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Oil or latex? That is the question

Should you use oil-based or latex exterior paint? Should you use an oil-based primer or a latex primer? These are questions that often are asked. Unfortunately, the answers sometimes given can be confusing. In general, a good acrylic latex finish coat will always out-perform an oil-based finish coat in terms of longevity and color retention. In general, a good acrylic primer will provide a better base for finish coats than an oil primer.   Latex coatings form a film on the top of the surface. There is little penetration into the wood fibers because the latex molecules are too large and they don't go down into the wood fibers even if the paint is reduced way down in viscosity. However, latex does adhere very tightly to firm wood surfaces. Oil-based finishes do penetrate into the wood fibers to some degree. The molecules are smaller and some work their way into the wood.   For exterior exposure applications, paints containing 100% acrylic resins are recommended. They have better performance than paints formulated with only vinyl acrylic resin   For new unpainted wood, the best choice is almost always acrylic latex primer and acrylic finish coat. The only times oil-based products would be used is if the wood has weathered and the top layer of the wood has become soft and punky. You can tell if this is the case if you carefully scrap your fingernail across the surface of the wood and there are several wood fibers caught under your fingernail. CAUTION! At one time wood splinters were shoved under prisoner's fingernails as a form of torture. If you get a splinter under your fingernail you will quickly learn why this method of torture was so effective. If this caution disturbs you, you can also tell if the wood has started to degrade by firmly applying a piece of transparent Scotch tape to the wood surface and pulling it off. If there are several wood fibers on the tape, the sun's UV rays have already done their dirty work.   If these tests indicate the wood is sound, use acrylic latex primer and acrylic latex finish coat. If the tests indicate the wood has degraded, the preferred method is to remove the dead punky fibers by scraping or sanding. Test again to see if any fibers come loose. If there are no fibers coming off, use an acrylic primer and acrylic topcoat. If you don't remove the loose fibers, use an oil-based primer followed by an acrylic finish coat.   Oil-based finish stains do allow more of the wood texture to show through than does latex stains, so if you want to maximize the appearance of the wood texture, use an oil-based stain.   For previously painted wood, a primer is not necessary to be used other than spot priming of repaired areas. The usual preparation work, i.e. scrapping loose paint, filling nail holes, sanding, caulking, spot-priming, etc. is required for both acrylic latex and oil-based finish coats. If the old paint is in sound condition and the wood is sound acrylic latex paint should be used. If the wood is in very poor condition, pitted, cracked and soft, oil-based primer followed by oil-based finish coat is the best choice. In this case, it is hoped that the deeper penetration of the oil-based products will help to hold things together. We would not expect the applicator to warranty this type of job!   For vinyl, aluminum and steel siding, acrylic finish coat should be used. No primer is necessary. It is important that chalk be removed before painting. There is no reason to ever use oil-based paint on these substrates.   For unpainted galvanized metal, use a 100% acrylic latex primer followed by an acrylic topcoat. Do not use an oil-based primer on bare galvanized metal. The zinc in the galvanized metal reacts with the oil resin causing paint failure.   For masonry surfaces, use acrylic finish coats and acrylic primers if required. Most acrylic finish coats designed for masonry do not require primers. Oil-based finishes should not be used on masonry because a chemical reaction occurs between the masonry and the alkyd resins found in oil-based paints. This reaction degrades the oil-based finish.   Graham Exterior Products 142-Series Aqua Borne Ceramic Lo-Sheen House & Trim 152-Series Aqua Borne Ceramic Acrylic Soft Gloss House Paint 932-Series Aqua Borne Ceramic Acrylic Solid Hide Stain & Flat House Paint 100-00 Aqua Borne Ceramic Universal Primer & Stain Blocker 685- Aqua Borne Ceramic Lite Masonry & Waterproofing Basement Paint 895-Aqua Borne Ceramic Masonry & Basement Paint   112-Series Elite Acrylic Eggshell 962-Series At Home with Nature Rustic Oil Stain 953-Series At Home with Nature Siding & Deck Stain 225-Series Pro Finish Latex Flat 162-00 Elite Super Hide Gloss Oil House Paint 165-00 Elite Super Hide Satin Oil House Paint 380-00 Acryplex#1 Universal Sealer-Latex 202-00 Elite Oil Primer 210-65 Aqua Borne interior/exterior Latex Primer 177-75 Bright Red Oil Barn Paint 247-75 Bright Red Latex Barn Paint

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