How Much Does it Cost to Seal or Waterproof a Deck?

A beautiful wooden deck needs to be sealed every few years to keep it beautiful. In some climates it can need it as often as every season. Staining and sealing your deck will help preserve it against the elements and is part of regular maintenance. A regular schedule will do wonders for keeping it looking new, preventing fading, and keeping the wood from splintering. There are a few basic cost factors when it comes to staining and sealing a deck.

On This Page:

1. Sealing vs. Waterproofing Your Deck
• Why Waterproof?
• Sealing Products & Costs
• DIY Cost Considerations
2. Deck Refinishing
• Labor Costs
3. Cleaning & Sanding a Deck
• Power or Pressure Washing Costs
• Sanding the Deck & Its Costs
4. Conclusion

Sealing vs. Waterproofing a Deck

When choosing between stain and sealer, deck professionals will recommend not to stain horizontal decks because cracking and peeling occurs more quickly because of the sun’s rays. In such cases, you might do a two-toned deck with stained railings and a deck floor with only sealer. If you stain the deck floor, you will need to reseal it every two years to prevent cracking and peeling. The costs to apply sealer or both stain and sealer are:

• $300 to $400 for a 250 square foot deck. Add in staining for $400 to $600 total.
• Two gallons of sealant: $50 to $80

When you decide to seal your deck, it’s imperative to know the difference from staining. Sealing protects a deck from moisture, which can lead to mildew and mold buildup. Stains are used to change a wood’s original color, although some types can protect the wood as well -- not as well as sealer, though.

If you decide to apply sealers in place of or addition to stains, you can choose from a couple types:

• Oil-based – Oil-based sealers are either penetrating or coating, or may be a bit of both. Penetrants will sit right at and just beneath the surface of the wood. Coatings sit on top of the wood. A sealer that does both is considered a coating sealer whether it is 10% coating with 90% penetrant or a full 100% coating. Also, any sealer that contains linseed oil is a coating. Coatings need to be stripped before new sealer is applied, but penetrating sealers can be applied over old applications after a good cleaning.
• Water-based – Water-based sealers are coatings. They clean up easily with soap and water, making them very attractive to the DIYer, but they are less resistant to wear and tear from normal use than oil-based sealers. They can be harder to work with and maintain when used with oil-based stains, but are more environmentally friendly.

Wood sealers can be applied with a brush, a roller, or a sponge. Every sealer will have different instructions, so pay attention and follow the manufacturer’s directions. Because you won’t be able to see where you have put the sealer, develop a pattern to know where you have and haven’t sealed. The only sealers that you can see where you’ve been are primer types. Most sealers will require two coats to properly soak in and provide optimum protection.

Your deck should be cleaned before applying a sealer.

• Good quality oxygen bleach mixed with warm water should be brushed onto the surface.
• The surface should then be scrubbed with a long-handled brush to remove any mold, algae, or leaf debris.
• The wood should then be inspected for damage or rot that may have occurred since its last treatment.
• Take advantage of this time to replace any damaged boards.
• Once the deck has thoroughly dried you can apply the sealer.

Why Waterproof Instead?

Sealers provide a degree of waterproofing, but it’s better to put a layer of waterproofing over your sealer, especially if you live where it rains a lot. Sealers work by getting into the wood and preventing moisture from staying in the pores and forming mold and mildew. But does your deck really need waterproofing as well?

In a nutshell, yes. You’re not only protecting your deck, you’re protecting your home as well. A deck that cannot shed water will form a large area of moisture and dampness sitting right up against your house. This will cause mold and mildew to form not only on your deck (the sealer will gradually fail from being essentially submerged), but also on your walls and foundation. Waterproofing your deck helps water cascade off of it and away from your house.

Some types of waterproofing use oil that sits on top of the wood and repels water. Others use a polymer or resin in a solvent that evaporates and leaves a solid layer of waterproofing material behind.

• Epoxy resin - One of the most important things to consider with epoxy resin waterproofing is the curing time. A product with a fast curing time might not be suitable for a large surface area. It could dry and harden before you have time to smooth out any trouble spots that may have formed. Too long a curing time and you won’t be able to enjoy your cozy little deck for some time until it fully cures.
• Oils – Natural oils such as linseed oil and tung oil penetrate the wood to some degree, with tung oil performing slightly better. Some synthetics perform even better than tung. This provides sealing as well as some waterproofing. While they give wood a natural look, they take more work to apply as they need to be rubbed into the wood over several applications. Regular treatments are needed every 6 months to a year.
• Varnish – Varnish provides excellent waterproofing. After all, they use it on the decks of boats, don’t they? You might be tempted to use it on your backyard deck as the ultimate in waterproofing based on this, but you may want to think twice. Varnish, especially marine varnish, is very effective against an onslaught of sea spray and other high moisture areas, such as near a lake, but it can be slippery when wet. It also doesn’t hold up well in dry or high-heat regions. If you have a cedar deck, look for a varnish specially formulated for cedar to bring out its best appearance. For hardwoods, a single coating of varnish is usually enough, but softwoods could take 2 or 3 coatings.

Sealing Products to Choose From

If you decide to use combination products, it’s best to talk to a professional or to someone else who has a deck that sees the same kind of use and conditions as yours. Getting real-world information before you refinish your deck is invaluable. There are good combination products out there, and as in all things price is no guarantee of quality, but in general the lower-priced options are often the thinnest and least durable. You can pay anywhere between $20 and $50 per gallon to waterproof your deck. Here are some of the more common brands that both contractors and consumers use:

• TWP – TWP (Total Wood protection) offers a full line of stains, cleaners, sealers, strippers, and brighteners. They may be harder to get for some people as some products are not VOC compliant. $30-$40 per gallon
• Behr – Behr is one of the leading brands of stains, sealers, strippers, cleaners, and finishes. Known mostly for their paint products, their wood products are a popular choice for many DIYers. $20-$35 per gallon
• Thompson’s WaterSeal – One of the most recognizable names in waterproofing and other exterior wood care, Thompson’s WaterSeal is also noted for preserving the decks at Niagara Falls. Most of their products meet or exceed VOC compliance standards. $14-$30 per gallon
• DEFY Wood Stain – DEFY, owned by SaverSystems, offers a line of stains and cleaners designed to take a beating. However, locating a nearby dealer might be a bit hard, so it’s also available online. $20-$45 per gallon
• Armstrong Clark Stain – Armstrong Clark is VOC compliant in all 50 states and works well even with tropical hardwoods such as Ipe and Tigerwood. $40-$50 per gallon
• Sherwin-Williams – Sherwin-Williams has been around a long time and has an excellent track record for outdoor wood products. Its claims of durability have held up under numerous reviews, and one coat usually does it. $40-$50 per gallon
• Olympic – Olympic has been around since 1938 and offers stains, cleaners, and resurfacers. There’s a product for every price range, making it popular with DIYers and contractors alike. $25-$45 per gallon

DIY Considerations

If you decide to restore your deck yourself, the stains and sealers can cost between $20 and $40 per gallon. Waterproofing costs between $10 and $20 per gallon. Now add the tools you will need (buckets, brushes, rollers, etc.), and you can add another $20 to $40. Remember that stains and sealers will require multiple coatings, and a gallon only covers so many square feet. For example, one gallon of stain covers an average of 300 square feet, one gallon of sealer usually covers 200-300 square feet, and one gallon of waterproofing covers 100-200 square feet.

One thing about DIY staining and sealing is that while you may save yourself the labor costs, you run the risk of applying it improperly. Miscalculating how much you need of a stain or sealer can leave you running back to the store for more while your project dries or cures unevenly. Sometimes this leaves permanent flaws in your deck because you couldn’t clean it up while it was still wet.  

If your deck is in bad shape, you’ll have to rent a power sander, and if you don’t know how to use it properly you can leave burn marks on your deck, uneven spots where you sanded too much, or you might end up damaging the machine and being responsible for any charges.

Deck Refinishing

Deck refinishing is a fairly complex job that can take up a whole weekend if you have a large or elaborate deck. It’s not as simple as sanding and then re-staining and resealing.

1. A deck must be cleaned of any debris. This includes the spaces between the boards and any space between the deck and your house where dirt, leaves, pine needles, etc. can get trapped. Cleaners, some with bleach or certain acids, are used to remove discoloration from water damage and other stains. Though you can use a regular water hose, a pressure washer will yield better results and is indispensable for any homeowner for a number of reasons.
2. Inspect the boards and fasteners. Nails can pop up and cause tripping or injury hazards, especially for bare feet. Hammer them back down making sure the head is slightly below the surface of the wood.
3. Apply the new sealant over the top of the old one. If your deck is heavily damaged, scratched, or stained, you may need to remove the top layer of wood. Be sure to check for popped up nails as they can cause damage to your sander, your sand belt, and to anyone nearby if the belt breaks and sends abrasive sand paper flying.
4. Strip the deck if you’re going to apply new stain. Leaving any old sealant behind will prevent the new stain from getting into the wood. Chemical strippers combined with a pressure washer will effectively remove old stain without altering the surface of the wood (such as sand-blasting can do), but make sure your surrounding landscaping is covered. Once the deck has been stripped, you can apply new stain and sealer.

If you have used pressure treated wood, check with the supplier before you restore your deck. They may require a waiting period of one month to a year before sealer can be applied due to the chemicals used in the treatment.

Labor Costs

The cost to restore your deck yourself versus the cost of having a professional refinish it typically isn’t that much of a difference. Even with average labor costs of about $30 per hour, a 250-square-foot deck has a cost difference of about $100 to $150 depending on the quality of stain and sealer you use.

For some people, it’s worth hiring a professional to make sure it’s done right. The per-square-foot charges can start between $0.50 and $2.50 depending on the condition of the deck, but can go to between $2.50 and $7 if you have multiple levels, spindles, stairs and other features.

Some services will offer separate quotes for cleaning and staining. Also, the quote may or may not include removing furniture and other items from the deck. Be sure to ask what the quote involves.

Should I Clean Or Sand My Deck First?

Cleaning your deck before refinishing it is critical. If you don’t remove dirt and debris, you’ll be locking these moisture-trapping elements into your deck. This will keep any new sealer from doing its job and lead to failure and costly repairs. Cleaning also gives you the chance to examine the boards, railings, spindles and stairs for any damage or trouble spots.

Power or Pressure Washing

While many stores and supply houses use the two terms interchangeably, they are two different techniques and are used for two different types of cleaning.

• Power washing uses a steady stream of hot water. It comes out very strong and is most frequently used for ground-in stains, mold, mildew, moss, and other hard-to-remove materials.
• Pressure washing uses a much stronger force of water, but doesn’t use hot water. It relies on the pressure of the water alone. It’s best used for surface dirt and stains and is generally faster than power washing.

You can buy a power or pressure washer for $100 to $200. Higher-powered washers can also be rented, but the price can vary from a flat $40 per hour to $70-$80 and more per day. Often, prices can vary due to the washer itself. High-powered models go for more than lower-powered ones, and brand names, like Briggs & Stratton or John Deere, can affect rental prices.

Though buying a power or pressure washer makes more sense, there are reasons that you may not want, or be able, to do it yourself. Time constraints, physical handicaps, or a deck that’s just too big or complex can make it better to call a professional.

Hiring a service usually includes staining and sealing, and this basic level of refinishing runs between $0.50 and $1.50 per square foot. If you do it yourself, be aware that improper use of either tool can raise the grain of the wood. Many services recommend that you use a brush and an ordinary water hose if you aren’t sure about it.

Sanding

Sanding your deck should be done if the deck is damaged, scratched, or heavily stained. Sanding removes the top layer of wood and can be done with a power sander or with blasting media.

• Power sanders require a degree of skill and know-how to use properly. It’s possible to burn the wood if you stay in one area too long, and while an opaque stain can cover this, you also can put divots and valleys in your deck by sanding away too much in one spot. These imperfections will allow water to pool up and cause your sealer to fail.
• Blasting media takes a high degree of skill to do it right when working with wood. It’s not something that just anyone can, or should, do. The risks of ruining the deck are very high in the hands of someone who doesn’t blast decks for a living. However, for some deep or dark stains, it could be the only way to get rid of them without refinishing in a solid stain or paint.
• Blasting services can cost $40 to $65 per hour or around $860. Some specialty blasting services can cost $75 per hour. The blasting medium can cost $50 per 50-pound bag.

Whichever method you use, cleaning the deck first is an absolute must. Removing the old sealer is vital if you are going to restain your deck. Leaving the old sealer on will prevent the new stain from penetrating the wood. If you’re not going to restain your deck, you can apply new sealer on top of the old one. It will settle in on top of the old layer and take over its job.

Conclusion

Refinishing or restoring your deck is a worthwhile task whether you do it yourself or hand it over to the pros. A deck adds value to your home and provides a wonderful outdoor space to relax or entertain, but only if it’s properly maintained. This basic, if involved, maintenance should be done every 1 or 2 years and can allow you and your family to enjoy your deck for a long time.