MARINE PAINTS

General Information

Paint Technology

•Paint Types

•

Comparison of Paint Types

•

Safety

•

Safety Equipment During Painting

•

Maintenance

•

Treatment before Painting

•

Application

PAINT TYPES

Paint consists of binder and pigments.  In its liquid form the binder is usually

diluted by a solvent to render the paint fit for application.

The combination of binder and solvent is called the vehicle.

Due to the fact that the binder determines the film formation and the general

performance of the paint coating, paint will be divided into two main groups

according to their solidification or film formation which may be either a physical or a

chemical process.

Physical Film Formation

- HEMPATEX / HEMPAFLEX.

This mechanism can be described as evaporation drying.  The solidification solely

relies on evaporation of the solvent which is a physical process.  The binder in the

dry film is chemically the same as it was in the can.

The principal binders are of widely different nature ranging from

the “Traditional”: Asphalt, Bitumen, Tar

to

the “Advanced”: Chlorinated Rubber, Vinyl and Acrylic.

A special physically drying mechanism is used in emulsion paints.  Although the

main diluent is water, the dry film cannot be redissolved in water.

Physically drying paints have the following characteristics:

Require good ventilation during the film formation in order to evaporate the

solvent.

Sensitive to solvents, including their own solvent (except emulsion paints).

Thermoplastic (they become soft at high temperatures).

Chemical Film Formation

- HEMPALIN / HEMPADUR / HEMPATHANE.

The chemical processes differ which accounts for the division into subgroups.

1.

Oxidative drying

The drying mechanism is due to the fact that the binder contains drying oil.

When exposed to air the binder takes up oxygen and is thus converted into a

chemically new material.  The most widely used type of oxidative drying

binder is

alkyd.

Epoxy ester

belongs to this group too.

2.

Chemical curing

In chemically curing paints the film is formed by chemical reactions in the

binder.  By definition the reactions do not include oxygen uptake.  Normally

the paint is delivered in two parts to be mixed prior to use.  The best known

types are epoxy and urethane (isocyanate).  Some isocyanates are delivered in

one-pack systems.  For these systems the curing mechanism is a chemical

reaction between the isocyanate binder and the water in the air.

3.

Inorganic zincsilitate

This group includes both one-pack and two-pack products.  some types are

waterborne and some solvent-borne.

In waterborne zinc silicate the film is formed by a chemical reaction between

zinc and silicate and a reaction between silicate and carbon dioxide.

In solvent-borne zinc silicate the film is formed by a chemical reaction

between zinc silicate and water.

Generally, chemical cured/dried paints have the following main

characteristics:

Temperature dependable (for temperatures below 10°C the film formation will

be impossible or very slow).

High solvent resistance (own solvent included).

Composite

In order to improve some characteristics the paint manufacturers have succeeded to

develop composite paint containing binders from the two main groups described

above.  Modified alkyds as

methanelakyd,  styrene alkyd,  epoxy ester

and

silicone

alkyd

belong to this group.

Styrene alkyd has shorter drying time and better wearing qualities than normal

alkyd.  To obtain this better performance you must pay a higher price for the paint

and improve the quality of the pre treatment.

NB:

Urethane alkyd and epoxy ester are synergistically alkyds and have

characteristics  different from polyurethane and epoxy.

Another composite paint is coal tar epoxy produced by selected tar products.

Coal tar epoxy has better water resistance than pure epoxy due to the tar content,

but poorer solvent resistance resulting in  redissolving and bleeding through new

paint film during recoating.

A very popular composite paint is

vinyl tar 

which during the latest years has

increased its application.

The popularity of vinyl tar compared with coal tar epoxy is caused by temperature

insensibility (the solvent evaporates for temperatures below 10°C) and simple

recoating of old paint without preliminary roughening of the surface.

Finally,

epoxy-mastic

products were introduced at the end of the eighties.  These

products are modified epoxy products with a good surface tolerance.  this means

that contrary to normal pure epoxy products, these products can be applied on

power tooled surfaces, which means that epoxy-mastic products are very suitable in

onboard maintenance.

COMPARISON OF PAINT TYPES

WORK-ABILITY

SAFETY

The below-mentioned measures are based on the instruction named

“Teknisk forskrift A nr. 1-6 af 26. august 1996”

issued by

The Danish Maritime Authority.

Labelling of cans etc.

Paint distributed in Denmark is normally supplied with a code number indicating the

degree and sort of unhealthy content.  The evaluation is based on eight hours

exposure.  The code number is a two number code, the meaning of which is

described below.

A----------------B

Volatile part I I

I

Remaining part I

Code A is a measure of the health risk by inhalation of vapour deriving from the

volatile part of the paint including organic solvents.  Code A can get the values

00-0-1-2-3-4-5 where OO involves minor sagety arrangements and 5 involves serious

ones.

Code B is a measure of the health risk of the remaining part.

1. When skin and eyes are in direct contact with the product.

2. By inhalation of drops or dust deriving from the product.

3. By consuming the product.

Code B can get the values 0-1-2-3-4-5-6 where 0 involves minor safety arrangements

and 6 involves serious ones.

In addition to the labelling described above, all paint distributed in EEC countries

are labelled with content declarations, safety- and risk sentences.

SAFETY EQUIPMENT DURING PAINTING

1. Pre-treatment

Disc sanding/

High pressure

Grit washing

wire brushing

hosing

Safety

Filter mask

Safety goggles

Safety goggles

Equipment

Safety goggles

Waterproof suit

Waterproof suit,

gloves

2. Painting outdoor, Epoxy Mastic

Code No. 3-5

M E T H O D

Brush or roller

Airless

Safety

Equipment

Gas mask, gloves, shield,

Air supplied full mask,

hood, protection suit

gloves, hood, protection

suit

3

. Painting indoor, Epoxy Mastic

Code No. 3-5

M E T H O D

Brush or roller

Airless

Small surfaces

Safety

Equipment

Gas mask, gloves, shield,

Air supplied full mask,

hood, protection suit

gloves, hood, protection

suit

Large surfaces

Air supplied full mask,

Air supplied full mask,

gloves, hood, protection

gloves, hood, protection

suit

suit

Description of Safety Equipment

Dust masks

Shall contain a fine dust filter class II b.  The filter protects both against dust

particles and poisonous particles in the dust (e.g. during grinding in old red lead

paint).

Safety Goggles

Close fitting glasses.

Gas masks

Shall contain a filter protecting against organic vapours.

Filter alternatives: Normal filter (class II) or large filter (class III).

Air supplied full mask

The air must be clean and produced by a compressor unit, dedicated for respiration

use only.

MAINTENANCE

Requirement and Planning

The protective coating system must be systematically maintained like engines and

mechanical equipment.

Weather exposing, mechanical damages and spill of chemicals will influence the

condition of the protective paint film and slowly destroy the film.

Preventive maintenance will reduce the extent of corrosion and postpone

replacement of steel.

Preventive maintenance will involve periodic inspection of all painted surfaces and

an estimation of the need for paint treatment.

Below a plan is listed for examination and the most common types of detachment.

Examination

Divide the surface into small areas.

Examine each small area according to the checklist below.

Is the area corroded?

Is the corrosion local (edges, welding seams) or scattered?

Are rust stains observed?  and where?

Is the paint peeling off, locally or scattered?

Is the paint blistered?

What has caused the corrosion?

-  Mechanical detachment or local wear?

-  Sharp edges, rough welding seam or condensation?

-  Insufficient pre-treatment due to bad design?

-  Paint system worn-down?

When the examination is finished, type and extent of maintenance can be

decided:

1.  Improvement of the construction.

2.  Touching up.

3.  Touching up followed by full coats.

4.  Cleaning of large areas followed by recoating on ship, at yard or in

harbour.

Reg. 1

If corrosion is caused by sharp edges, wrong design, uneven welding seams

or welding spatter, it might be attractive before painting to improve the

condition of the steel by rounding sharp edges, smoothing welding seams,

removing welding spatter and, if possible, making drainage.  These

improvements will extend the lifetime of the paint system.

Reg. 2

If the paint system in general is in good condition with only local corrosion

such as mechanical damages or spot corrosion on edges or welding seams,

then touching up is sufficient.  Full coating must never be carried out for

cosmetic reasons only.  An intact paint film will protect the surface even if

the film is bleached of the sun.

Reg. 3

If the surface is slocally corroded and the paint film is disintegrated on large

areas, it might be suitable after touching up to apply one or more coast on

the entire surface.  Before painting, all areas to be cleaned thoroughly

according to special instructions.

Reg. 4

Regardless of running maintenance, the condition of the paint system might

be so poor that recoating aflost is impossible with a sufficiently good result.

In such cases, recoating must be carried out with professional equipment

(grit blasting, airless application) in harbour or during dry docking.

Demand on pre-treatment and painting

To obtain a sufficiently good quality of the painting, the surface must be

thoroughly cleaning and all grease, oil and loose rust scales removed before

painting.

In addition, the thickness of the paint film must not be below the specified

film thickness in order that the resistance against corrosion and mechanical

damages can be sufficient.

Pre treatment and painting will be described in a future section.

Reg. 1

If corrosion is caused by sharp edges, wrong design, uneven welding seams

or welding spatter, it might be attractive before painting to improve the

condition of the steel by rounding sharp edges, smoothing welding seams,

removing welding spatter and, if possible, making drainage.  These

improvements will extend the lifetime of the paint system.

Reg. 2

If the paint system in general is in good condition with only local corrosion

such as mechanical damages or spot corrosion on edges or welding seams,

then touching up is sufficient.  Full coating must never be carried out for

cosmetic reasons only.  An intact paint film will protect the surface even if

the film is bleached of the sun.

Reg. 3

If the surface is slocally corroded and the paint film is disintegrated on large

areas, it might be suitable after touching up to apply one or more coast on

the entire surface.  Before painting, all areas to be cleaned thoroughly

according to special instructions.

Reg. 4

Regardless of running maintenance, the condition of the paint system might

be so poor that recoating aflost is impossible with a sufficiently good result.

In such cases, recoating must be carried out with professional equipment

(grit blasting, airless application) in harbour or during dry docking.

Demand on pre-treatment and painting

To obtain a sufficiently good quality of the painting, the surface must be

thoroughly cleaning and all grease, oil and loose rust scales removed before

painting.

In addition, the thickness of the paint film must not be below the specified

film thickness in order that the resistance against corrosion and mechanical

damages can be sufficient.

Pre treatment and painting will be described in a future section.

TREATMENT BEFORE PAINTING

Before pre-treatment and painting it is important to decide extent and type of

dirt.  The type of dirt determines the cleaning procedure.

Normally the dirt is divided into 4 types:

*  Rust, loose paint, under rust

*  Oil and grease

*  Water-soluble salts such as chlorides from sea water

*  Dust

Rust

Rust is recognised by its well known red colour.  Rust can also occur under

the paint (under rust).  In such cases the paint is blistered caused by the high

volume of rust compared to steel - up to 7 times higher.  Rust has high

porosity and low strength and is therefore unqualified to be coated.

Loose paint

Loose paint is also unqualified for coating caused by poor adhesion.  New

paint on old paint will not increase the adhesion.

Oil and grease

Oil and grease can be caused by oil spillage, leakages and soot drops and in

engine rooms by long exposure of oil aerosols.  This thin oil film will decrease

the adhesion between new and old paint.

Water-soluble salts

When situated under a paint film, water-soluble salts have an osmotic effect

and will absorb water through the paint film resulting in paint blistering.

These salts, normally chlorides (from sea water) and sulphates (from exhaust

gas) in conjunction with water will catalyse corrosion and produce under rust.

Water-soluble salts are clear - up to white crystals and therefore difficult to

observe.  Outside areas on ships will always be covered with salt (sodium

chloride).

Dust

Dust consists of fine particles deriving from many sources:

loading/unloading, fallout from rain, grinding and from the pre treatment.

During application of paint, presence of dust can be a serious problem in

preventing contact between new and old paint and due to its ability of

absorbing acidic components resulting in accelerated corrosion.

Cleaning methods

In the following we shall describe the cleaning methods normally available for

the ships crew.  Cleaning methods as that of wet or dry abrasive blasting and

ultra high pressure hydroblasting, is excluded on board even though the

quality of this cleaning methods is second to none.

Removal of rust flakes

Needle guns: The needle gun is excellent for removal of rust

flakes and  heavily rusted paint layers, especially

on edges.  The surface,  however, will be uneven, so that

grinding will be necessary.

Scraping: Scraping is a good method for removal of porous rust

layers  followed by wire brushing or disc grinding.

Removal of rust: Grinding is one of the best methods when abrasive

blasting is  impossible.

The scheme below gives a survey of the particle size for different tasks:

Task

Quality of

Particl

Grinding

Basis material

Form

grinding

e size

material

Very rough

24

Aluminium

Fibre, heavy

Discs only

Rust and

Rough

40

oxide

quality, open

mill scale

linen, heavy

Medium

60

quality, open

free cut

Paint and

Medium

Silicon-

Paper, heavy

Discs only

Edges

80

carbide

quality, open

Paint in

Fine

Silicon-

Papery, heavy

Discs

good

smooth-

150

carbide

quality, open

rolls

condition

and matt

grinding

Even if the disc material is rubber, uneven surfaces will not be cleaned

sufficiently in the grooves.

Wire brushing

This method will give a better cleaning of prooves than grinding provided that

the brushes are sharp.  Bristly brushes

brushes both in manual and power tools are

ineffective and will polish instead of remove the rust.  Twisted brushes are

the best for power tools.

The common standard used for control of the cleaning quality is Swedish

Standard SIS 055900 (DS 2019).  The cleaning quality must be at least St 1.

Hard metal milling

This methods is excellent for drilling of local pittings and is especially very

suitable for maintenance of cargo tanks.

Degreasing

Water-soluble chemicals

The cleaning agent has to be applied in a suitable concentration depending

on the pollution.  After 10-15 minutes the emulsion has to be removed with

fresh water either by high pressure equipment or by hand.  This method will

remove oil, grease, salts and dust in one operation.

Thinner and cloths

Only clean cloths must be used.  In order to obtain a clean surface the cloths

must be changed frequently.

After degreasing, the rinsing water must not bead on the surface, otherwise

the degreasing must be repeated.

Removal of salts

Surfaces to be painted must always be washed with clean, fresh mater before

painting.  If the surface is heavily corroded, washing before and after removal

of the rust is recommended.  High pressure hosing with fresh water is the

most suitable method.

Removal of dust

If cleaning with water-soluble agents and/or washing with fresh water has to

be done, only remaining dust from the grinding or brushing has to be

removed.  this can be carried out by sweeping or air blowing followed by

wiping-off with (wet) clean cloths.

When the surface does not colour a clean cloth, the surface is clean and

ready for painting.

Weather conditions

Outdoors, the pre-treatment must be considered as an uninterrupted part of

the painting, which means that the weather conditions should be sufficiently

attractive for the paint to be applied immediately after the pre treatment.

Therefore, it is inexpedient to carry out the pre-treatment during poor weather

conditions or if the surface is wet or if the seas are flooding the areas to be

treated.

If paint is applied on a wet surface, the result will be poor and the paint will

peel off.  If paint application is postponed due to poor weather conditions,

the pre-treatment has to be repeated before application, and more than half

of the work will be wasted.  If the relative humidity can be controlled very

simply by sweeping the surface (the surface must be dry) with a wringed

cloth.  If the humidity is evaporated within max. 15 minutes, the surface can

be accepted

APPLICATION

The application of paint must give sufficient covering of the surface,

uniformity and observance of the specified film thickness.

It is a demand that the dry film is without pores, blisters and similar defects.

Methods

Application methods of interest are:

*  Brush application

*  Paint roller application

*  Spraying application

Low pressure:

normally described as pneumatic, conventional.

High pressure:

normally described as hydraulic, airless.

Brush application

Typical brush types for application on steel are flat brushes, round (or oval)

brushes and long-handed brushes.

Flat brushes are especially suitable for large surfaces, while round and oval

brushes are suitable for spot repair of small pipes, bolts etc. and for

application of bare steel primer.

Long-handed brushes are suitable for inaccessible surfaces and can be used

as a supplement to airless spraying.

During application the brush must be placed in a right angle to the surface in

order to make a smooth and even film.

A trained painter will paint relaxed.  A convulsive grasp of a tool may result in

unnecessary and early tiredness.

Round or oval brushes may be ruined at one-sided use, resulting a dog-ears

and complication of the application.  This type of brushes must be rotated

during use in order to wear the brush evenly.

Flat brushes must have long bristles, which will result in a longer life.  This

type is suitable for large and smooth surfaces, if the application technique is

right.  A wrong technique may give a risk of small spots without paint around

bolts, welding seams etc.  On such places an additional application must be

carried out with a 3/4” or 2” long-handed angle-brush.

The paint should be applied on the surface by moving the brush length wise

and crosswise.  Rough surfaces, welding seams, edges and angles should be

given special attention.

After use the brushes have to be cleaned in thinner.

The

advantages

by brush application are the following:

Applicability

Brush can be used for almost all surfaces, is easy to move and will not need

electric power or compressed air.

On thorough application dust and partially the humidity are removed from the

surface.

Cleanliness

The method is clean and demands no or only limited cover.

Good wetting of the surface

On rough and uneven surfaces the wetting and penetrating quality is

comparable with airless application.

Therefore, the brush is especially suitable

for application of first primer coat

The

disadvantages

are the following:

The method is not suitable for all types of paint.  High-build coatings can be

applied in “normal” film thickness only (appr. 40 micron).  Difficulties may

arise by intensive brush application of second or subsequent coats of some

physically drying paints.

Brush application is more slowly than other application methods.

Paint Roller

The paint roller is first of all a fast working tool, but there is a risk for uneven

film thickness and spot wise insufficient covering.

Typical materials for paint rollers are:

Lamb’s wool: Long-piled and therefore preferred for rough and uneven

surfaces.

Mohair: Short-piled and therefore good for smooth surfaces.

Special

lacquer rollers for finishing work exist.

Nylon and Dynel: Hard wearing synthetic alternatives to lamb’s wool and

mohair.

Plast foam: A cheap but unstable material, unqualified for application

on steel and metal.

The lamb’s wool rollers apply the paint in thicker layers than the mohair or

nylon rollers, and therefore the former is used for uneven and rough surfaces

and the latter for even and smooth surfaces.

The paint should be applied on the surface with slow and even movements

up and down and across.  Avoid to drain the roller for paint, in which case

the roller will raise dust of paint.  Do not spread the paint excessively

because of risk of film thickness being below that specified.

The

advantages

by roller application are the following:

Easy to change from place to place and independent of electric power and

compressed air.

More cleanly than spraying.

The

disadvantages

are the following:

Not suitable for application on irregular constructions and surfaces (small

pipes, welding seams, angle irons and bolts).

Paint roller gives a risk of application of thin, uneven layers with many spots

without paint and with pores (pinholes).

Paint rollers give a poor wetting of the surface, and therefore unsuitable for

application of primers on bare steel.

High-build coatings can only be applied in normal film thickness (20-40

micron)

Low pressure spraying (conventional)

During spray painting the compressed air is used for atomisation of the paint

and transportation of the atomised paint to the surface.

A needle valve operated by the gun trigger controls the paint quantity passing

through the nozzle.  The fan angle is controlled by the quantity of air passed

through the “horn” of the gun.

In order to make a proper application by low-pressure equipment the air

pressure must be 1½-4 bar (kg/cm²).  As a rule of thumb for standard paint,

the air pressure in the paint vessel must be 1½-2 bar and the atomisation

pressure 2½-3 bar.

The distance from the spraying gun to the subject must be about 30 cm and

the overlap 10-20 cm.

Special attention must be paid to corners and edges and the places where

over spraying is possible such as the borderline between horizontal and

vertical areas, pipes, profiles etc.

Among the

advantages

of low pressure spraying are:

That application of uniform coats in normal thickness is easy to obtain.

That adjustment of paint consumption and fan angle is simple and quick.

The method is essential quicker than brush and roller application when the

plant is rigged.

The

disadvantages

are the following:

Much spray-dust and therefore waste of paint.

Inexpedient for outdoor application, because wind as well as compressed air

will move the dust.

Poor penetration and therefore inexpedient for application of first primer coat,

especially on rough surfaces.

Insufficient covering of inward covering corners due to return of compressed

air.

Only expedient for application of paint with low viscosity.

Risk of dry-spraying.

Low flexibility compared with brush and roller.

Dependence of power supply (compressed air).

Difficult to clean.

High pressure spraying (airless)

Airless is the most common application method at shipyards and other places

where large steel constructions must be protected against corrosion.

The atomisation arises when during a high hydraulic pressure (100-350 bar)

the paint has to be pressed through a nozzle with very small orifice.

Adjustment of the fan angle and the paint consumption can only be carried

out by changing nozzle.

The high pressure equipment operates by compressed air with a pressure of

5-7 bard.  Long thin air- and paint-hoses must be avoided due to the risk of

block-up.  If long hoses are necessary, the diameter must be at least 3/8”

with the exception of the last 5 meters where the diameter should be 1/4”.

The spraying equipment with a pump ratio of minimum 1:30 and with a

capacity of 6-12 litres/minute will normally apply the paint without thinning.

The pump ratio is the ratio between the paint piston and the air piston.  This

means that if the pump ratio is 1:30 and the air pressure is 6 bar, the

pressure in the nozzle will be 180 bar.  The spraying distance must be 30-40

cm and the overlap between each passage at least 1/6 of the fan width.  The

gun should be held in a right angle to the surface.  Before application, be sure

that the spraying condition is perfect, i.e. without streaks (the pressure too

low), paint-dust (the pressure too high) or other defects.  In order to minimise

paint-dust or local high thickness it must be recommended to shut down the

paint supply in every turning.  The trigger must be activated when movement

in new direction starts.

During low temperature the paint may become so viscous that thinning is

necessary.

The nozzles will be selected according to type of job, but the following nozzle

sizes are all-round for outdoor jobs:

Nozzle size Fan angle

0.021”-0.025” (0.027”) 65°-(80°)

0.017”-0.019” 50°-65°

Great caution must be observed in handling the gun, which works with very

high pressure.  To prevent accidents the nozzle must be equipped with an

approved safety tip guard.  Be sure that the equipment is explosion-proof.

For each type of airless equipment the supplier’s instructions for

ready-making, cleaning and dismounting must be followed.

Extremely good results can be obtained with airless application.  If faults

occur they are normally caused by:

Insufficient pressure (too long or too thin hoses, insufficient

pump  capacity)

Dirty or worn-out paint filter

Worn-out or wrong nozzle.

There are many

advantages

by airless application, and the most conspicuous

are:

Fast working, when the equipment is mounted.

Excellent atomisation without atomised air and therefore small development

of paint-dust.

Easy to obtain a thick paint film.

The only method for application of high-build paint.

Long range by use of extender.

Good penetration and therefore good adhesion of the paint to the surface.

Very suitable for application of primers.

The

disadvantages

are the following:

Dependence on power supply (compressed air or similar).

Limited flexibility compared with brush or roller.

Long time for mounting and dismounting and therefore inexpedient for

painting of small areas.

Adjustment only be changing of nozzle.

Demand for high security due to high pressure.

Weather conditions

Outdoors the paint application must be carried out during attractive weather

conditions and on totally dry surfaces.  The result of painting on wet

surfaces will always be poor whether the humidity is situated on the steel or

between the coats.

Special attention must be paid to condensation, which may occur during

good weather conditions, if the steel temperature is lower than the air

temperature.

The steel temperature might be lower than the air temperature if a liquid on

the reverse side of the steel (tanks, pipes etc.) cools the surface, or if the

temperature of the steel is rising more slowly than for the air (condensation

in the morning).

Normally, the steel temperature must be at least 3°C higher than the dew

point of the air.  The simple test with a wringed cloth described in the part

“treatment before painting” can also be used.

The temperature is very important for a good result.  Painting on heated

surfaces may result in evaporation of the solvent and afterwards dust

spraying.  Under these conditions the film will be poor with many pores.

If the temperature is low, the drying time will belong, and for alkyds the

drying will stop at temperatures below 5-10°C.

Physically drying paint can in principle be applied when the temperature is

below 0°C, but this must be avoided due to the risk of ice on the surface (no

adhesion) and due to extension of drying time.

Preferably, the application has to be carried out at temperatures of minimum

5-10°C or maximum 30-40°C and with the surface completely dry.

During spraying application it is important that the wind is not too strong,

because this will cause unnecessary paint dust and waste of paint resulting

in a high consumption of paint.