Wk 10 Paints and coatings

What is paint used for?

• to prevent deterioration of metals/timber etc

• can be expensive

• can be decorative

What are the constituents of paint?

• vehicle (liquid portion)

• binder (holds pigments together)

• solvent/thinner

• pigments

• additives (include driers, plasticisers, insecticides and fungicides)

How does paint protect materials?

• adhesion of the binder to the substrate - stabilises the substrate

• forms a barrier between substrate and deleterious influences

• by chemical action - some pigments react with aggressive agents that might attack the substrate

• creates an impervious barrier against water

What are the components of typical pain systems for domestic construction?

• primers (adheres to substrate, dries matte helps next layer stick, makes sure the wood doesn’t absorb too much binder)

• undercoat (masks discolorations on the surface, makes surface flat, helps next layer stick)

• top coat (provides looks, aesthetics) (colour texture protection)

How would you prepare new timber?

• preservatives

• primer

• one or two undercoats

How would you prepare old timber?

• remove loose flakes

• if substandard, timber must be replaced

How do we prepare cement based substrates?

• alkali resisting primer/base coat

• finish with cement/masonry paint

How do you prepare plasterwork?

• needs to be fully dry before paint

• most paints can be used

• for a porous surface, thinned emulsion coat can be used

How do you prepare new steel?

• must be painted within four hours after cleaning - so paint sticks to material not the oxide - can flake off

• remove the millscale by blast cleaning/pickling in acid

• no condensation (must be above the ambient dew point)

How do you prepare galvanised steel?

• applying protective zinc coating iron to prevent rusting

• primer

• undercoat

• topcoat

What are intumescent paints?

• used to provide fire resistance

• when in fire, the components in the paint five off nonflammable gases

• the coating can expand and form a rigid foam

• usually water sensitive - not suited for external use

How can paint propose a risk to health?

• lead no longer used as an additive (used in old paints/primers)

• some solvents are toxic (wear a mask, well ventilated area)

• some paints can cause dermatitis

• some can pass into the body through skin

What can potential problems be caused when applying paint?

• temperature below 4 C can prevent paint from sticking to substrate

• below 10 C may not cure / airdry for a long time

• high temps can also be a problem

• wind - cause evaporation/dust

• dampness can cause blisters beneath the paint film when sun warms it

• porous surfaces - can cause solvents to soak away and leave a weakly bound material

• time between coats (maximum time is also important)