YONKERS, NY — Consumer Reports’ tests of more than 40 exterior paints and stains for the June issue reveal that newly reformulated finishes—often changed by manufacturers to meet government rules limiting volatile organic compounds—might not wear the same as earlier versions.

Manufacturers admit it’s a challenge to reduce pollutants without compromising performance. CR’s latest fully tested paints did not fend off dirt and other weathering effects for as long as some past products.

Because reformulated finishes might not wear the same as earlier versions, CR removed all such previously tested products from the ratings. That’s why a few familiar brands, including some of last year’s top scorers, are not included. But there are several new picks from Valspar and other brands with durability and value.

Full tests and ratings of exterior paints and stains appear in the June issue of Consumer Reports, on sale May 6. The report is also available to subscribers at www.ConsumerReports.org.

The ratings include results for major brands after a year or two of accelerated outdoor testing, equal to about three to six years on a house. Full test results represent 3 years of testing, or about 9 years on a house. Some initially promising finishes look far less impressive after  the equivalent of roughly nine years. The tests also showed that some lesser-known paints looked better than some heavy hitters and some stains needed to be reapplied after the equivalent of only three years.

Two smaller brands scored the highest: California 2010 (flat), $38 per gallon, topped CR’s tests for paints, and Kelly-Moore Acry-Shield (flat), a close second, $32, was also designated a CR Quick Pick. Some versions of Kilz, sold at Wal-Mart, had trouble keeping clean after the equivalent of six years, while several from Ace, Behr, (Home Depot), and Benjamin Moore needed cleaning after the equivalent of only three years.

Olympic Premium 596xx (opaque latex) $21 per gallon, was tops among stains. CR’s testers concluded that opaque stains as a group save time and money because they outlast semitransparent stains. But even the best opaque stain won’t last as long as most paints.

For glossier paint, Valspar Ultra Premium Satin (low luster), $24 per gallon, and Valspar Ultra Premium Semi-gloss, $25, were CR Quick Picks. Among stains, Behr Plus 10 (alkyd/water cleanup), $20, and Thompson’s Water Seal Deck & House (latex), $18, were also named CR Quick Picks.

Most homeowners refinish their siding every six to 10 years. To find out which paints and stains would probably last that long on houses, CR spread finishes over untreated yellow-pine boards, which tend to swell and crack, creating an especially tough test. Testers faced the boards south at a 45-degree angle on the roof of CR’s Yonkers, N.Y. headquarters to intensify the effects of sun and the elements. Each year of outdoor testing equals roughly three years on a home. Testers checked for dirt buildup, color change, mildew, and cracking.

“Some of CR’s previous top performers aren’t doing so well in our tests so far,” said Bob Markovich, Home and Yard Editor, Consumer Reports. “That’s why it’s really important not to assume that a paint or stain will have the same results as last time without checking CR’s ratings.”

Painting Tips

This year, consumers could spend several dollars more per gallon for exterior paint and stain thanks in part to the pricier petroleum that goes into them. That might tempt homeowners to pick a lesser-grade coating. But CR’s tests show that penny-pinching could cost consumers more over time. Here are some tips keep in mind when getting ready to paint:

• Match the paint to locale. Homeowners in cool, moist, or shady climates should look for mildew resistance. Dirt resistance is more critical in urban and industrial areas, and resistance to color change is more important in sunny locations and climates.
• Know what your pro is using. A professional painter’s choice might not be a top pick in CR’s tests. Make sure the written contract clearly states the brand, line, and cost of the pain or stain used.
• Look for hidden savings. Refinishing a 2,000-square-foot house will require roughly 10 gallons of stain and up to 20 gallons of paint. Consumers can often cut paint costs by buying two five-gallon containers instead of 10 one-gallon cans.
• Invest in proper paint work. Make sure all loose or peeling paint is sanded or scraped  off the surface. Remove old, cracked caulking and fill cracks around windows, doors, and  trim with acrylic caulk.
• Check the forecast. Many paints applied in cold weather might not dry properly,  resulting in poor adhesion. Also, rain can wash paint right off the siding if it hasn’t dried.  Temperatures between 60 and 85 degrees with no wind are ideal.