Understanding Wood Finishes, Paints, and Coatings
Wood Finishes, Paints, and Coatings
Softwood (carpentry) and hardwoods (furniture) exhibit different compression resistance. Softwood resists compression better in the direction of the grain. The resistance to anisotropy in compression and flex is 3pl/2ab2.
Paint Components
Paintings consist of varnish, binder, diluent solvent, plasticizer, and pigment. Solvents dissolve the binder. Organic solvents include turpentine or distilled turpentine resin. Mineral solvents include water or hydrocarbon derivatives. Plasticizers are not used in blotting. White spirit, alcohol, benzene, and methyl ethyl are also used.
Binders (Aglutinantes): form a dry film. Mineral binders include lime plaster. Seed oils, animal oils, or drying oils such as linseed oil, soy, and fish oil are used. Resins, both natural and artificial, from coniferous exudation of polymerized molecules, provide resistance to chemical and physical exposure. Silicone resins, fire retardant impermeabilizers, cellulosic resins, and animal and vegetable glues are also used.
Plasticizers improve flexibility and are non-evaporating liquids. They can be natural (oil) or artificial (glycerin). Drying agents accelerate the oxidation of fatty agents and include lead oxide, manganese, and cobalt.
Pigments provide opacity, body coloration, protection, hiding power, and stability. They are used in exterior applications.
Types of Paints and Coatings
- Water-based: Film-forming (cement, clay) emulsified in water. Tempera uses pigment and a film-forming cast.
- Oil-based: Uses drying oils with hydrocarbon solvents. Slow-drying gloss paint with a yellow fat film-forming resin oil sheen. Not resistant to alkalinity in interiors.
- Synthetic paints: Combine oils and resins for brightness and hardness. Chlorinated rubber base is resistant to alkaline media and waterproof.
- Epoxy: Film made of epoxy resin and catalyst-tar. Offers chemical resistance and is waterproof.
- Polyurethane: Glossy, hard, and resistant to chemicals. Sensitive to water and alcohol. Quick-drying nitrocellulose for wood and metal, polished on exterior surfaces.
Plaster Pastes and Coatings
Plaster pastes and coatings use synthetic resins with loads up to 2mm thick. Mineral reliefs use a thick film. Plastic paste with chopped grated gotele. Plastic coatings with mineral fillers are used in Tyrolean finishes with dragged grains. Marmolinas use transparent color binders with marble grains up to 2.5 mm. They provide waterproof plaster and retain lasting powder.
Specialty Paints
Anti-corrosion paints: Protect metals (rust Fe) by inhibiting the electrochemical process. Paint thickness is stagnating or products are sacrificial. Types include:
- Bitumen
- Fat (minium)
- Sacrificial with natural resins
- Peel-off varnish for temporary protection
- Fire retardant (intumescent) with a porous layer to stop flames
- Aluminum paste varnish for anti-oxidation and waterproofing, heat resistance, and decorative drawing.
Strippers
Strippers remove dried paint, tempera, and plastic coatings. They are applied with lime or with a brush or sandpaper. Oil-based coatings are removed with a solution of soda.
Paint Defects
Defects can arise from flames, paint or support incompatibilities, swelling/blisters from wet support, cracking from dimensional changes, paint peeling from different overlapping layers, poor adhesion, and areas with little oil. Comb thickness is used for control: Rp = Rtxfaxfr (Studies > theoretical).