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CVA106 > Paints > Flashcards

Paints Flashcards

1
Q

Why might paint be used

A

-Prevent deterioration of materials
-Decorative
Easily maintainable surface
-Provide light/heat reflecting properties
-Prevent metallic corrosion
-Electrically conductive paints
-Intumescent paints of fire protection

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2
Q

5 Constituents of paint

A
  1. Vehicle
  2. Binder
  3. Solvent/Thinner
  4. Pigments
  5. Additives
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3
Q

Role of the binder

A

The part that holds together the pigments and other chemicals. Converts from a liquid coating to a hard elastic skin that provides resistance

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4
Q

Role of the solvent/thinner

A

The solvent dissolves the resinous constituents, whereas the thinner (a blend of different solvents) is used to dilute the already dissolved resin

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5
Q

Name 4 additives and their role

A
  1. Driers, added to oil based paints to give out oxygen and therefore increase the speed of drying
  2. Plasticisers, make the hardened film more flexible
  3. Light Stabilisers, make colour more stable under sunlight
  4. Insecticides/Fungicides, prevent attack by insects and the formation of mould
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6
Q

What 2 factors affect film formation and why

A
  1. Temperature, less than 4C reaction is slow and can impair film formation, above 35C water base paints may lose their water before solids have had a chance to coalesce
  2. Humidity, excessive humidity prevents evaporation of water, too low and it may prevent a chemical reaction that is dependent on water vapour
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7
Q

Components of typical paint systems

A
  1. Primer
  2. Under coat
  3. Top Coat`
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8
Q

What is the role of the primer

A
  • Adheres to the substrate
  • Can protect metal surfaces from corrosion
  • Dries to matt finish to provide key for next layer of paint
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9
Q

What is the role of the undercoat

A
  • Provides a flat even surface

- generally dries to a matt finish to promote bond with final coat

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10
Q

What is the role of the top coat

A

-Provides colour, texture and protection

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11
Q

What are the different ways paint can achieve an impervious barrier

A
  1. By adhesion of the binder to the substrate which stabilises the substrate
  2. Formation of a barrier between the substrate and the deleterious influences (light, water gases….)
  3. By chemical action, some pigments react with aggressive agencies that might attack the substrate
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12
Q

For paint protection to be effective what must the substrate be

A
  • Firm
  • Clean
  • Doesn’t react chemically
    - Such as excessive alkalinity of new cement
    - Rapid oxidation of aluminium
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13
Q

2 types of opacity and examples

A
  1. Clear Coatings: varnishes and Stains

2. Pigmented: Oil based and thermoplastic

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14
Q

2 different types of bases for paints

A
  1. Solvent Based

2. Water Based

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15
Q

How should new timber be prepared for painting

A
  • Preservative treatment
  • Knotting
  • Primer
  • Stopping and Filling
  • One or two undercoats
  • One of two alkyd gloss or semi gloss top coats
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16
Q

How should old timber be prepared for painting

A
  • Selotape will pull away any loose flakes

- Substandard timber must be replaced and sanded down so no edge are left proud

17
Q

How should a cement based substrate be painted

A
  • Alkali resisting primer

- Finish with alkyd, emulsion, masonry or cement paint

18
Q

How should steel be prepared and painted

A
  • Initial protection must be carried out less than 4 hours after cleaning or the paint is adhering to an oxide coating and not steel
  • remove mill-scale by blast cleaning or pickling in acid
  • Surface needs to be above the ambient dew point to avoid condensation
19
Q

What is a sacrificial paint system

A

The paint corrodes in preference to the steel it is protecting
-Principles of electrolytic corrosion apply

20
Q

What is an intumescent paint

A
  • Used to provide fire resistance
  • On heating components in the paint give off non flammable gases (CO2 and ammonia)
  • Coating expands up to 100 fold, forming a rigid foam
21
Q

What is the importance of the time left between coats

A
  • If the minimum time between coats isn’t adhered to solvents in the upper coat may interfere with the drying of the lower coat
  • If the maximum time between coats isn’t adhered to he first coat has dried too hard and the subsequent coat will dry before the solvents have had a chance to penetrate the now hard surface
22
Q

Potential defects with coatings

A

-Adhesion failure
-Blistering
-Chalking
-Colour defects e.g. fading
-Cracking
Detachment of mill scale from steel
-Rust staining
-Organic growths
-Flaking

CVA106 (9 decks)

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