7/30/2019 Q & A 3 BGAS

1/8

1) Etch Primers And their Uses.

Etch Primer is one kind of surface Preparation Material which is used instead of

abrasive blasting. Etch primed surfaces will be slightly rough and they will

Provide, key for the succeeding Painting application.

2. Functions &Uses of Solvents.

Solvents form the evaporative part of the drying process. Thins the Paint so it

can be easily applied. Washes out brushes & Equipment. Acts as a degreasing

Agent if approved.

3. Different Types of Surface Preparation.

a. Areas which are inaccessible for mechanical Buffers (Grinding machine) we go

for Hand abrade with Emery paper Grit 80/120/200.

b. Areas very small and for spot repairs we go for Mechanical Power tool

cleaning.St2, St3.

c. Larger areas we go for open site abrasive blasting, depending on the type of

system we go for Sa1, Sa2, Sa2.5, Sa 3.

4. C.P.V.C.

Critical Pigment Volume Concentration refers to the amount of Pigment

contained in paint and how this affects its Characteristics, i.e.

A Paint containing a lot of Pigment and a little Binder will be a Primer or a

Midcoat, will have a good Opacity and a flat finish whereas a Paint

Containing very little Pigment and a lot of binder will have a Poor Opacity but

will carry a high gloss.

5. Preparation of Two pack Paints for Use.a. Plastic paper to be used underneath of paint tins,

b. All dust to be removed.

c. Lid to be opened without damaging of the rim.

d. All sediments at the bottom of the tin are to be mixed by stirring.

e. Solvents or Catalysts to be added slowly and gradually and mixed thoroughly

in paint.

f. Up to 5 Litres Paint may be mixed by Manual, above 5 litres by Mechanical

mixing to get homogeneity.

g. Tin should be covered without Opening.

6. Purpose of B.S.4800.

1. B.S. 4800 Paint Colours for Building Purposes Specifies 100 Colours which

have been selected from the framework of the 237 Colours contained in

2. B.S.5252 It is standardised. B.S.4800 can be used to Identify existing Colours

when Maintenance Painting and is a method by which all manufacturer

Can make exactly the same Colour.

1

7/30/2019 Q & A 3 BGAS

2/8

7 Qualities of Polyurethane Finish Coats.

Polyurethane coats have a finish which is of High Gloss) they are abrasion

resistant, c) Polyurethane coats can be cleaned easily well resistant to UV.

8. Advantages &Disadvantages of Epoxy Paint system.

Epoxy coatings are one of the strongest Binders. They provide High Build

coating suitable for Airless Spray Application. They can be modified form for

High Temperatures and Damp surfaces, Disadvantage. Epoxy coatings will

make a Poor finish coat because they will chalk easily.

9. Detail operation of Airless & Conventional Spray System?

Airless System works by Pumps (pneumatic/Electrical) which pressurize the

airline Paint at high pressure hoses to the spraying gun. The high pressure

paint which comes out through the small orifice of the gun hits the air and

atomizes, which produces good/efficient patterns 30 times more efficient than

brush. This method is suitable for applying paint to very large areas, it produce

very little overspray, has a large spray pattern and applies a thick coating at one

application.

Conventional Spray- the mixture of air and paint comes out of the gun, at lowpressure and get atomize due to the sudden fall of pressure. Conventional Spray

set ups operate at relatively low pressure so are only suitable for applying

relatively thin materials. In addition they hold only small quantities of paint so if

applying large areas constant refilling of the container would be required. Also

the Gravity Suction versions only be used with the gun in an upright position.

10. Action taken when coatings are applied out of Sequence.

Stop the job. Inform the Engineer or Clients representative. If a wrong type of

paint is applied as primer, it must be blasted off and the system shouldBe started correctly. If the applied primer is ok, start the system from where the

error started and apply the correct system.

11. Risk Assessments when Blast cleaning & Painting.

A) Fire Risk due to Inflammable nature of substances of paint.

B) Fumes &Inhalation of Toxic gases

C) Heat from the Sun

D) Working in confined space

E) To obtain work permit for the job. To use appropriate P.P.E .To Display

boards. Barricading the Area. To have a Fire watcher.

2

7/30/2019 Q & A 3 BGAS

3/8

12 .Probelms When Density & Viscosity of paint are not correct.

a) Poor opacity

b) poor Gloss & slow drying,

c) Poor durability.

d) Paint not be applied to the defined D.F.T. Drying problem may occur. It may create

the surface defects like Runs, Sags or Thixotropic points

. .

13.Visually examine the surface i.e. the Substrate prior to blasting for any

inherentdefects or detrimental contaminants such as oil. Mud etc.

Check blast cleaning air i.e. compressor feed air is free from traces of oil or water.

Check the oil traps are functional.

Observe the surface for unusual discoloration;

Check the abrasive being used for size and for dryness.

Measure the surface profile .whether the prepared surface meets the standard.

Surface profile pattern. Look for unblasted areas.Make scotch test to ensure that the surface is free from dust particles.

a. On Dry Paint films- a) Uniform in appearance b) Free from Paint Faults

c)Missed & skipped areas d) low DFT areas e)no grit sand embedded on the

paint film surface

14.Sequence of Events leading to Clients Inspection

a. Their reasons are mainly due to malpractices of contractor personals and also in

the lapse of the painting Inspector responsibility.

b. Surface preparation is very important, may not been carried out as perrequirement. Could be contaminants present like oil, grease, &dust.

c. Painting carried out in adverse weather conditions.

d. Application of subsequent coat without previous coat not fully cured.

e. Coating intervals not adhered.

f. Skipping or missing out a coat

g. Use of jelled paints. Paint shelf life expired.

h. Not following the coating system sequence.

i. Materials used are not the approved ones& doesnt meet the specification.

15). Factors which cause poor adhesion of Paint system;.

a. Surface preparation is poor.

b. Surface containing detrimental contaminants

c. Overpowered Burnished areas,

d. Surface Profile very less

e. Over thinning of Paints

f. Paint applied over rust or unprepared areas

g. not proportionately mixing of Two Pack Paints.

3

7/30/2019 Q & A 3 BGAS

4/8

16 . Profile Reduction a)If the profile of the blasted surface is very much higher than

the specified range to overcome it while on job corrective action to overcome are

1. Change the blasting Nozzle i.e. from a Venturi goes for straight bore.

2 .Reduce the Abrasive Size.3.Increase the distance between the Substrate and the

Nozzle.

17. Purpose of Working to Quality plan-

a) Setting out specific Quality practices achieve the desirable Quality to meet the

Specification requirements, following the various stages of inspection at every

stage ensuring that each activity is performed aiming at quality ,doing things

rightly at the first time .To follow I.T.P.

18. Recording of information following Project Completion.

a. To have record of work stoppage due to adverse weather conditions (down time)

b. to have record of Materials consumed.c. Manpower deployed and Equipment used.

d. Record of wastage material.

e. Estimation of project cost for future tendering purpose.

19. Advantages of Epoxy coating system

aOne of the strongest Binder available)They provide High build coating suitable for

application by airless spray b)They can be used in modified form for

High Temperatures and Damp surfaces Limitation 1 Epoxy coating will make a

poor finish coat because they chalk easily.

20 Client/ Contractor Relationship. - Good working relationship helps to resolve

problems. To arrive at an amicable s Solution. To express Concern, practical

b. Difficulties and work related problems to resolve. To ensure safe working

methods are adopted. Co-ordial relationship will contribute to understand the

job more precisely.

21). Rust Inhibitive Properties of Paint System-

To protect the piping by the use of rust inhibitive primers which have the chemical

Properties to retard corrosion.

22). Use of Electro static Spray System-

This method of Spray paint application needs a Special Spray gun which applies a

charge to the paint particles.

The Substrate is positively earthed and the paint particles are given a negative

charge at the tip as they leave the gun. The result is that the Paint particles which

are drawn to the earth can wrap themselves completely around small

tubular components, an even thickness coating is

4

7/30/2019 Q & A 3 BGAS

5/8

Obtained and there is little Wastage through Overspray. This Equipment is very

expensive to purchase.

23).Functions of Primers, Midcoats, & Finish Coats.

Primer- To provide maximum lasting adhesion to a substrate for the next paint

layer and retard corrosion.

Midcoat- Barrier to prevent the passage of Water.

Finish Coat Gives Final appearance, degree of gloss & colour. Resistance to

abrasion, UV rays, Weather .To aid the flow from the surface of the metal.

24) Barrier & Sacrificial Coating.

a.Barrier- This isolates the substrate from the environment by means of a low

Permeability coating system. This type of system is usually made up of from

around four coats and contains an M.I.O. which helps give the paint system its

low permeability.

b.Sacrificial- This involves making appoint whose pigments particles

(ZINC/ALUMINIUM) are less noble than the steel onto which it is coated.

The result is that the less noble coating will sacrifice (Anode) itself to the morenoble steel (cathode)

25)Paint FILM TESTING

a. Salt Spray Box- Marine Condition

b. Water Soak Test- Film Permeability

c. Tropical Box - High Humid Environment.

d. Temperature Cycling- Film Flexibility.

e. Cold Check Testing- Low temperature contraction cracking

Practical

1). Checks & use of Whirling Hygrometer.

a. It turns freely.

b.Chamber contains distilled water.

a. Bulbs-Figures are clear (Readable).

b. Fluid is intact and Continuous. Bulb is not cracked.

C.Cotton Wick-a) clean b)Not Frayed c) Covers Wet Bulb d) Must be Wet.

1.Procedure:-

a.Hold the Hygrometer Straight facing the Wind direction. In the Wind

direction and start rotating to 30 -40 rotations per second.

b.First read the wet bulb temperature immediately then the dry bulb

temperature.

2.Repeat the operation to get two consecutive readings within 0.2 c

5

7/30/2019 Q & A 3 BGAS

6/8

Calculate using Dew point calculator for RH &DP.

2).Calculation of Dew Point and Relative Humidity.

For Dew Point- Set dry bulb temperature to wet bulb temperature and read in the

window against the Wet bulb for Dew Point.

For RH %- Dry bulb temperature set to dew point temperature. Look in the

Window for RH %.

3). Environmental Limits for Paint Application

a. The Air or Metal Temperature is at least 3 c above the Dew point Temperature

b. The Relative Humidity is less than 90%.

c. The Temperature for Application is Within the Manufacturers given limits.

4). Identification of Abrasives.

a) Look for what the material is.

b) Observe for things contained in it.

c) Check whether it is used one or not, whether it is grit /shot.

d) Proportion in which it is mixed.

e) Look for spent abrasives- contaminated one. A) Copper slag B) Garnet

C) Shot Grit D) Used ones.

5).Identification of Rust Grades &Blast Cleaning Grades.

Rust Grade - A - Covered in Mill scale with little or no rust

B - A Mixture of Mill scale and rust.

C - Mill scale gone, rusted with slight surface pitting.

D - Heavily rusted and pitted.

Blast Cleaning Grade- Sa 1 - Light Blast Clean

Sa 2 - Thorough Blast Cleaning.

Sa 2 - Very Thorough Blast Cleaning.Sa 3 - Blast Cleaning to Visually Clean Steel.

6).Calibration of Dial Micrometer.

Clean the anvil tip by paper. Ensure that there are no Dust particles in the Jaws

of the micrometer. Release the top screw.

Make rotations to check against readings. When it is done, set the Zero to the

Needle point where it indicates and fix it.

Then take readings. It is precisely what is shown in the Micrometer. Deduct 2

mils for Mylar thickness from the reading observed.

6

7/30/2019 Q & A 3 BGAS

7/8

7). Selection of Comb Gauge & Reading of it.

When a Comb is selected for the range for the thickness will be obtained from

the Specification. This thickness should fall in the centre of the teeth as this

should eliminate the possibility of an error in reading..

Reading of W.F.T. Comb Gauge- WFT is pushed firmly into the wet paint so

that the outer most teeth make contact with the substrate.

Held at right angles to the Surface. Gauge is removed and the teeth are

examined. WFT lies between the last tooth i.e. Coated and the first

Tooth that is Uncoated. Midpoint between this is WFT.

8). Limits for Testex Tape

For 20 to 50 microns, use Coarse 0.8to 2.0 mil

For 40 to 115 microns, use X-Coarse 1.5- 4.5 mil.

9) .Reduction of a Blast Cleaned Surface.

If the blasted surface has the profile more than the Specified i.e. higher range

then to have less value opts for 1.Change the Blast Nozzle Type.

2. Reduce the Abrasive Size. 3. Increase the distance between the substrate and

the nozzle.

10). Principle for Use of Banana Gauge. Narrate the steps for Calibration of Banana

Gauge.Must have a Ferrous Substrate and a non-ferrous coating. Works on magnetic

principle.

Calibration of Banana Gauge.

1. Choose a magnetically insulted shim of known thickness, close to the

thickness of the paint you expect to find.

2. Place the shim on the same substrate surface finish as the surface finish on

which the paint film to be measured is attached, e.g.-if the paint

Is on a blasted surface, calibrate the gauge on a uncoated Blasted surface.3. Place the magnet onto the shim and press firmly on the instrument, Wind the

scale wheel forwards (away from you).Until the Magnet is

Definitely attached to the shim substrate.

4. Gradually wind the wheel backwards slowly until the magnet detaches itself.

T At this point, move the cursor on the instrument to the

thickness of the shim as shown on the Scale wheel. With some instrument the

scale itself must be moved to line up with a fixed cursor.

When using the later type of instrument .rotate the wheel to zero to locate the

position of the scale adjuster.

7

7/30/2019 Q & A 3 BGAS

8/8

6. The instrument is now calibrated and may be used to measure the D.F.T of

any non magnetic paint films to a claimed accuracy of

8