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Why Paint?

Paint is a surface coating, which decorates and protects the surface on which it is applied.

No paint is good if applied improperly. This is borne out by the fact that paint in the real sense is not a finished product. The consumer requirement is deemed to have been met only when the liquid paint is applied on a surface and the film is formed, i.e. the paint dries. The aforesaid factors influence the realization of the consumer’s requirement.

In architectural finishes, the decorative angle occupies a prominent position but the protective properties also play their role silently. In case of paints for heavy-duty applications like, at chemical refineries, marine environment, fertilizer plants etc., protective aspect is more important.

The success or failure of any coating is influenced by the following factors.

Substrate Condition

Surface Preparation and method of application

Environmental conditions at which the paint is applied and expected to withstand during service.

The quality of paint used.

There are four prominent types of surfaces, which are painted regularly, for protection as well as for beautification. These are:

Metal (Ferrous & Non-Ferrous)

Concrete / Masonry

Plastics

Wood

There is a need of specific coating to the each surface mentioned above. This book elaborates the paint, the need of painting, surface preparation, and various properties of paints. It also comprises various application methods adopted to apply paint along with the defects observed during and after painting.

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What is paint?

Paint can be defined as a fluid material which, when spread over surface in the form of a thin layer, will form a solid, adherent and cohesive film.

Some paints are also available in the form of powder. They are either converted to fluid form by addition of suitable thinner prior to its application (e.g. Dry distemper, Cement Paints, Powder Coatings etc.) or applied directly. The fluid or liquid paint consists of four major ingredients.

P i g m e n t s R e s i n T h i n n e r o r S o l v e n t A d d i t i v e s

P A I N T

Pigment, binder or film former or resin or vehicle and solvent or thinner and the relative properties of these ingredients can be varied to produce films with any desired physical and application characteristics.

Properties of Pigments :  Colour  Opacity  Tinting Strength  Light Fastness  Resistance to Heat  Resistance to Chemicals  Corrosion Inhibition  Barrier Effect

e.g. – TiO2, Carbon black, chrome pigments, metallic pigments, oxide pigments, barites, calcite, china clay etc.

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Properties of Resins :  Film Formation

 Adhesion with Substrate  Corrosion resistance  Chemical resistance  Water resistance  Gloss

e.g. – Epoxy, Polyurethane, Chlorinated Rubber, Nitro Cellulose, Acrylics, Alkyds etc. Properties of Solvents :  Flow  Applicability  Resistivity  Drying

e.g. – Xylene, M.T., Butanol, Toluene, Acetates etc. Properties of Additives :  Drying  Gloss  Anti Settling  Anti Skinning  Anti Floatation  De-Foamers etc.

e.g. – Driers, anti-settling, anti-skinning, de-foaming etc. Properties of Paints :

Wet Paint Properties o Fineness of grind o Viscosity

o Weight per liter

o Percentage solid contents o Percentage volume solids o Medium separation

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o Drying properties o Covering capacity o Thinner intake o Flash point o Shelf life  Dry Film Properties

o Hiding o Gloss

o Scratch hardness o Flexibility & adhesion o Impact resistance o Salt spray

o Chemical resistance o Water immersion Testing of paints :

Property Testing Instrument

Wet Paint Properties

Fineness of grind Hegman Guage

Viscosity / Consistency FC B4 / Stormer

Weight per liter Weight per liter cup

Percentage solid contents Oven & balance Percentage volume solids Oven & balance

Thinner intake Measuring cylinder

Drying Drying time recorder

Covering capacity Morris Chart & Kryptometer

Flash point Able’s cup

Shelf life Incubator

Dry Film Properties

Film thickness DFT Meter

Hiding Morris chart

Gloss Glossometer

Hardness Pencil & Scratch hardness tester

Impact resistance Impact tester

Abrasion resistance Taber abraser

Flexibility Mandrel

Adhesion Tape test

Resistance to chemicals / corrosion /

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SURFACE PREPARATION

I n t r o d u c t i o n

Surface preparation is a backbone of any given coating system. Most of the

paint performances are affected by contaminants like loose mill scales, rust, oil, grease, dust, dirt etc. It is very essential to remove these contaminants before paint application.

C o m m o n M e t h o d s o f S u r f a c e P r e p a r a t i o n

1. Abrasive Blast Cleaning 2. Manual & Power tool Cleaning 3. Water Jet Cleaning

4. Wet Abrasive Blast Cleaning 5. Chemical / Solvent cleaning

There are various grades & standards of surface preparation. These standards are self-sufficient and give better idea of the degree of surface cleaning.

Selection of surface preparation method depends and varies as per the substrate condition, nature of substrate and performance requirement of the coating systems. Based on this, surface preparation methods can be divided into two categories. 1. Primary Surface Preparation: - Surface preparation prior to painting of new metal or concrete, which includes removal of rust, oil, grease, dust, foreign matters, dirt etc before application.

2.Secondary Surface Preparation: - Surface preparation prior to maintenance coatings sort of jobs, which includes removal of rust, Zn corrosion products, loosely bonded old coating, scuffing of old intact coating, removal of oil, grease, dust, dirt, foreign matters.

1 . A b r a s i v e B l a s t C l e a n i n g

Abrasive blast cleaning is a best method to prepare surface, and to achieve longer protection. Appropriate blasting method in combination with proper coating system can give enhanced protection of any given surface.

In this process, abrasives like sand, steel shots, grits or slag are directed to the surface with a very high pressure, thus, removal of rust, mill scales, loosening the bondage of previous coating takes place. Thus creating an anchorage or profile for the paint to adhere to.

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There are number of institutions which have documented blast cleaning methods and are best guide to the surface preparation. These are summarized as follows:

SSPC Swedish Standards

BS NACE ISO Description

White Metal (SSPC–SP5) Sa 3 1 st Quality NACE 1 Sa 3 Removal of total rust, mill scales, foreign matters, dust, dirt etc. to have original metallic sheen. Near White Metal (SSPC-SP10) Sa 2½ 2nd Quality NACE 2 Sa 2½ Removal of rust, mill scales, foreign matters, dust, dirt, grease etc. 5% of total area can be left over with old coating, rust/mill scales in pits. More practical method. Commercial Blasting (SSPC-SP6) Sa 2 3rd Quality NACE 3 Sa 2 Removal of mill scales, rust, oil, grease, dust, foreign matter etc. Tightly adhering old coating can be left over. Brush off Blasting (SSPC-SP7) Sa 1 - NACE 4 Sa 1 Light blasting to create profile.

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2 . H a n d & P o w e r T o o l C l e a n i n g

When blasting is not practical, hand and power tool cleaning is employed. Sometimes, in routine and localised jobs, hand and power tool cleaning is preferred over blasting, because of easy access to crevices, joints, angles, restricted areas etc. Following methods and tools are used to clean the surface with this procedure.

 Wire brushing: - Wire brushing is a conventional method not suitable for the removal of mill scale, but suitable for the preparation of weld seams. The main disadvantage is that the treated surfaces are often not completely freed from the corrosion products.

 Chipping: - Chipping is usually done in combination with wire brushing. It is suitable for local repairs with conventional or some specific paint systems. It is not generally recommended for preparation of surfaces to be coated with epoxy or chlorinated rubber paints. It is very useful in removing thick rust scale which economizes in later blasting operations.

 Impact cleaning tools

 Rotary cleaning tools

 Rotary impact cleaning tools

There are two standards for hand & power tool cleaning, which are documented by Swedish Standards & SSPC. Both standards give exact idea of the degree of surface preparation by Hand tool or Power tool.

Cleaning Method Swedish Standard SSPC

Hand Tool St 2 SSPC - SP2 Power Tool St 3 SSPC - SP3

3 . W a t e r J e t C l e a n i n g

Water jetting uses water of sufficient purity and quality at high or ultra high pressure to prepare a surface for re-coating. It can be used to clean steel, non-ferrous metals and other hard surfaces. It generally removes loose paint, chemical contaminants, loose rust and scale, grease and other materials not tightly bonded to the surface.

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Four types of surface preparation using water are given below.

 Low pressure water cleaning: - Cleaning performed at pressures less than 5000 psi

 High pressure water cleaning: - Cleaning performed at pressures from 5000 to 10000 psi

 High pressure water jetting: - Cleaning performed at pressures from 10000 to 25000 psi

 Ultra high pressure water jetting: - Cleaning performed at pressures above 25000 psi and above

Water jet cleaning is very effective for cleaning irregularly shaped surfaces such as valves, flanges and gratings. Where abrasive blasting is not feasible, water jet cleaning can be an effective alternative. Water jetting will not produce an etch or profile of the magnitude produced by abrasive blasting, rather, it exposes the original abrasive blasted surface profile if surface was blast cleaned during previous painting.

Water jet cleaning can be destructive to non-metallic surfaces. Soft wood, insulation, electric installations and instrumentation must be protected from direct and indirect water jet. Generally, municipal water satisfies the purpose. Seawater or hard bore well water is not to be used, as it leave salt on the surface after cleaning. Water used in water jetting must be clean and free of erosive salts or other contaminants that damage pump valves or leave deposits on the surface being cleaned.

4 . W e t A b r a s i v e B l a s t C l e a n i n g

Wet abrasive blasting may be performed with low or high pressure fresh water to which a relative small amount of abrasives is introduced, and in some cases inhibitors are added to prevent flash rusting (however, as a general rule, it is recommended not to use inhibitors when cleaning areas are to be immersed during service). This reduces the amount of airborne dust and sand. It is necessary to rinse the surface after blasting to remove sand and debris.

5 . C h e m i c a l / S o l v e n t C l e a n i n g

This process involves cleaning of surface with the help of paint strippers, solvents, acids etc. This method, although very effective to remove oil, grease, old coating, is not good at removing mill scales, rust and corrosion products. This process is implemented mainly in OEM industries.

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S u r f a c e P r o f i l e

Besides degree of cleaning, surface profile is an important aspect in surface preparation. The dry film thickness of coating should be at least three times the surface profile to give long lasting protection.

S u r f a c e P r e p a r a t i o n f o r N o n - F e r r o u s M e t a l S u b s t r a t e s

Surface should be dry and clean. Any visible oil/grease should be removed by thinner / solvent wiping. Cleaned surface should be abraded or sweep blasted using low pressure and non-metallic abrasives, then primed with a coat of GP Prime 401 etch primer.

G a l v a n i z e d S t e e l

Degreasing is to be carried out to remove any oil/grease. Any white zinc corrosion products should be removed by high-pressure fresh water washing or fresh water washing with scrubbing. Even if sweep blasting is done, water - washing is recommended to ensure removal of soluble zinc salts.

C o n c r e t e a n d M a s o n r y S u r f a c e s

 N e w c o n c r e t e o r m a s o n r y :

Must be allowed to cure at least 30 days before coating. The moisture content of the concrete/masonry should be less than 6%. In case of large areas and for severe exposure conditions, the surface has to be prepared by light blasting. In less critical areas where blasting is not practical, wire brushing has to be adopted to remove laitance, followed by treating with dilute HCl (10%).

 O l d c o n c r e t e s u r f a c e :

The surface has to be prepared by light blasting preferably. In case, blasting is not practical, etch the surface to get a good surface profile with dilute HCl (10%) etching followed by thorough rinsing with fresh water to remove all the free acid. Remove the surface contaminants like grease, oil etc. by solvent wiping or by 10% caustic solution. Any soluble salt is required to be removed by water washing.

Remove acid and contaminants by liberal wash with water. Ensure that acid solution does not remain on the surface and joints. Allow the surface to dry thoroughly before applying GP Prime 100/200. Any cracks should be cut out and filled with suitable filler prior to painting.

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PAINT APPLICATION

Proper application is a critical part of the paint system. The choice of the application method is dependent on various factors such as type of coating, performance, handling ease, speed, size and shape of substrate, location, final appearance and economy.

The proper use of the application tool or equipment used to apply the paint or coating can have a definite effect on the time required, the appearance of the finished job and the performance of the applied product.

The following methods of application are normally employed for high performance coatings:

1 . B r u s h A p p l i c a t i o n

Brushing is the most common method for applying coatings. While brushing is a somewhat slow procedure many small jobs do not warrant the use of any other application method. Brushing is especially useful for touch up work, spot priming, stripe coat or work in confined areas, where spraying is impossible. Less paint is wasted when applied by brush than by other methods. Use cross application to minimize brush marks and generally do not apply DFT greater than 100 µ in single coat to avoid sagging.

Either natural or synthetic bristle brushes are suitable for use with “solvent based” coatings. Synthetic bristle brushes are preferred with “water based” coatings because natural bristles tend to swell in water.

2 . R o l l e r A p p l i c a t i o n

Rollers are efficient tools for applying industrial coatings and are suited for broad flat surfaces. The general rule for selecting a roller cover is “the smoother the surface the shorter the nap”. Solvent thinned coatings should be applied with either lamb’s wool or synthetic covers and water-reduced coatings should be applied with synthetic covers. When using rollers to apply coating systems such as epoxies, polyurethanes which contains strong solvents, be sure that the roller cover selected is constructed with glues which are resistant to these strong solvents.

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3 . S p r a y A p p l i c a t i o n

The easiest and most rapid method for the application of protective coatings to large areas is spraying. Spray application is preferred where a smooth uniform finish is desired and speed of production is important.

Conventional air atomization is used when quality of finish is of utmost importance or where great versatility is desired. Airless spray is best for large-scale

operations not requiring very fine finish.

Both conventional and airless spray may be modified for increased performance or for specialized applications. One such modification includes adding heaters to fluid lines. The use of heated paint permits atomization at lower pressures, decreases or eliminates the need for thinning, cuts down on over spray rebound and provides a heavier film build with minimum waste of paint and solvents. The only drawback associated with hot spraying is that the pot life of catalyzed products sprayed by heated method is generally reduced.

A i r S p r a y A p p l i c a t i o n :

A conventional air spray gun is a precision tool, which uses compressed air to atomize sprayable materials. Air and paint enter the gun through separate passage and are mixed and ejected at the air nozzle to provide a controlled spray pattern. The amount of paint leaving the gun is controlled by the pressure on the fluid container, the viscosity of the paint, the size of the fluid orifice, and by the fluid needle adjustment.

Suggestions for effective air spray painting:

 Use the lowest possible air and fluid pressure when operating a spray gun.

 Use the proper fan width for the job.

 Spray from the proper distance (15 - 25 cm)

 Hold the gun perpendicular to the work throughout the spray stroke.

 Move the spray gun parallel to the work surface throughout the spray stroke.

 Move the spray gun at a speed, which assures that a full wet coat is applied to the surface.

A i r l e s s S p r a y A p p l i c a t i o n :

Airless spray is a method of application, which does not directly use compressed air to atomize the coating sprayed. Hydraulic pressure is used to atomize the fluid by pumping it at high pressures through a small precision orifice in a spray nozzle. As the fluid is released at these high pressures, it is separated into small droplets resulting in a finely atomized spray.

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Airless spray painting is cleaner and faster than conventional spraying methods. One advantage of airless spraying is that the over spray fog or rebound associated with conventional spray is greatly reduced. This makes use of equipment possible in places and applications where material formerly had to be brushed.

Another significant advantage of airless spray is the ability to apply heavy coating thickness more quickly than by any other method. Most coating materials may be sprayed in their unthinned state that also helps contribute towards the formulation of high build coatings and greatly reduces thinner use.

S u g g e s t i o n s f o r e f f e c t i v e a i r l e s s s p r a y :

The technique employed for airless spraying is similar to the technique practiced in air spraying.

 The ideal spraying pressure for any given tip is achieved by gradually increasing the pressure until the spray pattern appears uniform across its fan width and the atomized coating particles are of acceptable size.

 If the coating is coarsely atomized, the pressure may be increased slightly, a smaller orifice tip used or the coating thinned.

 Avoid using excessively high airless spray pressures, which may cause effervescence or other finish defects.

 Holding gun perpendicular and move it parallel to the surface at all times in order to obtain a uniform coating of material.

 Arcing, heeling and toeing should be avoided at all times.

 The proper working distance with airless spray is approximately 25 - 30 cm.

 When using wide-angle spray tips, the gun must be moved closer to the work. Excessive spray distance increases paint fog and paint consumption.

The lifetime of any protective system is determined by the dry film thickness of the paint system. Particular attention should be given to the thoroughness with which the coating is worked into crevices, weld and rough surfaces. Special attention should be given to sharp edges to ensure that they are covered with an adequate coating thickness, if required use an additional touch up coat / stripe coat at these areas to attain a minimum system thickness.

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PAINT CALCULATIONS

1 . E s t i m a t i n g P r a c t i c a l C o v e r a g e

To calculate practical coverage capacity at the recommended dry film thickness, the following variables must be known:

a. % Volume Solids

b. Actual dry film thickness (DFT) c. % Loss Factor

The material loss factor depends upon a number of factors, viz :

I. Application method, where conventional spray application gives maximum losses.

II. Geometry and shape of the substrate like irregular and complex shapes of surface.

III. Nature & texture of the substrate like porous and absorbent surfaces. IV. Skill of operator

V. Working condition like wind flow, temperature etc.

VI. Physical losses such as left over in drums, unused portion after completion of pot life, cleaning losses etc.

Once these variables are known, use the following formula to make the calculation:

p.c.c. %Volume Solids x 10 Actual DFT x 100 - % Loss Factor 100            

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2 . E s t i m a t i n g C o s t o f p a i n t s p e r S q . M .

To calculate the material cost per Sq. M., the following variables must be known: a. Price per liter of paint

b. % Volume solids

c. Dry film thickness (DFT)

d. % Loss factor (or practical covering capacity)

Once these variables are known, use the following formula :

Material Cost per Sq M Price per Ltr T C C x 100 100 Loss Factor . . . %             

Where, T.C.C. = Theoretical Covering Capacity in m2/Ltr.

T C C in Sq M Ltr Volume Solids x 10 DFT . . . ./   %     3 . E s t i m a t i n g Q u a n t i t y o f P a i n t r e q u i r e d f o r a j o b

To calculate the quantity of paint required for a given job, the following parameters must be known:

a. Area of the job in Sq. M. b. % Volume Solids

c. Dry film thickness (DFT) d. % Loss factor,

Once these parameters are known, then use the following formula:

Quantity of Paint in Ltrs Area T C C x 100 100 Loss Factor . . . %             

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PAINT DEFECTS

Sr

. No

Coating

Defect Possible Causes Cures

1. Paint

detachment / delamination

 Intercoat contamination

 Over coating intervals too long

 Too thick coat

 Detachment from base itself

 Check compatibility of paint

 Follow over coating interval as specified

 Check DFT

 Stop water seepage and fill up the cracks, check surface for contaminations 2. Dry Spray /

Cob webbing  Poor application, i.e.higher, too wide spray fan, excessive pressure

 Excessive application temperature

 High wind velocity

 Correct spray techniques / factors

 Allow the surface to cool down

 Provide wind shield, stop painting

3. Poor Opacity  Low dry film thickness

 Lower viscosity

 Wrong selection of undercoat

 Settled pigment may not have been thoroughly mixed

 Apply additional coats to build DFT

 Increase application viscosity

 Select appropriate undercoat

 Stir sufficiently and agitate paint before use.

4. Lifting  Uncured/wet undercoat

 Undercoat sensitive

 Allow proper curing of each coat

 Use tie coat

 Select proper system 5. Cissing  Contamination like

moisture, grease, overspray of other paints etc.

 Clean surface prior to painting

 Sand the affected area and repaint

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6. Pinholes  Poor application technique holding spray gun too close, high air pressure

 Improper surface condition

 Substrate

contamination like, oil, water, dirt etc.

 Correct spray techniques factors

 fill up the imperfection

 Clean the surface of all contaminants prior to painting

 Fill the pinholes with more material by brush / additional thin coat of paint.

7. Poor Drying /

Soft Paint  Adversecondition painting 

Ensure good ventilation and apply at suitable temperature and humidity. 8. Blistering /

Solvent Popping

 Excessive film thickness

 Entrapment of solvent or air beneath the paint film.

 Apply at recommended DFT

 Allow the film to cure sufficiently.

9. Orange Peeling  Very fast evaporation of solvents

 High spraying viscosity

 Too high DFT

 Follow the correct spraying technique

 Reduce spray viscosity

 Apply at recommended DFT 10. Mud Cracking  High film build

 Over atomization

 High temperature condition

 Apply at recommended DFT

 Proper equipment set up

 Slow evaporating thinner or reschedule wash to favourable temperature conditions.

11. Poor Gloss  Sinkage into porous substrate or insufficiently dried undercoat

 Low dry film thickness

 Selection of wrong thinner

 Use appropriate undercoat or filler

 Apply higher DFT

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SAFETY INFORMATION

The majority of paints, coatings and thinners do not present special hazards in storage or use provided that good standards of industrial hygiene are maintained. However, it must be remembered that these materials can introduce two potential hazards - health and fire.

1 . H e a l t h H a z a r d s :

Paints, coatings and thinners are mixtures of various chemicals, some of which are potentially hazardous if their use is not strictly controlled in accordance with good standards of industrial hygiene and safe working practice.

The following is a guide to the potential hazards and recommended safe practices.

I n g e s t i o n :

The ingestion of paint should be avoided. Food and drink should not be brought back into, stored, prepared or consumed in areas where paints are stored, handled or used. Smoking in such areas should be prohibited.

In the event that paints, thinners etc., are accidentally swallowed, do not induce vomiting. Seek immediate medical advice.

I n h a l a t i o n :

The inhalation of paints, dust or fumes should be avoided by the use of local ventilation or extraction. Where fumes or dust are unavoidable, suitable approved respirators or facemasks should be worn.

Remember that solvent vapours are heavier than air and will tend to accumulate at the bottom of tanks or in confined spaces. Never enter areas where this could have happened without wearing suitable breathing apparatus. If dizziness, drunkenness or headaches are experienced, solvent vapours could cause these - move immediately into fresh air and do not return until the area has been declared safe. Where necessary, gas tests should be carried out in confined areas or areas that are difficult to ventilate effectively. If anyone should overcome fumes, carefully remove him/her to fresh air - allow recovering gradually and seeking immediate medical assistance. In areas where the ventilation is poor, an airfed mask hood is essential. If any doubt exists, wear an air fed mask hood.

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S k i n C o n t a c t :

Normally harmless chemicals can cause irritation by repeated or prolonged contact with skin and, in extreme cases; there is a risk of dermatitis. All personnel who handle and use paints should wear appropriate protective clothing (as a minimum; gloves, eye protection and aprons). Splashes of paint on the skin should be treated promptly by copious washing with clean water, or an approved cleansing agent.

E y e P r o t e c t i o n :

It is recommended that operators should wear suitable eye protectors when there is a risk of paint splashing into their eyes.

Splashes of paint into the eyes should be treated promptly by copious washing with fresh water for at least 10 minutes. It is a sensible precaution to seek medical advice.

P e r s o n a l H y g i e n e :

All personnel involved in the handling and use of paints should be encouraged to observe the highest standards of personal hygiene. Suitable protective clothing should be supplied and maintained and adequate facilities for washing provided. In the event of clothing becoming soiled with paint, it should be changed and the affected area thoroughly washed with soap and water. Personnel should be encouraged to wash especially before eating food.

2 . F i r e & E x p l o s i o n H a z a r d s :

With the exceptions of solvent-free and water-thinned materials, all paints contain organic solvents which are flammable to a greater or lesser degree.

Users of paint and related products should make themselves aware of their statutory duties with regard to national regulations, and seek advice from Government Agencies, if in doubt.

The main points to observe are:

 Storage and usage should be in separated areas, constructed to the appropriate standard of fire resistance. The quantity of materials stored in the actual working areas should be as small as is practicable.

 Adequate ventilation and extraction should be provided and maintained.

 Adequate fire prevention and fire fighting equipment should be provided and maintained. Do not attempt to fight fire with water - this

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 Fight fire with dry chemicals, foam or carbon dioxide extinguisher.

 All possible sources of ignition should be strictly controlled, e.g. electrical equipment, metal-to-metal sparks. Smoking should be prohibited in areas where paint materials are used, stored or handled.

 In the event of a fire the possibility that poisonous fumes may be emitted must always be recognized - if in doubt, use breathing apparatus.

References

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