MARINE COATINGS

Marine Coatings

           

            The application of shipboard marine coatings consumes a significant portion of Chief Mate’s time and the company money. Many Mates have very little training in this area prior to being assigned the task. There are runs Such as the North Atlantic where coating will be difficult or impossible. The reduction in crew size means that the correction of improper coating will not be easy and even proper application will require budgeting of time with a minimum waste. It is vital that marine personnel, afloat and ashore, understand the subject of marine coatings. A poorly coated ship is a waste of time, money, personnel and may be subject to more frequent breakdowns due to rusted equipment.

A. Methods of surface preparation

            If the pretreatment of steel is insufficient, it is not possible to expect satisfactory results in the paint application. The main surface preparation methods are Blast Cleaning, Power Tool Cleaning, Hand Tool Cleaning and Chemical Cleaning.

B. Primary surface Preparation

         

1.      Mill scales, rust and other foreign matters are to be removed to the grade of near white by blast cleaning.

2.      After the blast cleaning, all blast abrasives and dust on the steel surface must be completely removed

C. Shop primer

           

Rust will return to the surface within a short time so it is necessary to apply a shop primer immediately.

D. Secondary surface preparation

            Secondary surface preparation should be performed before painting because the surface of steel plates that have been coated with shop primer will be damaged by fusion cutting, welding, distortion and exposure to corrosive atmospheres.

E. Storage stability

            When paints are stored outdoors, they will deteriorate in a shorter period. It is therefore recommended to store paints indoors in a cool place.

F. Painting with an airless sprayer

            When paint is being applied by an airless sprayer, it is necessary to select suitable painting equipment. The following table provides a guide in the selection of airless sprayers.

Guide Table for the selection of Airless Paint Sprayers

Pressure Ratio                         23:1                             30:1                             45:1    

Max. Pressure of                     160kgf/cm²                       210 kgf/cm²                      300 kgf/cm²

nozzle

Max. Pressure of                     7 kgf/cm²                           7 kgf/cm²                           6.6 kgf/cm²

Air supply

Max. Discharge                       1.9ltr/min                     11.4ltr/min                   12.6ltr/min

Quality

Application                             General finish              Chlorinated rubber      Epoxy resin paint,

                                                coating, anti –                         paint, epoxy resin        tar epoxy paint,

                                                corrosive paint, etc.     paint, etc.                    high viscosity

                                                                                                                        type paint, etc.

G. Atmosphere which is not suitable to paint

1.      When the atmospheric temperature is less than 5^oC.

2.      When there is high humidity.

3.      When there is a possibility of bubbling because the surface is schorched by the sun.

4.      When there is a possibility that moisture, sand, dust, or other foreign matter will adhere to the paint while it is still wet.

H. Ventilation

                       

            It is required that the space being painted is properly ventilated to avoid the possible risk of ignition of paint or gasoline fumes and explosion.

1.      Blast Cleaning:

By the use of blast cleaning, mill scales, rust and harmful substances can be completely removed.

There are four grades of abrasive sandblasting:

           

White Metal – the surface of metal steel can be completely seen, all paint is remove. This is the most commonly been used.

           

Near White Metal – the surface of the metal steel cannot be completely seen but having a spots and tiny particles of paint is still remaining.

           

Commercial Blast – a blast which only portion of paint is removed from the metal surface.

                       

Brush off Blast – a blast which uses only the normal pressure to remove the dust, dirt, stain. Sometimes paint is affected to be remove partially.

      Weld splatter is a black residue which spread out and left when the metal is heated from welding. It is removed by sand blasting, with the use of power tool or hand tool.

      Wet abrasive blasting is a blast of air and water. It is accomplished by a very high pressure of air and water.

      Sandblasting leave a rough surface so that the applied paint will easily stick or bond to the rough surface of metal.

      Metal is required to be degreased before sandblasting to have an good and efficient finish of sand blasting.

      Pickling is a process of removing and cleaning the dirt or dust particles from the pipe lines with the use of chemical or acid substances.

2.    Hand and Power Tool Cleaning:

      Hand tool cleaning, handling is very simple and easy unlike power tool cleaning, handling is relatively little effort but rust removing and cleaning can be efficient in performance.

Hand and power tools aboard the vessel:

            Scraper – it is use to remove large or small scales of dirt, paint etc.

            Chipping hammer – it is use by striking large formation of rust manually.

           

Pneumatic power brush – it is mostly use for removing small formation of rust, the rust left by the use of jet chisel and before applying of paint.

           

Pneumatic disc sander – it is use for removing rust and sometimes for cutting.

           

Pneumatic hammer – use for removing large and deep formation of rust which cannot be remove by jet chisel.

           

            Jet chisel – use for grinding and removing bulks of rust.

Wire brush – it is use to remove formation of rust manually in narrow corners which cannot reach by power tools.

           

      The source of energy we use is compressed air supply with 5 to 10kgf/cm² and man power in using this tool because we carry flammable cargo.

Rust – a brownish corrosive coating formed on iron exposed to moisture; a chemical change of iron and oxygen.

            Mill scale – it is a pulverize rust which forms in the metal surface.

           

            Scale – it is a large fragment of rust which forms from the metal surface.

           

            Pitting – a grave mark formed in the metal surface made by scale of rust.

            Corrosion – destroy of metal gradually by chemical action.

           

      Feathering the edges is done to put back the original form of edge by removing the formation of rust.

      When operating any cleaning equipment, safety equipments should be worn like safety goggles, ear muffs, leather or cotton gloves, safety helmet, safety shoes and boiler suit.

3. How are the following metals prepared for coating:

                  Aluminum – in engine room it is coated mostly with a heat resistant paint.

                 

                  Galvanized Steel – it is painted only with epoxy ester primer coat.

                  Copper – is not to be painted unless otherwise specified.

                 

                  Lead – is not to be painted unless otherwise specified.

                 

            Electrolysis is a process of MGPS (Marine Growth Preventing System) which produces chlorine to avoid the (accumulation, production) of marine life. It is commonly occurred in the engine room pipes suction from the sea chest.

4. Shipyard Hull and Boot Topping Coatings:

           

            The purpose of hull coating is to prevent corrosion by preventing the metal to be exposed and color, to have beauty and distinction.

            We have “Jotun” brand of paint for bottom painting which is “Tin free Self-polishing AF Tar-epoxy type”. For boot topping has a different type of coating which is “epoxy type”, first the shop primer then anti-corrosive, next is undercoat and then finish.

        

            The hull and boot topping was applied first with shop-primer by airless spray. Before the primer was applied, the surface was cleaned from dust and dirt and must be dry.

           

            When humidity level is rising, it brings the surface moisture and makes application difficult. They keep observing outdoor conditions and maintaining tank temperatures. Ventilations were kept continuously operated during painting process.

            The bottom area flat part was coated with a total dry film thickness of 475µ, bottom area vertical part with a total of D.F.T 525µ and topside with a total of D.F.T 180µ. The drying time of coat depends on the type and thick of paint and the outdoor temperature. Normally the gap of drying time before applying of coat is 8 – 12 hours in a atmospheric temperature of 30^oC.

            The hull must be cured or must be completely dry and ready before flooding.

            The draft marks, load line, plimsol mark and deck line which is permanently slope-out marked on our vessel. It is painted with finish “Jotun Pilot II – white oleoresinous type.

5. Cargo and Ballast Coating:

            In ballast tanks we used “Tar-epoxy type” of paint, in cargo tanks and cargo piping, we used epoxy type system of paint.

            Surface preparation was applied by sandblasting and vacuum of all blast abrasives and dust on the steel surface before the application of paint will commence.

           

            We do not have any long lasting paint such us “Demitcoat” onboard.

            There were anodes installed inside the ballast tank which is not needed to be painted.

6. Application of Marine Coatings:

            For the protection of any surface, an adequate dry film thickness is required. The thickness is recommended by the paint manufacturer for each coating system used. The thickness will be specified in mills or microns. The calculation of the theoretical coverage or spreading of the coating is determined by the volumes. The volume solid is defined as the percentage of solids expressed in volume in paint. One gallon of paint at 100% volume solids will cover 1064sq.mt at 1micron thickness. The paint label or schedule may give the percent of volume solids in the paint. It will also tell the theoretical coverage at the recommended thickness.

Three factors that will make the actual coverage vary from the theoretical are:

   Wastage – there will be wastage if paint is not properly applied into its specific surface, dropping of paint while applying

        

         Porosity – this will occur if paint is applied into its specific surface, if paint is not properly mixed well or mixing ratio is not been followed which will cause metal to be exposed and rust will form.

        

   Surface roughness – the surface will be rough when the surface is not properly cleaned or the surface is exposed from dirt or dust after the application. It may also the surface becomes rough if it was exposed from wet like rain or any other form of water after the application.

7. Definition of Terms

        

         Pigment –concentration of color on a particular of paint.

         Thinner – it is use for mixing up with paint to make thin viscosity.

         Mixing ratio – it is the amount of specified mixing content of paint with another substance.

         Gloss – it is mixed with paint to have a shine on a smooth surface.

        

         Semi-gloss – same with gloss but less shine.

        

         Matt – not shinny (in surface).

         Enamel – it is a type of paint which is a glass-like substance for coating metal or pottery. It dries hard and leaves a glossy finish.

   Non-slip aggregate – is a mass or body formed of particles or parts that retain their individuality.

        

         Heat resistant – paint which cannot be destroy by high temperature of heat. It is mostly applied in engine room machineries and pipes which is always exposed from heat.

        

         Chalking – this occur when the paint is not properly mixed before application.

        

         Epoxy based – a type of paint which is mostly used in application of metals.

        

         Polyester based – a synthetic type of paint resin.

         Thermoplastic – it is a substance which becoming soft when heated and hardening when cooled.

         Lacquer – a hard glossy varnish.

         Varnish – a type of paint which is mostly applied on wood for finishing.

        

         Shellac – resinous substance used in varnish.

8. Applicators

            There are several types of applicators for marine coatings. Each type is designed to perform a certain task in a superior fashion. While many of the applicators are to an extent interchangeable, it will find that each has its special use depending on the coating and surface.

Brushes:              

         2” flat brush – use for cutting in or in small areas when using any coating.

         4” flat or chip brush – used for wide application in small areas.

                 

         Stencil – it is use to guide in printing fonts from the surface.

                 

Bristles:

         China – it is use for letterings and bordering application

        

   Nylon/polyester – it is use for metal surface but must not be used for line shellac or varnish work as it tends to leave streaks.

Paint Rollers:

         Lamb’s wool – use for ceiling, roofs, inner and outer walls and used with Wall and Ceiling paints on a water or oil base. It gives a textured finish according to the surface and type of paint.

         Polyester – use for any kind of metals. It is mostly used onboard. It also gives a textured finish according to the surface and type of paint.

Spray guns:

         Airless – use for spraying paint without air.

           

         Air – use for cleaning the surface from dust and drying.

         Gun Cups – use as the handle and controls to spray or shut.

            The roller and brush is measured by length in centimeter. Roller and brush is cleaned depend on the paint been used and there is a appropriate type of thinner for cleaning each type of paint except for water base type of paint. After cleaning, soak the used brush or roller in water to avoid drying which makes the bristles hard.

9. Safety while painting

Select the right paint specification or process

                 

            Care must be taken to ensure that the correct painting process is adopted. For example, it would be fatal to apply a slow drying oil base and heavily pigmented primer with the intention of finishing with a modern synthetic product, surface tension would quickly encourage film cracks and peeling. Therefore, always keep to the same system following carefully the manufacturer’s recommendation.

Stir the paint well before use

            Even today, with all the advantages of science and technology, a large number of paint failures are occasioned by not stirring the paint before use. Good pigment dispersion prevents heavy deposits sinking and lying on the bottom of the can or drum, but the medium and pigment will, to some extent, settle out without severe sinkage. This encourages users to apply the paint without careful stirring. Technical failures experienced by not allowing adequate stirring are inconsistent gloss for enamels, poor coverage performance or early film failure.

Give the surface the right pre-treatment to repainting

            Prior to re-painting, all old loose paint should be scraped off. Rust dots, if any, should be removed with a steel brush. Rust-scrapping must be done to the point where the paint has good adhesion to the iron. Make sure that no rust has penetrated down under the old paint. Also make sure that there are no cracks in the old paint. Should there be any, they must be scrapped and brushed down to the iron. Undamaged areas of the old paint need not to be removed, but the old film should be washed with a common soda solution, and then rinsed according to the directions in surface preparation.

Adapt the priming to the finish required

            Always bear in mind that the glossier the surface, the more important it is to ensure the proper preparation of that surface; for the least unevenness will be magnified on a high gloss surface.

Ships bottom (underwater area)

            After the careful removal of marine life from the heel by scraping and rinsing, be sure to remove all mill scale and rust pitted areas. It may be necessary to chip and scrape all corroded parts to get a clean painting surface. Be sure to let the surface dry thoroughly before any coating is applied.

        

            In spots where rust is exposed during the preparation, it is important to “coat in” these areas with an anti corrosive composition, followed by the application of one or more coats of anti fouling to a grade suitable for the ships service life.

The belt (boot topping)

            Special attention must be paid to this vital area of the vessel, which is normally contaminated with oil and grease from continuous harbor pollution. It is most important to clean this area off, using a suitable cleaning agent or detergent. The preparation as suggested in the foregoing paragraph should be followed through.

Topside and superstructure

            When dealing with the maintenance of the Topside and Superstructure, it is most essential to remove salt water deposits and to comply very carefully to the instructions as laid down in the points illustrated in our General Painting Instructions for the Guidance of Ship’s Crew.

Decks

            After carefully preparing steel decks and following the principles laid down in the General Painting Instructions, it is important to apply a good rust preventive primer prior to the application of the Deck Paint.

Main engines and machinery

            Where re-painting is to be considered, special attention must be paid to adequately cleaning the surface and making it free from oil and grease deposits before re-coating is attempted.