A texture undercoat is a white paint used for priming gypsum wallboard ceilings for subsequent application of a blown-on texture finish. These paints are generally latex-based and are high hiding due to an extremely high PVC (pigment volume concentration) and therefore have very porous dry films. Texture undercoats should not be used as primers for any surface that is to be painted as they have very little hold-out for regular paints.
An undercoater is similar to a primer sealer in that it functions as a intermediate coating that is used to prepare the substrate. Undercoaters generally have good hold-out or resistance to penetration by subsequent topcoats, with the notable exception of texture undercoat. This provides a base for a final finish that is uniform in color and gloss.
Varnishes are liquid, film-forming materials based on drying oils and resins. They’re applied in a thin layer and dry to a translucent film. There are several basic types of varnishes, including…
- Bituminous Varnish: a dark varnish based on bituminous ingredients. The varnish may be either of the oil or spirit type.
- Oil Varnish: based on resin and drying oil as film forming ingredients and is converted to a solid film primarily by chemical reactions.
- Spar Varnish: a varnish for exterior surfaces. The name originated from its use on the wooden spars of ships.
- Spirit Varnish: a varnish resin dissolved in alcohol that converts back to a solid film primarily by evaporation, e.g. manila, shellac.
Varnish stains are colored with a dye or pigments. These do not have the same power of penetration as true stains and leave a colored coating on the surface, which, in some cases, can appear muddy.
Many different types of water repellent paints are used in construction today. The simplest system is the monomeric silicone oil type that is flood coated onto unpainted masonry surfaces to reduce water intrusion. This type of coating must be renewed every 1 to 2 years to remain effective as the silicone oils are non-reactive and always mobile. Commercial water repellents generally contain a drying oil blended with a stearate (wax) and solvents; these can also be used on wood surfaces as the drying oil forms a film. Water repellent stains last the longest because their opacifying pigments reduce the effects of UV light (sunlight) degradation. Reactive water repellents for masonry and concrete surfaces can be simple materials like sodium silicate or complex specialty products like Isooctyl trialkoxysilane; these materials chemically react with the masonry surface to form a crystalline structure in the air voids that reduces water penetration. In addition to shielding exterior concrete and masonry surfaces from the elements, water repellents are often used to seal concrete construction such as bridge decks from water and salt intrusion, thus preventing corrosion of the steel rebar contained within.
Wrinkle paints provide a wrinkled surface finish effect when dry. They’re usually solvent-based and the paint chemist can manipulate the formula to achieve the desired degree of wrinkle.
|
