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How To Paint - Primer Part 2 - The Primer on Primers
Undercoats are considered primers. Although many people consider primers as a type of paint, there are distinguishing factors that make primers - well, primers. First, they are usually thinner than paint (or top coat) and they are relatively flat for better intercoat adhesion. Second, they contain much less pigment than do top coats.
It is not unusual to find some topcoat manufacturers suggesting that their product-line matches certain primers. It is important to pay close attention to this because one primer formula may not be compatible with a different manufacturer's topcoat, resulting in saponification and paint failure. Be aware of label suggestions and requirements.
The basic features of primers are:
- Improving the Appearance and Longevity of a paint job especially for surfaces that have never been painted or are being repainted after stripping. The primer creates a bond between the surface and topcoat.
- Prevents absorption and uneven hide of porous or recently repaired surfaces.
- Reconditions Existing Coatings: If a previously painted surface is chalky, primers will create a workable surface.
- Provides Hide: from underlying stains.
- Fills Surface Flaws such as pores and indentations creating a smoother surface.
- Resists Moisture: When the substrate is wet, paint will not bond.
- Inhibits Rust: Keeps oxygen and/or metal away from the substrate.
- Resists Chemicals: Water based primers can be used on substrate exposed to mild chemicals, while for commercial and industrial settings an oil based primer might be more suitable .
Latex vs. Oil/Alkyd Primers
Alkyd Based Primers:
Available for over 20 years, these dominated the primer market for a long time. Just about any topcoat will adhere to an alkyd primer. The really big plus for such a quality primer is its ability to adhere well to glossy, hard, greasy and oily surfaces. A lot of painters prefer alkyd primers for stucco and they are particularly well-suited for raw wood since they won't raise the grain like a latex primer. Some drawbacks include a tendency to raise the nap in the paper of wallboard, and it will not adhere as well to plaster or alkaline surfaces.
Alkyd primers are exceptional for blocking water soluble stains, and since most stains that painters encounter, are water soluble, it is a good choice to use.
Water Borne Primers:
A key advantage to this family of primers is that they will adhere to almost anything - including glossy paint if it is sanded first. With many newer water borne resins, the adhesion characteristics are much enhanced. Some painters feel that their performance is comparable to solvent based primers . These primers can be used extensively on exteriors that are subject to weathering and interiors where odor should be kept to a minimum. The newer technology latex products are good at concealing water stains and smoke damage and almost any paint will adhere to them. Water borne primers perform better on wallboard, galvanized metal and masonry. They will resist many chemicals better than solvent based primers, but not heavy chemicals such as bleach. Among the most desirable attributes of water based primers are their low odor and ease of application, along with low cleanup costs and reduced volume of pollution forming VOC. emissions.
Shellac: The Granddaddy of Primers
White Pigmented Shellac is derived from the 100% natural and nontoxic resinous secretion of the lac insect. Despite the older technology its consistently high level of performance continues to earn the loyalty of pro painters and amateurs alike. Many of shellac's applications have never been equaled by synthetic chemistry. For instance, its natural volatility causes its solvents to evaporate quickly and completely resulting in it drying faster than other primer-sealers. Another advantage over alkyds and acrylics is that it will dry and cure promptly even in exterior cold temperature applications.
Pigmented shellac offers relatively easy cleanup; Brushes can be washed with a solution of household ammonia and water. Besides being inexpensive it is also non toxic and environmentally safe.
Other Primers and Sealers
Concrete Block Filler
Designed to fill and seal porous concrete and cinder block construction without obliterating the natural texture. Block filler will give a uniform texture even where stucco has been patched or the surface is uneven. A prime use of Block Filler is to fill voids in exterior masomy and develop an effective barrier against moisture and water absorption. Concrete block filler is not recommended for use on old, chalky or extremely glossy surfaces and will not control expansion cracks.
This primer is designed to provide a smooth, non-porous base for flat wall paint or enamels over any interior surface. Recommended as a first coat over unpainted wood or masonite, it can be used on walls, ceilings, trim, doors, cabinets, paneling or wood floors. It dries overnight to a hard finish and can be applied with brush roller or spray. Cleanup requires paint thinner.
Exterior Wood Primers
These primers have controlled penetration, sealing and binding qualities. They may be used over smooth wood siding, masonite, high and low density boards, shakes and rough-sawn lumber, wood porch floors and decks, sash, trim, doors or any other exterior wood surface. It is ideal for resealing badly weathered, previously painted surfaces. Special primers are available which resist mildew and some are formulated specifically for use with latex house paint. A recent development is a water-thinned acrylic exterior wood primer that you can prime with and finish in one day.
Latex Metal Primer
An acrylic latex protective coating formulated to inhibit rust and to coat weathered metal surfaces. This primer is particularly suited for galvanized surfaces.
This is a rust inhibitive primer designed for mildly rusting iron and steel. May be used for interior and exterior ferrous surfaces such as steel sash and frames, metal doors, siding, piping, decking, ornamental metalwork, structural steel, etc.
A very hard drying, solvent type, first coat sealer. It seals the porous surface and prevents suction of surfaces such as plaster, wallboard, cement, stucco, etc. This primer promotes an excellent finish with only one finish coat of enamel or wall paint. Mainly for use on interior block, brick, concrete, plaster, thin wall, hard wall, spilt face block and gypsum wall board. It is recommended as a base coat for deep tones because of its excellent sealing properties.
Pigmented Surface Conditioner
A deep penetrating, pigmented primer designed to bond and harden old, porous type cement paint and heavily chalking oil base paints, so they can be repainted without sandblasting. This conditioner is alkali resistant and, when properly used, will allow you to paint successfully over surfaces that are normally hard to paint. Designed for previously painted surfaces it is also recommended as a prime coat for all color coat stucco on the seashore.
Siliconized Masonry Water Repellent
A clear, non-staining water repellent for masonry . It does not fill voids but keeps masonry dry. Recommended for water-repellent treatment of close grained masonry such as stucco, concrete or brick and for properly filled concrete or pumice block .
Like its name indicates it is a fast drying, non-lifting primer for use on interior or exterior surfaces. It can be used as an intermediate coat over existing paint to prevent lacquer, epoxy or vinyls from lifting the old finish. It adheres easily to hard glossy surfaces and can be recoated quickly. This primer is recommended for interior or exterior use over old paint or slick, hard surfaces. May also be used as a primer on bare metal and is ideal for marine use. Not recommended for exterior wood, however.
Vinyl Interior Pigmented Sealer
An interior, water-based wall sealer for dry wall, plaster and masonry. Has outstanding opacity and sealing properties. Recommended for sealing new or previously painted porous interior surfaces such as thin wall, hard wall, gypsum wall board, cement-asbestos board, plaster, concrete, block, brick, etc. This sealer is not to be used when the surface temperature is below 50°F.
Zinc Chromate Primer
An interior-exterior synthetic primer with excellent rust inhibitive characteristics. Specifically formulated for use on aluminum it can also be used on all exterior or interior iron and steel.
Once you are properly prepped you're ready to get to it..... but hold up there painting cowboy. What kind of coating should you use, especially if your valued project has some special characteristics? Our next section will explain Specialty Coatings and what they are used for.