Drying of paints

1. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
PowerPoint
Drying of paints
presentation
Unit 216: Applying paint systems by brush and roller to
complex areas

2. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Learning outcome
• Understand the drying processes and stages of paint coatings.

3. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Drying of paints
Coatings dry by various methods:
• Evaporation
• Oxidation
• Polymerisation
• Coalescence

4. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Evaporation
• The solvent or thinner is dispersed into the air leaving the solid
constituents to form a dry paint film.
• Coatings that dry by this method can be reactivated by the addition of
solvent, returning them to a liquid. These are known as reversible
coatings.
• Two examples of this type of coating are shellac and bitumen.

5. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Oxidisation
• Oxidisation is process of drying whereby the air combines
chemically with the drying oils and resins present in the paint. This
has the effect of holding the pigment in suspension.
• Oxygen is drawn into the paint film by drying the oils and is in turn
passed on to the resins (oxidising the coating internally).
• Once set the paint cannot be reversed – the paint goes through a
chemical change.

6. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Polymerisation
• A drying process of some resins used in paints and adhesives,
which will not dry normally by absorbing air from the atmosphere or
by evaporation of solvents.
• The resins have to be mixed with hardeners. When this occurs a
chemical reaction takes place and particles of resin join together to
make larger particles. They eventually become hard and dry (non-
reversible coatings).

7. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Coalescence
• A drying process whereby the resin
content of the paint or adhesive is
separated by globules of water.
• When the solvent evaporates (water)
the resin joins together to form a solid
film.
• The gaps left by the water are not fully
used up by the resin and the result is a
honeycomb effect.
• This is the characteristic of PVA or
acrylic emulsion paints.

8. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Questions
1. List the three main methods by which paint dries.
2. How do emulsion paints dry?
3. Explain oxidisation.
Image reproductions courtesy of Decorating Warehouse and Axminster.

9. © 2013 City and Guilds of London Institute. All rights reserved.
Level 2 Diploma in Painting and Decorating
Any questions?