The Dos and Don’ts of Sealing the Deck
Avoid common mistakes when applying sealant that can leave your deck vulnerable to damage and hazards.
A backyard deck is the perfect platform for good times, but that wooden surface needs a proper sealant to protect it against the ravages of sun, rain, and temperature fluctuations. While you can hire a decking contractor to seal the surface, many homeowners opt to tackle the task—and save between about $550 and $1,260, according to HomeAdvisor. While sealing a wooden deck isn’t the toughest DIY project, there are definitely tricks and techniques that help ensure quality results. So consider these dos and don’ts for sealing a deck so you’ll get the job done right the first time.
DO wait 30 days before sealing a new deck.
If you’ve just put in a new deck, you’re no doubt itching to finish the job by sealing it. But preservatives in the wood often require about 30 days’ dwell time before the deck can soak up the sealant. After a 30-day period, pour some water on your deck. If it beads up, the wood is still too wet to seal, but if the water is absorbed, it’s ready to seal. Be sure to apply sealant as soon as the wood is ready; leaving the deck exposed any longer increases the likelihood of both ultraviolet (UV) and moisture damage.
DON’T confuse paint, stain, and sealant.
Sealant, stain, and paint can all be applied to a deck for different degrees of protection.
- Sealants are primarily used to protect against moisture damage. They contain waterproof or water repellant properties and have a thicker viscosity than stains. Unlike stains, sealants lack pigmentation and generally provide less UV protection than stains.
- Stains always include pigmentation, which adds color to the deck and helps protect against UV damage. Even the best deck stains generally offer only moderate moisture protection.
- Paint, be it latex or oil-based, can protect against both UV and moisture damage, but the best deck paint generally doesn’t hold up as long sealant or stain. Also, if there’s any lingering moisture in the wood during application, paint will be susceptible to bubbling and chipping.
Bottom line: A combined stain-and-sealant product offers durable, moisture- and UV-protection with the least drawbacks. In lieu of that, you can apply a simple stain to the deck and, after 48 hours, apply sealant for a similar level of protection.
DO repair, wash, and sand your deck before sealing.
Proper prep is key to successfully sealing a deck. Repair or replace any loose or broken boards, so that future breaks or cracks won’t create hazards. Then, wash the deck using a power-washer to scrub the surface clean. Allow to dry for 24 hours, then sand the surface with between a 60 to 150 grit sandpaper or sanding disk. Use a powered sanding tool to remove the top layer of wood, which could act as a barrier to the sealant.
On a previously stained deck, also be sure to sand the entire surface—areas where the sealant has worn away as well as those that still have moisture protection intact. This moisture protection would prevent new sealant from being absorbed, so sand evenly to ensure a clean, bare surface.
Finally, sweep or vacuum thoroughly. Even a brand new deck will need at least a brief washing and drying to banish any dirt and grime accumulated during the initial 30 drying period.
DON’T apply sealant to damp or frosty surfaces.
Applying sealant to a damp or frosty deck will lead, at best, to an uneven, splotchy seal that can’t effectively protect your deck. At worst, the sealant will bead up on the water and fail to be absorbed, creating a messy, dangerous slipping hazard. Always allow the surface to dry for at least 24 hours after a rainfall before sealing a deck.
DO use proper tools and technique for sealing a deck.
Deck sealant can be applied using a roller, a paint brush, or even a paint sprayer. You can work from a standing position with a pole or on your hands and knees (kneepads highly recommended). Work slowly enough to ensure that every inch of the deck gets an adequate amount of sealant.
Overly thick sealant is prone to peeling and chipping, so avoid oversaturating the surface by applying only one coat of sealant at a time. In most cases, all you’ll need is one coat, but should you wish to apply a second coat, wait at least 24 hours.
DON’T disregard temperature and time of day.
Plan to seal your deck when temperature and time of day are ideal. Aim for a pleasant, not-too-windy day between 50 and 90 degrees Fahrenheit. Get to work in the morning, as the hot sun of a summer afternoon can cause sealant to evaporate quickly, preventing adequate absorption.
DO apply a sealant-and-stain product once a year.
Consider this a general rule, depending on climate and the age of your deck. In sunnier regions, adhere strictly to a once-a-year schedule to protect the wood from powerful UV rays. Northern regions may get away with a two- or even three-year cycle; however, these regions are more susceptible to moisture damage, so be vigilant about sanding the deck before sealing to ensure that the sealant is able to soak into the wood to provide long term protection against melting snow and other moisture damage.
DON’T use the deck for 48 hours.
While sealant is normally dry to the touch within a few hours, for a proper seal that protects the wood, stay off your deck for two full days. To remind family members, put yellow caution tape across the access routes to the deck. After 48 hours, let the partying begin!