or more if you wish; very easy to use.

Completely safe to use on the vast majority of paint coatings and is ideal where dark colored waxes or under seal would detract from the painted finish of vehicle bodywork or underside.

The touch dry tough wax film also provides mechanical protection to the protected surface too.  The ideal product to provide high levels of protection during the winter months; to apply -clean any loose dirt, rust flakes or other debris and then clean with a power-washer, allow product to dry and then apply thin even coating

I would like to think that these articles become an asset to anyone who is new to detailing and to professionals alike, as well as industry experts who seek to advance their knowledge.
I hope the above article was informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire.

I would appreciate it if you would share this article as it helps other detailers further their knowledge.
Questions and/ or constructive comments are always appreciated.

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