Generic types of paint

Detailed description of various types of paint. Production method, areas of use, pretreatment, benefits, limitations etc.

  • Alkyd paints

    Alkyd paints are made from alcohol and acid. They are mostly used for decorative purposes and for protection of steel exposed to relatively mild environments.

    Eiffel Tower

    A tough, high performance protective coating from leading paint manufacturer Jotun has been specified for one of the world’s most iconic structures, the Eiffel Tower. The 120 year old Paris structure is being repainted using approximately 70 tonnes of Jotun’s Mammut polyurethane alkyd-based protective coating as part of an on-going refurbishment scheme.

    Production
    Alkyd paints are made from alcohol and acid with the addition of fatty acid or oil. The addition of fatty acid and/or oil can be varied to give alyds with different properties.

    Areas of use
    Alkyds paints include many different types. They have different properties, but are mostly used for decorative purposes and for protection of steel exposed to relatively mild environments.

    Alkyd paints can only be used above water (not submerged) as the water resistance is poor.
    They are not used on zinc primer or galvanised steel as a chemical reaction - saponification - would occur with the binder, with subsequent blistering and flaking. The drying/curing process is also temperature dependent. This is because alkyd paints dry or cure by absorbing oxygen from the air. This is a chemical reaction and such reactions are always influenced by
    temperature.

    Pre-treatment
    Pre-treatment required can vary from St 2 to Sa 2½, depending on the purpose of the paint and the environment to which the paint is exposed. By modifying the alkyds for example with styrene or silicon, other properties can be achieved.

    Benefits
    • Easy application, both with airless spray, roller and brush
    • Good wetting properties
    • Good adhesion to the surface, and good penetration properties
    • Good weather resistance; Good gloss and colour stability
    • One-pack product: Usually easier to use than two-pack paints
    • Easy to repair details in the paint film during application
    • Good levelling properties
    Limitations
    • Poor resistance to chemicals, especially to alkalis.
    • Limited water resistance: Can usually tolerate ordinary outdoor humidity, but can not be used under water or in especially humid conditions.
    • Limited resistance to solvents: Can swell (lift) under the influence of strong solvents such as xylene, ketones, alcohols and chlorinated hydrocarbons.
    • Can not be used on zinc primers: zinc soaps will be formed (saponification)
    • The film thickness per coat is limited, usually 30-50 microns, up to 80 for special types
    • Must not be overcoated by paints containing strong solvents (will swell the alkyd)
  • Vinyl coatings

    Vinyl coatings are widely used as industrial coatings in chemical plants, refineries and tank farms, bridges and on ships.

    Use
    Vinyl coatings are physically drying. They have been widely used as industrial coatings in chemical plants, refineries and tank farms, bridges and on ships (vinyl tar under the waterline). They are one-component paints, and as such they are easy to apply by airless spray, brush and roller.

    It is, generally, not recommended that vinyl coatings are subject to long time exposure to temperatures exceeding 75-80oC. Decomposition would then take place and lead to yellowing and brittle paint film.

    Many dissimilar paints can be placed under the umbrella "vinyl coatings". The reason for this being that vinyl coatings can be formulated in many different ways. They can be based on various vinyl resins and modified with other binders etc. Therefore, vinyl coatings may differ greatly from one manufacturer to the other.


    Benefits
    • Good chemical resistance
    • Good water resistance
    • Quick drying
    • Not temperature dependent
    • One-component
    Limitations
    • Low solid content
    • Poor resistance against strong solvents
    • Dry heat resistant up to approximately 80oC
    • High content of volatile organic compounds (VOC)
  • Chlorinated rubber coatings

    Chlorinated rubber coatings are widely used as industrial coatings in chemical plants, refineries, tank farms and bridges as well as on ships and other marine structures both above and below the waterline. They are not so sensitive to the ambient temperature during application and drying.

    Areas of use
    Chlorinated rubber (CR) are physically drying paints. They are widely used as industrial coatings in chemical plants, refineries, tank farms, bridges etc. CR has very good resistance to water and has traditionally been used on ships and other marine structures both above and below the waterline.

    Chlorinated rubber coatings are one-component and dry by evaporation of the solvents. They are therefore not so sensitive to the ambient temperature during application and drying.

    They are resoluble which can be considered both as a positive property, but may also be negative: The positive effect will in most cases be the dominating factor as resolubility gives flexible overcoating time, with basically no danger of flaking between coats. The negative side will be that CR-based products are not resistant to most solvents. This implies that strong solvents may destroy the paint film, and in addition there is a danger of solvents being entrapped in the paint film. This happens especially when overcoating a thick CR-system at low temperatures.


    Benefits
    • Physically drying
    • Not temperature dependent
    • Easy to recoat
    • One component
    • Very good water resistance
    • Relatively good chemical resistance
    Limitations
    • Poor solvent resistance
    • Low solids content
    • Relatively poor wetting properties
    • Thermoplastic
    • Dry heat resistant up to approx. 70oC
    • High content of volatile organic compounds (VOC)
    • The chlorinated compounds give off chlorine on ageing
  • Epoxy coatings

    There are a number of different epoxy coatings, each one of them made to meet certain requirements during service.

    Epoxy coatings have some general characteristics. The most important being:

    Benefits

    • Good water resistance
    • Good adhesion to the substrate
    • Good chemical resistance
    • Very good alkali resistance
    • Great resistance to mechanical damage
    • High durability
    • Temperature resistant up to 120oC (somewhat lower/ higher for certain systems)
    • Certain systems officially approved for potable water tanks and in contact with food
    • High solids content/low VOC possible
    Limitations
    • Poor resistance to UV rays: chalks in sunlight
    • Application and curing depends on the temperature (normally above +10oC, cold climate versions down to -5oC)
    • It may be difficult to overcoat cured epoxy
    • They are two-component products and therefore require good mixing and may give increased wastage
    • Moderate resistance to acids
    • Can cause allergy (eczema)
    • Require knowledge to be used correctly
    Epoxy coatings have good chemical resistance, particularly to alkalis. They have good adhesion both to steel and concrete and good water resistance. Epoxy can be modified using phenol, coal tar and hydrocarbon resin to give special properties, e.g. better chemical resistance, better penetration, better water resistance etc. One drawback with many epoxy coatings is that they contain large quantities of solvent. However, types have now been developed with high solids content (mastic products) with excellent "all round" properties. There are also a solvent-free epoxy coatings which are used for drinking water tanks. Water-borne epoxy coatings are increasingly being used today because they give a better working environment. Chemical resistance, however, is slightly reduced.

    Application 
    Before painting, the two components must be mixed in the correct ratio. The curing process is a chemical reaction between the base and curing agent, so application and curing are temperature dependent. It is important to apply the paint before the chemical reaction has proceeded too long after mixing. When the pot life (usage time) has elapsed, the paint becomes dry and hard and impossible to apply.

    Areas of use 
    Different types of epoxies have different areas of use:
    • Epoxy mastics. Very versatile coatings: Industry, ships and offshore. Under and above water (Topcoat required when exposed to UV-light). On most substrates due to good penetration and adhesion properties.
    • Pure epoxy. Chemical tanks, potable water tanks and as an all-round coating system on ships and industrial plants. Require blast cleaning to minimum Sa 2½.
    • Phenolic epoxy. Chemical tanks. Even better properties than pure epoxy. Require blast cleaning to minimum Sa 2½.
    • Coal tar epoxy. Ships. Under water, particularly water ballast tanks.
    • Solvent free epoxy. Drinking water tanks and where environmental restrictions are decisive.
    • Water-borne epoxy. Industry where conditions can be controlled (humidity and temperature)

  • Epoxy mastic coatings

    Mastics are among the most versatile coatings for industrial and marine use. Due to their very good resistance to water they are used on ships and other marine structures both above and below the waterline.

    Epoxy mastics consist of epoxy resin modified with a hydrocarbon resin (certain variations should be expected for different manufacturers) and a curing agent. The hydrocarbon resin is used to enhance the moisture resistance, flexibility and the wetting properties of epoxy coatings. They also make the paint more user friendly and economical in use.

    Areas of use
    Mastics are among the most versatile coatings for industrial and marine use: Industrial coatings in chemical plants, refineries, tank farms, bridges. Due to their very good resistance to water they are used on ships and other marine structures both above and below the waterline. One should bear in mind that being an epoxy they will chalk when exposed to sunlight. For decorative purpose a topcoat can be applied.

    Epoxy mastics are in many respects similar to coal tar epoxy (CTE). However they are much more versatile coatings and nearly all drawbacks with CTE are reduced or eliminated.

    Benefits

    • Surface tolerant
    • Light colours
    • Very good water resistance
    • Very good wetting properties
    • Good chemical resistance
    • High solid content
    • High build (thick coats)
    • Cold climate curing agent
    • Dry heat resistant up to 90oC

    Limitations
    • Chalking
    • Temperature dependent
    • Not to be applied on thick coats of physically drying paints
    • Minimum DFT 150 microns by airless spray

  • Polyurethane coatings

    Polyurethanes are mainly used as topcoats in an epoxy paint systems. They fill a vital niche for high-performance applications over metal, concrete, wood and plastic.

    Polyurethane coatings can be both one- component (moisture cured) or two-component. Here we will deal with two-component paints only. Two-component polyurethanes are among the most versatile coating types. They fill a vital niche for high-performance applications over metal, concrete, wood and plastic. Polyurethanes are mainly used as topcoats in an epoxy paint systems.

    These coatings show excellent colour and gloss retention for outdoor exposures. In addition, they are resistant to chemicals and solvents. Polyurethanes are chemically curing paints and as such the curing process will depend on the temperature. The lower temperature limit is normally 0oC.

    An alternative to the Isocyanate cured polyurethane coatings is the epoxy acrylic or acrylic - acrylic type. Such curing acrylics have the same characteristics as the polyurethanes. The pot life is much longer, the drying time very short, but the curing time is somewhat longer.

    Benefits

    • Very good weather resistance
    • Excellent gloss durability
    • Very good chemical resistance
    • Very good solvent resistance
    • Cures down to 0oC
    Limitations
    • Two-component
    • May cause skin irritation

  • Polyester coatings

    Polyester coatings are quick curing, glass flake reinforced, high build coatings. They provide very long term corrosion protection. The resistance to water and moisture is excellent and the use of polyester coatings for salt and fresh water exposure is widespread.

    It has exceptionally high abrasion resistance making them ideally suited for application on decks and walkways, hulls of icebreakers, tidal and splash zones of steel structures and concrete.
    They offer very good adhesion to both steel, blast cleaned to Sa 2½, and concrete

    Polyesters are usually two-component coatings applied at normal temperature. The polyester coating have a rather short pot-life and should therefore be applied by a two-component airless spray equipment (Regular airless spray is possible, and in fact, often used). At 20oC the pot life is approximately 40-45 minutes. Styrene free polyester, where the styrene is replaced with vinyltoluene, can be applied down to 5oC when applied with two-component airless spray equipment.

    The polyester coatings are dry to handle in 2 hours (at 23oC) and can be applied in a film thickness of 300-1500 microns per coat.

    Benefits

    • Quick curing
    • Variable curing time
    • Application with airless spray
    • Excellent mechanical strength
    • Glass-flakes reduce shrinkage, increase mechanical strength and water resistance.
    • Very good chemical resistance
    Limitations
    • Temperature dependent
    • Short pot life
    • Recoating interval 2-12 hours
    • Bad curing may be experienced on zinc primers and galvanised surfaces.

  • Vinyl ester coatings

    Vinyl ester resin based coatings are known for their good solvent and chemical resistance.

    They offer very good adhesion to both blast cleaned steel and concrete. Both concrete and steel surfaces should be grit blasted.
    The vinyl ester is often called a "problem solver" especially for inside tank protection. The vinyl ester is effective against a wide range of chemicals. The temperature resistance is also higher than for most traditional paints.

    Vinyl esters are often referred to as linings. The world "lining" in the coating industry is commonly defined as a material used to protect the inside surface of a tank, vessel, or similar structures from highly corrosive or potentially highly corrosive environments.

    Vinyl esters are normally two-component coatings applied at normal temperature. They are usually applied in thick coats (2 x 750 microns). The vinyl ester coatings have rather short pot life and should therefore be applied with two-component airless spray equipment.


    Benefits

    • Very fast curing
    • Very good adhesion
    • Very good abrasion resistance
    • Very good chemical resistance
    • Very good solvent resistance
    • Can be applied with normal airless spray
    • Glassflakes improve abrasion resistance
    Limitations
    • Short pot life (approximately 45 minutes)
    • Overcoating interval: min. 2 hours, max. 24 hours
    • Limited shelf-life
    • Approximately 6 months at 23oC
    • Dependent on temperature during application
    • Only to be applied on blast cleaned steel (Sa 2½)

  • Inorganic zinc coatings

    Inorganic zinc coatings are very resistant to different chemicals and especially solvents. Used as primers they have the ability of providing cathodic protection. This will contribute to protecting the steel substrate and reducing the risk of having undercutting corrosion.

    The main reason for applying a zinc containing coating is to have a primer with the ability of providing cathodic protection. This will contribute to protecting the steel substrate and reducing the risk of having undercutting corrosion. For the cathodic protection process to work properly, it is extremely important that the coating contains a sufficient quantity of zinc metal, usually above 75% weight of the dry film for water-borne and 82% for solvent borne paints.
    They are very resistant to different chemicals and especially solvents. Zinc ethylsilicate (solvent-based) and alkali silicate (water-borne) are also often used inside storage tanks for solvents because of the extremely good solvent resistance. Inorganic zinc coatings have, generally, not been used for services implying continuous water immersion.

    Typical practice in the use of inorganic zinc coating systems varies with the exposure environment and type of structure. One coat of inorganic zinc, typically 75-125 microns DFT, is often used for tank lining. The water-borne zinc silicate has to be applied with conventional spray. The solvent borne zinc-ethylsilicate, however, is excellent to apply with airless spray. Careful monitoring of the relative humidity is important during application and curing. Multiple topcoats over inorganic zinc coatings are used for offshore structures, ships, industrial plants, refineries, tanks, bridges etc.


    Benefits

    • Very good solvent resistance
    • Very high heath resistance (max 400oC)
    • Very high mechanical strength
    • Very good adhesion to blast cleaned steel
    • Relatively good re-coatability
    Limitations
    • Requires humidity for curing
    • 2-pack
    • Max. DFT: 100 microns
    • At higher DFT tendency of mud-cracking or checking

  • Organic zinc coatings

    Zinc epoxy is often used as a holding primer both at industrial plants (during maintenance) and within shipping. It is quick drying and the overcoating interval is relatively short. It also enables cathodic protection.

    The main reason for applying a zinc containing coating is to have a primer with the ability of providing cathodic protection. This will contribute to protecting the steel substrate and reducing the risk of having undercutting corrosion. For the cathodic protection process to work properly, it is extremely important that the coating contains a sufficient quantity of zinc metal in its formulation, usually above 75% weight of the dry film for waterborne and 82% for solvent borne paints.
    The zinc epoxy shall be applied on steel blast cleaned to the standard Sa 2½ (ISO 8501-1). They offer very good airless spray application properties, are quickly recoatable, and show excellent compatibility with most coatings (except alkyd: saponification). It is a good primer for multicoat systems, both for new constructions as well as for field maintenance applications.

    Zinc epoxy is often used as a holding primer both at industrial plants (during maintenance) and within shipping. It is quick drying and the overcoating interval is relatively short. It has very good adhesion, good impact resistance and is heat resistant up to approx. 120oC. The abrasion resistance is good.
    The disadvantages of zinc epoxy compared with inorganic zinc is first of all that the galvanic protection of the steel is limited as the electrical conductivity of the binder is low. Secondly, the acceptance level of chlorides on the substrate is lower. This is particularly a drawback for marine exposures.


    Benefits

    • Good corrosion protection
    • Good adhesion
    • Good mechanical strength
    • May be overcoated with all types of paint, except alkyds
    • Chemically curing
    • Short overcoating time
    Limitations
    • Temperature dependent (5oC)
    • Two-component
    • DFT: 25-90 microns (25-30 microns for underwater use)
    • Dry heat resistant up to 120oC
    • Not acid and alkaline resistant (resistant at pH range 5-9)