Paintings and Coatings Flashcards
What are the five constituents of paint
+explain briefly
- Vehicle-the liquid portion
- Binder-holds together all parts
- Solvent-to disperse the parts evenly
- Pigments-add colour
- Additives-variety of jobs
What are three types of additives
Driers
Plasticisers
Light stabilisers
Insecticides/fungicides
How do paints protect the surface underneath
By adhesion with the binder to the substrate
By formation of a barrier
By chemical action with pigments against aggressive agents
What are the three layers of a paint job
Primer
Undercoat
Top coat
What is the function of the primer
+how thick is it usually
Primer is 10-75 microns
and adheres to the substrate to allow a matte finish for next layer of paint
also sometimes protects metal surfaces
What is the function of the undercoat
+how thick is it usually
Undercoat is usually 20-150 microns
Masks any discolourations
while providing a flat layer for top coat
What is the function of the top coat
+how thick is it usually
Top coat is usually 20-30 microns
it provides colour, texture and protection
What is the preparation required for a new timber substrate
It must have preservative treatment
knot treatment
and sometimes two undercoats
What is the preparation required for an old timber substrate
Use sellotape to pull off loose flakes
and sand down/replace substandard timber
Use same method as new timber
What is the preparation required for a cement based substrate
Alkali resisting primer must be used
and must be finished using alkyd, emulsion or masonry paint
What is the preparation required for a gypsum plaster substrate
All plasterwork must be dried (about 30 days)
Most paints are compatible but if using alkyd an alkali primer is needed
What is the preparation required for a new steel substrate
Must be prepared before painting
by either blast cleaning or pickling in acid
paint must be carried out less than four hours after
What is the preparation required for a galvanised steel substrate
A protective zinc coating is added
calcium plum gage primer is needed
What are intumescent paints
+brief explanation on how they work
Paints used to provide fire resistance
On heating paint expands up to 100x to provide an insulating foam
What can happen if painting is done in cold conditions +specific temp
If painting is done under 4°C
the paint can not stick to the substrate and drip off
What is a potential problem with high winds for paints
Can cause rapid evaporation and dust
What is a potential problem with damp in paintings
Damp caught under the paint can cause blisters when the sun warms it
What is a potential problem with porous surfaces
Can cause the solvent to soak away
What is blistering
Blistering is when paint lifts from the surface
What is chalking/powdering
Chalking and powdering is when a fine powdery residue forms on the surface
due to damage from UV exposure or poor paint quality
What is mill scale and why is it a problem
Millscale is a thin layer of iron oxides
that form on steel and can fall off and remove paint film with it
