How to Seal a Deck

  • November 26, 2019
  • / By Dale Keese
Wood Planks

A wooden deck not only adds beauty to your home, but it is also a great place where you can relax with your family and friends. Your wooden deck is exposed to harsh weather conditions such as direct sunlight, rain, humidity, freezing temperatures, the summer heat, insects and pests. And, if left untreated, the deck can deteriorate pretty quickly. Even decks made from decay-resistant or pressure-treated lumber will deteriorate when exposed to these destructive influences.

Wood Planks

Wooden decks need regular, attentive maintenance to preserve their good looks. And, the best solution to preserve your deck is to treat it with a preservative product that repels water, blocks the ultraviolet rays, inhibits mold and mildew and resists decay. Refinishing your wooden deck and sealing it regularly will help to keep it splinter-free, looking beautiful and usable for several years.

Exposure to extreme cold and heat has a detrimental effect on your wooden deck’s surface. You can preserve and protect your deck by sealing and staining it. Sealing offers specific advantages. A deck sealer is essentially a transparent coat that penetrates the wood and forms a film on its surface while preserving the natural finish of the wood.

Lookout Point

When the sealer penetrates the wood, it creates a protective layer, which minimizes the infiltration of water and also helps to keep out the moisture. The preventative finish of a sealer is vital in helping to reduce wood rot and fungal growth, which can reduce the lifespan of the deck. The sealer also reduces the effect of damage caused by water and protects the wood against the harsh UV rays of the sun, which causes the wood’s natural oils to dry up, resulting in fading, splitting and cracking of the wood.

Not only does the sealer protect your wooden deck, but it also improves the overall look and gives it a better finish. Also, if sealed properly, the wooden deck will be more durable and long-lasting. The process of sealing your wooden deck is quite easy and you can do it as a simple DIY project. However, before we get on to discussing how to seal your wooden deck, let’s look at other aspects of the deck.

Choosing the Right Deck Wood

Choosing the right material for your deck can impact your budget, as well as the final outcome. Nowadays, plastic and aluminum are becoming quite popular as materials for decks; nevertheless, wood remains to be a firm favorite. Let’s take a look at some of the common types of wood that are used for decks and the advantages and limitations of each.

Composite Wood

While composite wood has been in existence for a while, it is only now becoming popular. Composite wood consists of a blend of wood and plastic particles and while it can be either solid or hollow in construction, it resembles regular wood. Composite wood is more expensive compared to regular wood, but it is also more durable and requires less maintenance. 

The cost of composite wood decks usually ranges from $7 to $14. You can also buy composite material that is made from recycled plastic to make your deck more environmentally friendly.

Pile of Wood


Composite wood needs less maintenance compared to natural wood and is more resistant to pests like termites and you also don’t have to worry about knots, cracking, splinters, refinishing and sanding. Also, composite wood is available in a wide range of colors.


Often, composite wood behaves just like natural wood, which means that it is also susceptible to mold, heat expansion, fading and scratching. You can opt for UV-treated or scratch-resistant boards; however, this increases the overall cost. Also, it is not possible to paint the composite wood that has faded, without it chipping off. Hollow composite boards do not expand as much; however, they can warp in one place and may also retain water, resulting in mold growth and decomposition.

Pressure-Treated Wood

In recent years, pressure-treated wood has become the cheapest and most popular type of wood for wooden decks. The treatment of the wood is being done with safe chemicals in order to reduce its toxicity; however, the wood still has a greenish tint, which is characteristic of pressure-treated wood.

Natural Patterns


The biggest plus of using pressure-treated wood is its low cost. The wood is very easy to cut and can be held with screws and nails. The wood used is usually southern yellow pine, which is both available in abundance and is also very attractive. The treatment process of the wood makes it highly resistant to rot, fungi, and pests like termites.


Although pressure-treated wood is resistant to several wood-related issues, it needs the most maintenance, which can increase the cost of the deck in the long run. Also, the wood is prone to warping, splitting and cracking. And, to prevent damage, every few years, the wood must be reapplied with preservatives or a sealer/ stain.


If you don’t mind spending more on your deck, then an ideal material may be hardwood. Usually, hardwoods are tropical and may have to be imported. However, hardwood decks are easier to maintain, which can offset the higher material cost.

Mahogany Tree Forest


Hardwoods are not only rich in terms of the grain patterns, but they also are highly durable. They are resistant to infestations and rot, naturally. There are several options of hardwoods available in the market; however, ipe, teak, mahogany are the most popular types.


Using hardwoods has a few limitations. Firstly, hardwoods are quite expensive and the imported varieties are even more so. Secondly, the wood is very dense, which makes it quite difficult to drive in nails and screws. While drilling a pilot hole is helpful, nevertheless, the job is quite time-consuming. 

And finally, hardwoods tend to fade over time and are resistant to most types of stains and sealers. A new hardwood deck usually requires around 3 months, so that all the excess oils are eliminated before you can prime it for finishing and sealing.


Woods like redwood and cedar are softwood options, which are medium cost and quite attractive options for decks. These softwoods are naturally resistant to problems commonly associated with wood and do not require any chemical treatment. However, when you buy softwood, you must determine whether it is sapwood, sapwood-streaked or heartwood.

Each type of wood has its qualities that affect the price and also the resilience of the deck in the long run.

Cut Heartwood
  • Heartwood: This is from the tree’s center and has a higher level of oils and tannins that make it resistant to infestation and rot. The heartwood is denser and there are lesser chances of defects.
  • Sapwood: This comprises of the outer layers of the tree that is younger. It is cheaper compared to heartwood and is softer and less resistant to deterioration.
  • Sapwood-Streaked Wood: This is in between heartwood and sapwood and is most commonly used in the construction of decks because it offers the best balance of quality and price.


Cedar is among the best woods for construction and is popular for its pleasant aroma and beauty. You can get variants of cedar such as red cedar. Redwood is also a very popular choice. Heartwood is highly resistant to rot, infestation and decay, which reduces the need for maintenance as compared to pressure-treated wood, although even softwoods require some amount of maintenance.


Softwood is expensive compared to pressure-treated wood and is around three times more in terms of the cost. Also, over time, the color of the softwood fades to a grayish color and to maintain the original color, you will need to apply a stain regularly. And, the softwood must be treated with a preservative or new finish once in 3-4 years.

Determining the Type of Wood on Your Deck

Decks are usually built using cheap, durable and locally-sourced wood. Identifying and determining the kind of wood that has been used in your deck can help you decide how to treat the wood. For instance, some types of wood when painted will show the grain even through the paint. Other kinds of wood may work better with a stain and so, it is important to identify the wood before you decide on the treatment.

Axe on Block
  • Examine the color of the wood. Light-colored wood is usually oak, ash, maple or birch, while dark-colored wood is usually walnut or mesquite.
  • Determine if the wood is hard or soft by touching it. If you are able to scratch or make a dent in the wood with your fingernail, then the wood is a softwood. Softwood is usually cheaper compared to hardwood and is usually used for decks because it is easy to nail. Some types of softwoods are cedar, pine, and spruce, while, beech and oak are hardwoods.
  • Check the wood’s grain. If it is tight and difficult to see, then the wood is a closed-grain wood. On the other hand, if the grain is large and can be seen easily, then it is an open-grain wood. Generally, softwoods have closed grain, while hardwoods can have both closed or open grain. Ash and oak have open grain, while cherry, maple and alder are closed-grain wood.
  • You can use this information to determine the type of wood that has been used in the construction of your deck.

Which Deck Sealer Should You Choose and Why?

Whether your deck is made from pressure-treated wood, redwood, cedar, cypress or exotic hardwood, the right maintenance and care will keep it in good condition for years to come and sealing is the best way to protect your wooden deck from the elements.

The sealer forms a film which gets bonded to the surface of the wood and provides a high-gloss finish, while at the same letting the natural grain of the wood show through. Sealers are available in water-based and oil-based finishes and form a satin surface that is beautiful and durable.

Cypress Trees on a Cliff

Outdoor wood sealers are formulated with oil or water. Water-based sealers consist of tiny pigments and resin particles that stick to each other tightly like a patchwork quilt when the sealer dries. In the case of oil-based sealers, the particles fuse chemically and form a large sheet, which has a much harder finish.

Water-based sealers are easier to use compared to oil-based ones. They have less odor, they are easy to clean and are less expensive. However, water-based sealers need a greater number of coats and don’t last as long as the oil-based counterparts, which offer long-term protection and durability to the wood.

So, what is the best deck sealer? The best sealer for your wood deck depends mainly on the kind of wood that the deck is made from. It is best to use a clear sealer if the deck has been newly built with high-quality wood.

Clear sealers help to accentuate the beauty of the natural grain of the wood. In the case that you are sealing an older deck or a deck made using pressure-treated wood that has been treated with CCA or chromated copper arsenate, a transparent or semi-transparent stain can help to reduce the leaching of arsenic. A semi-transparent or translucent finish sealer may be ideal if you’re looking for aesthetics.

Wood decks are commonly threatened by water, the UV rays of the sun and growth of mold and mildew and so, it is a good idea to buy a sealer that has in-built waterproofing, UV protection, and mold and mildew protection. 

What is the Best Time to Seal Your Deck?

Age of Your Wooden Deck

If your wooden deck is brand new, it is very likely that the wood has some amount of moisture and until it is completely dry, it will not absorb the sealer properly. So, depending on the kind of wood that the deck is made of, you may have to wait for around 3 to 12 months for the wood fibers to open up. However, if your wood deck is older, you must reseal it once every 12-18 months.

Sunny Outdoors


Most sealers work best in a specific temperature range. Usually, sealing needs 2-4 days without any rain and temperatures below 85oF to ensure that the sealer is absorbed properly and dries completely. The best time to seal your deck is in the fall season since the weather in most places is perfect. 

It is a good idea to avoid sealing your deck when it is snowing or during spring because spring usually brings rain, which means moisture. The presence of moisture can ruin your deck because the wood soaks in the moisture and even if there is no rain, the humidity is sufficient to ruin the sealer.


Before the sealer is applied to the wooden deck, the deck must be cleaned to remove all the dirt and grime, until you reach the solid wood. And, between the time that you clean the deck until the sealer is applied, you need at least around 2-3 days for the deck to completely dry. So, from the time you clean the deck to when the sealer is applied and it dries, you need at least 5-6 days of clear weather. So, depending on where you live, for the best results of sealing, you should choose the driest time of the year in your area.

How to Measure Your Deck to Determine the Sealer You Need

Before you seal your wood deck, it is important to know the total square footage of the deck. When you have this figure, you can decide on the quantity of sealer needed to seal the deck. Typically, sealers are available in 1-gallon and 5-gallon containers and 1 gallon can cover around 200-300 sq. ft. area depending on the thickness of the coat.

So, you will require around 2 gallons of sealer for 500 sq. ft. area deck. Here are some steps of how you can measure the area of the deck you want to seal:

Tools for Work
  • Use a tape measure or a measuring wheel to get accurate measurements.
  • Measure the floor of the deck and take down the length and width.
  • Apart from the main deck floor, add other smaller areas such as a 2nd tier deck, stair landing platforms, etc.
  • Measure the linear feet of the handrails and stair railings and the average railing height. Multiply the total linear feet x height (ft.).
  • Check the number of steps on the deck. Measure the width of the steps. Multiply the total number of steps by the width.
  • Now add the total numbers from the main deck floor, railings and steps. This gives you the total sq. ft. of your deck.
  • Measure and add any extra areas of the deck, benches, skirting, attics, pergolas and other wooden structures that need to be sealed.
  • Once you know the total area of the deck, you can decide on the quantity of sealer required to complete the project. Always buy extra sealer, so that you do not run out of sealer midway during the project. You can either store the unopened sealer for the next time when you need to seal the deck or you can return them to the store.

Steps to Seal Your Wooden Deck

You can buy a sealer for your wood deck from a home improvement store. There are many finish options you can choose from, Generally, opaque sealers are better in terms of their wear- and weather-resistant abilities. However, a lighter finish lets the natural grain and beauty of the wood to show. The clearer the deck sealer, the more frequently you will need to clean and seal the deck.

Tools Required for Sealing Your Deck

Before you start sealing your deck, you must ensure that you have all the tools and supplies needed for the job. Below is a list of things that you will need to seal your deck:

Broom and Dust Pan
  • Deck cleaner
  • Broom
  • Extension handle
  • Garden hose
  • Pressure washer
  • Pole sander
  • 80-grit sandpaper
  • Clear plastic
  • Putty knife
  • Sealer
  • Paintbrush and roller
  • Safety mask
  • Rubber gloves
  • Goggles

Checking Your Deck

Before you start sealing your deck, inspect the area thoroughly. It is a good idea to test the deck and see if it is even necessary to seal it. You can test the deck by sprinkling some water all over the deck. If the water forms beads and is not absorbed into the wood, then the deck does not need sealing. But, if the wood soaks up the water, then the deck needs to be stained or sealed.

Clearing the Deck

Ensure that all the furniture and other items on your deck are removed.

Repairing and Sanding the Deck

Next, you must repair any damage on the deck including repairing the damaged wood, replacing rotten wood and driving nails that may have popped or better still, replacing them with deck screws. Once you have ensured that your deck is in a good physical condition, using a pole sander fitted with 80-grit sandpaper, sand the whole deck. Ensure that every part of the deck is sanded properly.

Sand Paper

Covering the Shrubbery Around

Wet all the plants and shrubs surrounding the deck and cover them using clear plastic sheeting to protect them from the chemicals. Also, cover the siding with paper or plastic before you start sealing.

Cleaning Your Deck

Give the deck a sweep to make sure that there is no dirt or debris from the repair and sanding. Using a putty knife, clean the cracks between the boards. Unless the deck is brand new, you will need to clean the wood surface with a high-quality deck cleaner to prepare it for sealing.

A good-quality deck cleaner with help to remove all dirt, grime, mildew, and algae from the wood. Some cleaners require the deck surface to be damp, while others need a dry surface before applying. Check the manufacturer’s instructions before using the cleaner.

Using a garden sprayer, paint roller or a stiff-bristled broom, apply the cleaner on the entire deck and do not let the cleaner puddle in one area. Using a broom or a stiff brush, scrub the tough areas. Avoid using wire brooms or brushes, as the wire bristles can break off and can produce rust spots. Let the cleaner soak into the wood. Do not let the cleaner soak for more than 10 minutes; however, check the cleaning product instructions.

You can use a garden hose to wash down your deck. Alternatively, you can use a power washer; however, ensure that you use a good fan tip along with it to prevent the wood from getting damaged. Rinse the deck thoroughly. Before applying the sealer, let the deck dry completely at least for 2-3 days.

Working with Wood

Applying the Sealer

Checking the Weather

Once you have prepared the deck’s surface, it is time to apply the sealer on the deck. However, before you actually start the process, check the weather and ensure that you have at least 2-3 days of dry weather to apply the sealer and let it cure. The best temperature to apply the sealer is around 51oF to 89oF.

Reading the Product Instructions

It is extremely important to read all the instructions that are provided along with the sealer. When applying the sealer, follow the instructions that have been provided with the product closely.

Stirring the Sealer

Prepare the sealer according to the product instructions. However, avoid shaking the sealer. This can cause bubbles to form in the sealer. Instead, mix the sealer well by stirring it properly.

Applying the Sealer

Avoid applying the sealer in direct sunlight because it will dry too fast and will not be absorbed into the wood’s surface. Cover a 2-board section of the wood with a thin coat of sealer either by using a roller fitted with an extension handle or a roller. Always apply a thin coat of sealer instead of an extremely thick coat. Avoid applying more sealer than what can be smoothed out before the product dries.

It is always a good idea to get someone to assist you with the sealer application. Ideally, one person can apply the sealer, while the other smoothens it out to prevent the formation of puddles. Do this until the entire deck’s surface has been covered. You can apply the sealer in corners and other areas like railings, steps, cracks and end grain by using a paintbrush.

Applying a Second Coat (Optional)

Once the sealer has dried, if you want, you can apply a second coat of the product. However, you must ensure that the coats are applied uniformly and you must also move at a steady speed just as you did earlier.

Rinsing and Removing the Plastic Sheeting

Rinse the plastic covering your plants and shrubbery with water and remove it.

Relaxing Outdoor Setup

Allowing the Deck to Completely Dry

Now, you must allow the deck to completely dry. Once it has dried, you can move back all the furniture and other items onto the deck and sit back and enjoy all the hard work you have put in.

Exposed to harsh weather, sun and foot traffic, your outdoor deck takes a beating all-year-round, making it susceptible to stains and damage. Application of a waterproof sealer once every 1-2 years can keep your deck in “as good as new” condition. Keeping your deck clean and dry and maintaining it throughout the year can help to preserve its beauty for years to come.