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Related Readings:
Textured Walls
Textured Coatings
Products for Effective Surface Prep
Integral Colored Plaster
Getting Started in Venetian Plaster
Venetian Plaster: A Second Look
Elastomerics
Other articles in this issue:
Getting Started in Venetian Plaster
Exterior Acrylic Stains
Gilding
Respirators On the Job
Long-Range Planning
Contractor Profile: Jean Pierre Menguy
Paint Product News
Painting Tips

 

 
PaintPRO Archives  
Exterior Acrylic Paints

 

 

Wood Stain, Exterior Wood Stain,
Acrylic Stains

Semi-transparent stains offer a variety of tints that allow the grain and texture of wood to show through. Solid-color stains are heavily pigmented and cover the wood grain, but do not obscure its texture. Solid-color stains also provide more protection from the sun's UV rays.
By Ester Brody

Like many of the projects professional painters work on, selecting the right stain products for residential jobs requires “background” work before the first coat of primer is applied. For example, what kind of finish is the customer really looking for? Correctly applied, stain finishes will provide a true, flat finish that enhances the beauty of the wood surface. Semi-transparent stains offer a variety of tints that allow the grain and texture of wood to show through. In contrast, solid-color stains are heavily pigmented. These stains cover the wood grain, but do not obscure its texture. Solid-color stains also provide more protection from the sun’s UV rays.

Unlike stains, most house paints are formulated to provide a finish that differs from stain finishes in several ways. Many house paints labeled as “flat” still give off a low-luster sheen when dry. In addition, paints are manufactured to form a harder, more protective barrier than stains between the substrate and the environment. However, paints are more subject to peeling, since moisture can be trapped beneath the surface of the coating. Sample boards of stains and paints along with product literature from manufacturers will help demonstrate to customers some of the primary differences in appearance and performance between these two products.

Exterior Acrylic PaintsChoosing water-based or oil-based products
There are also considerations when selecting between oil-based and water-based products. According to Adam Churchill, manager of technical services and support for the Samuel Cabot Paint Company, technology advances in the development of water-based, acrylic products has had a positive effect on the industry. “In the past, oil-based products had the performance edge over many water-based products. But strict VOC regulations, and customer desire for top-performing products that also offer easy clean-up, spurred the development of new and improved water-based products.” Today, several paint manufacturers like Cabot offer water-based stains with acrylic binders that offer superior resistance to cracking, peeling and blistering due to the coating’s flexible, permeable finish. “Once dry, these finishes remain flexible enough so that moisture doesn’t become trapped beneath the surface causing the coating to peel,” says Churchill.

Another advantage offered by water-based stain with acrylics is their superior color retention. “We have found that our acrylic stain products do an exceptional job resisting fading,” says Gene Merrill, director of product development at Duron Paints & Wallcoverings. Many water-based stain products are also excellent at repelling water and resisting mildew thanks to additives that enhance these performance qualities. Water-based products can be used on new or weathered wood surfaces. The same products can also be used on cured masonry, stucco and primed metal. One of the primary advantages of water-based stains is the easy clean-up with soap and water. “Usually, this is a big plus for the do-it-yourself market, but we find that professionals like the quick clean-up as well,” says Churchill.

Exterior Acrylic PaintsOil-based stain products have their advantages too. Oil-based stains offer excellent penetration and dry to a harder finish than many water-based products. As a result, these stains are extremely durable. They also provide superior resistance to peeling, blistering and mildew formation, and repel water. Recommended substrates include wood siding, shingles, shakes and roofs. Oil-based stains are also ideal for rough-sawn surfaces. Brushes, rollers and spray equipment need to be cleaned with mineral spirits following their use.

Application differences can also be seen among oil-based and water-based stain products. For example, some stains are self-priming, while others require a separate primer to minimize tannin bleeding or to assure a properly prepared surface for coating. Some stains are recommended for vertical surfaces only, while others are used on horizontal surfaces like decks, docks and even outdoor furniture. Another application consideration is drying time. Oil-based stains have a longer “open” time, taking longer to dry than water-based stains. Because of this longer drying time, painters need to maintain a leading “wet edge,” staining a few boards or small areas at a time, according to technical data information from Duron. Back-brushing while the stain in still wet is also recommended if an oil-based stain is being spray-applied because this action forces the stain into the wood. Finally, the literature suggests that a second coat of oil-based product be applied within 10 to 15 minutes to avoid “lap” lines.

Substrate condition helps determine best product selection
Similar to any painting project, the condition of the substrate will help determine the type of stain product that is best for the job. New or weathered wood such as uncoated solid wood, plywood or pressure treated wood, are good candidates for either oil-based or water-based stains. Both types of stains also perform well on previously stained wood. For previously painted wood surfaces, solid-color, water-based stains are often recommended. In addition, oil-based and water-based stains are not recommended for wood surfaces that have been sealed with pigmented, clear gloss, or solid hide stains.

In all cases, the wood surface needs to be clean, smooth and dry to achieve optimum stain penetration and overall product performance. Old coatings and stains should be completely removed, exposing bare wood. Special products are also available to remove grade stamps, or to brighten wood that has darkened from the cleaning process. Other priming products are also useful in treating wood knots and areas with severe tannic bleed. Look to coating manufacturers for specific products that will minimize these and other problem areas.

Following additional guidelines from manufacturers such as not applying stain in direct sunlight, in humid weather, or in temperatures below 50zF, will help ensure a successful staining job. Churchill also cautions against the over-application of product which can result in a blotchy, shiny appearance. “When applying stain, more is not better,” Churchill says.

Exterior Acrylic PaintsStains for decks
Another aspect of staining involves coating decks and other horizontal surfaces. Unlike stains specifically recommended for siding, shingles and trim, stains for decks are formulated to sustain standing water and repeated foot traffic. However, some manufacturers make stain products that can be used for both vertical (i.e., siding and trim) and horizontal (decks and docks) surfaces.

Sealers are another type of finish that offer protection from the elements. Sealers are clear finishes that have no pigment. These coatings allow the natural color and grain of the wood to show through, but are not as good as semi-transparent and solid-color stains at blocking UV rays.

Finishes designed for decks offer a huge array of tints and colors. Once again, the manufacturer can provide the best direction on which products will be the best for the job. Manufacturers are also a great source for the latest trends in deck finishes. “We’re seeing a growing popularity of solid-color stains for deck finishes,” says Merrill. “More and more customers are interested in the deck color as a complement to other colors used on the house.”

Meeting customer expectations
Meeting customer expectations is always a top concern when undertaking any coating project. With stain products, however, many customers may not be as familiar with performance capabilities as they tend to be with paint. For example, no matter how superior the product, all exterior stains will fade with time due to exposure to the elements. By helping customers understand how products perform, they are more likely to recognize a job well done. Product literature from manufacturers is an excellent tool to share with customers and usually highlights the product benefits offered. Test panels using a sample of the wood that will be finished are also an invaluable tool that helps customers preview what the end product will look like.

If you are armed with the right products for the job, professional skills and customer information, every job can be a smooth one.

Q: What does acrylic do for paint?
A: Latex is the general term for a
milky-white mixture of water and microscopic particles of a plastic material (the binder). The latex dries to form a tough film that binds the pigment particles together, and provides film integrity and adhesion. In a water-based paint, the binder influences nearly all properties to some extent, including adhesion, color retention, scrub resistance, dirt resistance, mildew resistance, block resistance, and all aspects of durability. Acrylic is one type of plastic material used to make latex, and some other types are described in the next answer.

Q: What are the alternatives to acrylic products?
A: In latex primers and paints, the main alternatives to 100% acrylic latex are vinyl-acrylic (also called PVA), styrene acrylic, and ethylene-containing terpolymers.

Vinyl acrylics offer better initial economy than all-acrylics, and provide suitable performance for interior wall primers and paints. Appropriate all-acrylics offer maximum performance in resistance to alkaline cleaners, stain resistance and block resistance in premium flat, satin and semigloss interior paints. Most top-line exterior paints are based on all-acrylic binders because of superior adhesion under wet conditions, dirt and mildew resistance, alkali resistance, and general long-term durability.

Styrene-acrylics contain styrene to reduce cost and in some cases enhance gloss potential; are best suited for masonry sealers, direct-to-metal paints, and high gloss enamels; are relatively hard, and thus tend to crack in exterior wood applications, especially in flat paint formulations; tend to chalk and fade more than the other types, so are not used extensively for exterior finish coat products.

Ethylene containing terpolymers are relatively soft binders used mainly in interior paints, in low odor paints. They tend to collect dirt, and have limited utility in exterior applications.

Q: What does a 100% acrylic binder do for paint that other ingredients can’t?
A: All else being equal, 100% acrylic generally maximizes adhesion under wet conditions, water resistance, and alkali resistance, which is important when painting exterior masonry. To attain the best performance with a 100% acrylic product, other variables must be appropriate for the application, including ratio of binder to pigment, total solids content, and nature of other ingredients.

Q: Are higher levels of acrylic content in paint more advantageous for outside work or for the inside?
A: Outside work. Acrylics, as compared with vinyl-acrylics and styrene-acrylics, perform better in exterior applications. For interior paints, acrylics offer better wet-rub, food-stain resistance, block resistance, and wet-adhesion, than do vinyl acrylics, all else being equal. However, the differences are more significant in exterior applications.

Q: Do acrylics work well in primers?
A: Sometimes. Specialized acrylic binders are used for different types of latex primers, including interior and exterior stain-blocking primers, wood primers, and rust-inhibitive primers. They tend to provide better long-term crack resistance and rust inhibition than do oil-based primers. However, for difficult water-borne stains, oil-based and alcohol-based primers offer better stain blocking. Vinyl-acrylic latex binders are for the most part reserved for use in PVA wall primers.

Q: Does acrylic improve the flow and spread of a paint?
A: Not necessarily. The tendency for a paint to flow out after it is applied depends on many things, including application temperature, porosity of surface, humidity, how thickly the coating has been applied, and the nature of the brush or roller used, as well as on paint ingredients. Ingredient factors include solids content, levels of propylene glycol or ethylene glycol, and very importantly the nature of the thickener and the binder used. Thickeners and binders tend to interact and in turn influence degree of flow. Certain combinations of small-particle acrylic binders and synthetic thickeners are particularly effective for providing good flow. But acrylic content per se does not have a good or bad effect on flow.

Answers provided by the Paint Quality Institute, Philadelphia, PA. Visit the Paint Quality Institute Web site.

 
 
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