Deck Sealants are Worth the Trouble

If you are wondering why you can’t use just any finish on your deck, think about the abuse decking must handle, in­cluding pounding rain, snow, and ice, abrasion from traffic and furniture, and often many hours of direct sun, day after day. To make matters worse, the joints between the many parts of a deck retain moisture long after the rain stops, making the wood vulnerable to rot, mildew, and wood-munching insects. To combat this barrage, deck-fin­ish manufacturers offer a variety of formulations that in­clude sealers, preservatives, UV-light inhibitors, pigments, and resins. Some are oil based and penetrating. Some are acrylic and film forming. Others are a mix. Here is a list of the most popular finishing options for a new deck:

Clear sealers, or water-repellent preservatives, are the most popular choice for new decks. They help protect wood from moisture, thereby saving it from repeated cycles of soaking up water and then drying out. Unprotected, wood will crack, warp, cup and splinter. Sealers must be reapplied regularly to remain effective then; the wood will weather to gray. Water- repellent preservatives contain a fungicide to fight mildew.

Toners, or transparent stains, offer more than clear sealers. They deepen and enhance the wood, and the grain remains visible. You can use finishes on pressure-treated wood to approximate the look of more expensive woods. The best products in this category penetrate the wood surface, protect it from UV light and mildew, and leave a substantial top layer to resist moisture. They are relatively expensive finishes but will retain the original color of most woods strictly according to the manufacturer’s directions.  Note: Exotic hardwoods like Ipe or mahogany are dense with natural oils and don’t absorb penetrating stains as well as softer woods. Allow them to weather to a teak-like gray or treat them with a hardwood-specific finish according to the manufacturer’s recommendations to maintain the original wood color.

Semitransparent stains generally have more pigment than transparent stains and do a better job of hiding imperfections and unattractive grain patterns. Alkyd- and oil-based versions excel because they penetrate the wood better than acrylic formulations. All are available in a wide variety of wood tones and colors.

Solid stains are more heavily pigmented than semitrans­parent stains. (Think thinned paint.) They offer superior protection against UV rays and hide the color and grain of the wood. They, too, come in a wide variety of colors. Oil-based products usually last longer, but water-based formu­las are easier to clean. Expect wear patterns to show in heavily-trafficked areas.

Deck and porch paints, unlike many stains, are film-forming products. This makes for superior UV and mois­ture protection, and is great for camouflaging lesser grades of lumber—but paint may blister and peel, and will even­tually show wear in high-traffic areas. Use paint if you want a bright gloss or semi gloss finish to match or complement paint on your house exterior. Acrylic- and alkyd-based paints are available and should be applied over an oil-based primer. Mix the paint with clean sand to improve slip re­sistance if desired. Keep painted decks swept free of dirt (it wears finishes away faster), or place outdoor carpets along traffic paths to prevent wear. Sand and recoat as necessary.

Preservatives prevent fungal growth, rot, and decay— and some also protect against wood-boring insects. They are recommended for treating untreated wood as well as the site-cut ends of pressure-treated lumber. Preservatives alone are not finishes. They may, however, be sold in com­bination with sealers to provide moisture protection as well, making them a one-step finish. Some preservatives can be used prior to applying paint for added protection against rot and decay.

Apply one thin coat of finish to penetrate and dry completely. Thick layers of finish don’t penetrate nor dry completely. The wood should be dry before applying finish. Sprinkle a little water on the deck. If it soaks in immediately, the wood is dry enough for finish application. New pressure-treated lumber must dry out completely before finish is applied. Check with the lumber supplier for the proper amount of drying time.

Make sure whatever finish you apply is rated for outdoor use and for a deck surface. Follow manufacturer’s application instructions for best results. And don’t spray or paint yourself into a corner.

Use a deck brightener to clean a deck before applying new finish (page 184). A brightener removes dirt, mildew, and the top layer of sun-faded wood fibers to restore the natural color of cedar and redwood.

Reapply finish to decks approximately once a year. Harsh climates and heavy deck usage may require reapplication twice a year.

Sealant types and Their Uses

Sealants refer to a wide variety of materials that are used to close the gaps between substrates, or various building materials.  Sealants are used to prevent air, gas, noise, smoke, liquid, or dust from penetrating small openings that cannot otherwise be closed.  Sealants begin as a viscous liquid, when applied, then dry into a solid.  Sealants of some sort are used in every level of civilization, from tarring the roof of a hut to weatherproofing a modern home with silicone caulk to specialty soundproofing.

In the past few decades, the sealant industry has globalized with the rest of the world market.  In fact, 60% of total global merchant demand of sealants comes from three major players.  Asia and India represent the highest growth market in recent years, due primarily to the rise of textile manufacture, electronics assembly, and woodworking.  Enduring woodwork would be impossible without the right sealants.

Sealant production has also responded to environmental concerns, with technological breakthroughs that have made sealants more effective and environmentally friendly.  Earlier generations of sealants commonly contained VOCs, or “volatile organic compounds.”  Advances in technology have produced Low-VOC and No-VOC sealants.  These new generation sealants are safer for the environment.  What’s more, they are applicable to a wider range of materials and conditions.

There are literally dozens of types of sealants, based on their chemical makeup and their various uses.  From dental sealants, to engine sealants, to household epoxy.  They are even used in the nanotechnology industry.  The most commonly recognized sealants are household sealants.  For example, the caulk used to seal a bathtub, window sill, or kitchen sink.

Sealants have three basic functions

1. A sealant fills a gap between two or more substrates.

2. Sealants form a barrier through the physical properties of the sealant itself and by adhesion to the substrate.

3. It maintains sealing properties for the expected lifetime, service conditions and environments.

Sealants are commonly grouped with adhesives, though they are different substances with distinct uses.  Adhesives are sometimes reformulated into sealants.  An adhesive is used to join to components together, like the panels of a cardboard box. While a sealant, though often sticky, is used to close gaps and openings where unwanted air and particles can pass through.  Adhesives are often stronger than sealants, but less flexible.  Sometimes the functions of sealants and adhesives overlap. Sealants do need to stick to what they are sealing, but that is not as important as the seal itself.

Sealants, though usually weaker than adhesives, have unique properties. Sealants, as opposed to simple adhesives, are particularly effective in keeping moisture in or out of the components they seal.  They provide soundproofing and thermal insulation.  Some sealants are quite effective as fire barriers.  Other sealants can have electrical insulating properties.  They are also used for finish work, like smoothing or filleting.

Sealants are a godsend in the field of home weatherproofing, and renovating kitchens and bathrooms.  The modern home would be impossible without the insulating properties of sealants.  This winter, try tracking down some of the drafts in your home – cracks and gaps around windows, under sinks, tubs and plumbing, or around electrical fixtures.  These are all places where household sealants, like silicone caulk and epoxy can make your home more comfortable and fuel-efficient.

Be sure to weatherize your home this season.  When doing so, don’t underestimate the utility and effectiveness of sealants.  Drafts can be eliminated and bills lowered all for the price of a few tubes of the right caulk.  There are numerous sealants on the market, each specialized for a different use.  Find out which ones are best for your needs.  Contact a local contractor that will answer your questions.

Some of the information in this report was gathered from The Third Edition of the Global Adhesive and Sealant Study: 2003-2006.  If you have questions about sealants and their uses, you may also contact the author of this article, Matt Millsap, a Tennessee based building and construction specialist.