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 5oC.
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 30oC.
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.
