The selection of a coating system is very complex and even though this catalog do not pretend to became you an expert in the matter, it is convenient to present a terminology and to consider the basis.

A.- General Outlines.- Easy to apply and maintain coating, must be superior to a paint in adherence, chemical resistance and hardness and must be resistant to moisture, atmosphere and water exposure.

It is impossible to formulate a coating containing all characteristics that is why it is important to emphasize the best functions a coating must have, even then put aside functions of less importance.  In order to compensate weak points, a coating system consists in several coats of painting, primers and finishes, each one develops a specific function, and each characteristic are complemented among themselves.

B.- Primer.- The primer is the base of a painting system and have big importance in a well -planned program of maintenance.
To develop its commitment, the primer must be formulated to adhere itself on the surface that is going to protect and resist the service conditions.
The importance of the primers justifies a brief explanation of different types of manufacturing primers applied in different construction materials.

1.- Primers for Steel and Iron- This primers must formulated to give a good adherence and prevent corrosion underneath the film, through the combination of inhibitor pigments of corrosion and a vehicle, at the moment of drying form an stable film in a reasonable time of period. The most frequently used inhibitor pigments are, minium, zinc oxide, dust zinc, basic chromate of lead and zinc chromate.

The type of used Vehicles are:

a.- Linseed oil, characterized for its slow drying, adherence and great humectants properties.

It has a disadvantage, that it deteriorates easily because of moisture or contact with derived oil products.

b.- Synthetic Resins.- Are extremely versatile because its fast drying, resistance to chemical attack and impermeability to water.

c.- A combination of both previous points gather a slow drying and the penetration of the linseed oil with the hardness and chemical resistance of the synthetic resins.

d.- Synthetic resins, specially processed to give a slower drying than primers type (b) and a high fluid grade and penetration.

The fabricated primers of synthetic resins based are found more acceptable in the industry now a day; although it’s fast drying requires a good surface preparation, giving best results when it is applied above metal cleaned with sandblast.  In areas where for security or operation reasons or economic issues are not possible to sandblast, it’s preferably use primers of linseed oil or a combination of synthetic resins with linseed oil.

2.- Primers for Galvanized Iron.- The galvanic process leave a thin oil coat on the metallic surface, that must be eliminated by any method of the section 11.

The galvanized steel has physics and chemical properties different of steel that is why in many occasions the conventional primers have no adherence.

3.- Primers for concrete.- The just finish concrete surfaces contain great quantities of humid and alkaline salts that destroy the coatings that in some other circumstances will work satisfactory.  For this reason, it is necessary to let age the concrete before make any paint application or neutralizer with an acid muriatic solution dilute as soon as the moisture have been dissipated.   The primer must be formulated to give a good adherence above concrete.

4.- Primers for bituminous surfaces.- The bitumen and asphalts are soluble in the solvents and oils commonly used in painting, they have tendency to bleed even in spite of apply several coats. To rectify this situation, it is necessary to seal the bitumen surface with a primer-sealant of emulsion water type.

5.- Primers for wood.- The primers for wood, especially when it’s going to be exposed to weathering, must be formulated to give at the moment of drying a uniform film and no absorbent, very sealant and elastic enough to resist dimensional changes due to temperature and humidity variations.

C.- Coatings.- The anticorrosive primers do not have by itself the resistance qualities and appearance that the industry demands. It is necessary to coating with other materials that can give them one or more of the following advantages:  Protection, duration, color, high temperature resistance, resistance to chemical agents or weathering, etc.

D.- Coating Selection.

l.- General Outlines.- While the paintings date from more than 6,000 years, the protector coatings as known nowadays, are relatively new and come to life as a result of the industrial revolution, at the beginning of the XX century. Before that date, the painting was used mostly with decorative purposes, but the development of the modern chemical, petro-chemical and marine industries requires of coatings not only for decorative purposes, but to be used as engineer materials to prevent the iron corrosion and the concrete. The claim created by the industry of best materials has accelerated the research and nowadays there are hundreds of industrial coatings formulated to satisfy a specific function..
All coatings have a common characteristic.

a.- They are applied as liquids to be later converted in a solid film. Some of these coatings are baked, other catalyzed, some others dry fast, other ones in a slow way, and some others never get totally hard.

b.- All coatings have 2 basic ingredients:

Vehicle and pigment. The vehicle contains an agglutinant that besides of been capable to form a film, must have the ability to accumulate small pigment particles. The vehicle is in liquid form and its change to solid can come into effect in several ways; in case of few coatings as shellac, the vehicle go dissolved in volatile solvents that by evaporation turn it to solid.    In case of the conventional painting of oil, there is a reaction with the air oxygen that changes the resin to solid state.

2.- Type of Coatings.- The protector coatings are classified according with the type of resins or vehicle with which they have been formulated, being more commonly used in corrosion control, alkyds, epoxies, phenolics, chlorinate rubber, vinyl and inorganic vehicles.

Each one of these generic types has specific properties that are interest to point out:

a.- Alkyd Enamels.- Are synthetic materials that are used in major proportion and have replaced in large part the conventional oil paintings, in the works of industrial maintenance, calculating that a 51% of the industrial maintenance is done with this type of paints.

b.- Baked phenolics.- the baked phonolic coatings, almost without exception, show an excellent resistance to water, acids and strong solvents, and they are characterized for its little resistance to alkaline mediums.

The cost of these materials is generally very low, but its application cost is high due that they need a magnificent surface preparation, multiple coats, and a pretty high baked temperature.

c.- Epoxy Coatings.- The coatings of epoxy resin based are fabricated in three general types: Modified with oil, catalyzer and baked at high temperature.

Epoxy esters.- The modified variety with oil, which it is known as epoxy esters, have intermediate properties between the conventional alkyd enamels of high quality and the plastic coatings.
The epoxy esters are formulated to give an alkali resistance bigger than the alkyd enamels, but because of its oil content it is not recommended for immersion or continues contact with strong alkalis.     In general it is good in resistance to acids, as long as it gives to the film an adequate thickness, but for this type of service, definitely they are inferior to vinyl coatings or chlorate rubber.

Dries fast and under certain circumstances it is possible to apply up to two coats the same day. They have good moisture resistance and they can be recommendable to continue exposition at temperatures up to 150C. In outdoors they chalky very fast still when this phenomena seems to be only a change in the surface that don’t affect the integrity of the film.
   
These characteristics have reduced its application area to interior surfaces exposed only to the action of weak chemical vapors.

Catalyzer Epoxies.-  Are two components coatings that need to be added a curing agent before its application. They are formulated in three varieties that differ themselves only in the catalyze type or the used of curing agent. The cured epoxies with polyamides has a lightly inferior chemical resistance but more resistance to water and weathering and more easy to adhere at each type of surface still when they are not conveniently prepare.

The cured epoxies with adductive aminics are prepared previously react to a portion of catalizer with epoxy resin. These materials are less sensitive to climatic conditions
and in general they have major resistance than cured materials as animas and polyamides. The catalyze epoxies have a great solvent resistance even when the most important characteristics it’s remarkable resistance to alkaline materials. Its resistance to acid is good with the exception of the concentrated organic acids or oxidant acids. They are very hard and resistant to abrasion and are recommended for applications up to 180 C.
The catalyze epoxies are much more permeable to water vapor than chlorate rubber coatings or vinyl, but this disadvantage can be defeated formulating them to give a major film thickness.   

All epoxies have a very marked tendency to chalky and to change color when it is exposed to inclemency and sunlight, characteristics that have limited its use as maintenance materials in industrial plants.  Since epoxies polymerized in a form of very hard materials of high molecular weight, after a certain period of time the surface gets a glazing appearance that offer too many problems for coating.

It is necessary to treat the surface with a hard solvent or by cleaning with sandblast gust so the surface lose smoothness and give a good anchoring for subsequent coats.

Baking epoxies.- The baking epoxies have a major chemical and solvent resistance than any other epoxy, but require a high temperature bake to get a complete polymerization. Its use is limited to coating tank interiors to store concentrated caustics or solvents.

d.- Vinyl Coatings.- the vinyl coatings are formulated chlorate copolymer based and polyvinyl acetate and are the more versatile materials ever known with an excellent water resistance, still in continuous immersion, excellent resistance to all along pH scale, great duration in exteriors and insuperable in brightness and color retention.  

The film have an excellent acid and alkalis resistance but tend to fall out when it is in continuous immersion in contact with alkalis materials.
For severely applications, it is recommended to apply them in minimum thickness of 5mils of inches.
The vinyl coatings are thermoplastic, which allow an easy coating. Its main disadvantage is the very limited resistance, for solvents and from heat, very charged sensibility to contamination between coat to coat. The film is more resistant to tension than adhesion and is apply on contaminated surfaces, tend to fall out very easily.

e.- Coatings of chlorate Rubber.- Coatings of chlorate rubber are formulated of resin based fabricated by chlorination of natural rubber. With very good acid and alkalis resistance, dry fast and have a great duration to weathering still when they have some tendency to chalky.

With the purpose to reduce its price, very often the alkyd resins are modified, which it allows to formulated with a much bigger content of solids, they are easier to apply and coating and less sensible to contamination between coat to coat, still when its chemical resistance, specially alkalis, reduces considerably.

f.- Epoxy Coatings – Coal Tar.- The coal tar is one of the most ancient material that is known and definitely one of the most effective barriers in the water transmission. However it does not have enough resistance to alkalis, neither the temperature nor the abrasion. Blending it with an epoxy resin, develop one of the most versatile and resistant materials for the oil and petro-chemistry industry.

A catalyzer reacts joining coal tar molecules and epoxies, turning out an extremely resistant material that collects the good characteristics and properties of both components. 

It’s a cheap material and easy to apply, for which it has an extensive use for interior coating of storage tanks of crudes and  gas station, buried pipes,  bottoms and sides of barges and scows, etc.

Its black color is a disadvantage, the fact of loosing brightness and get chalky very fast in weathering and  it is very difficult to maintain, as time goes by the film cure and became harden at the point of when apply a new coat it will be necessary to treat the surface previously.

g.- Inorganic Coatings  of Zinc.- The coatings of inorganic type are unique in regards with its ability to support severe expositions to weathering and continuous immersion in strong solvents.  In relation to its duration to weathering, still unspecified, but there are applications that after 20 years they are in perfect conditions. Its resistance to all common solvents, including chlorinates, is excellent, for which it is recommended to coat gas storage, airplane-gas, alcohols, acetone, esters, etc.  It has mechanic properties that make them similar to a galvanized for hot immersion and in general they are magnificent primers to coat with resistant coatings to chemical corrosion.

The main disadvantage of the inorganic silicate of Zinc is its chemical limited resistance and the critical conditions of applications, because the recoat has big zinc content, it is not recommendable for acids and alkaline environments and its application requires a magnificent surface preparation and a careful control of the film thickness.