Seal/Stain a Deck whenever it Fails the Bead Test


Wood decks are the most economical deck and can last for years with regular maintenance. The key is correctly caring for the wood. Sealing is one of those essential wood care items. How often does a wood deck need to be sealed?

A wood deck needs to be sealed every 1-3 years, depending on sun exposure, use, and quality of sealer. A simple water bead test will confirm if the decking needs to be resealed. A wood deck will be better protected if its stained regularly with a quality stain instead of just sealed.

It’s a matter of how it responds to water. I will explain that more, but the simplest test is the water bead test. Dip your finger in some water and sprinkle it on your deck. If the wood readily absorbs the water, it needs to be sealed. If small droplets of water form on the wood, it doesn’t need to be sealed. It is that simple if the water is repelled, the wood is sealed.

One qualifier, if the wood is already saturated with water, water will bead off the surface. Therefore, only test your deck after a few sunny days, allowing the wood to dry.

Why does exterior wood need to be sealed?

Glad you asked. You paid extra for treated lumber and decking, why does it need to be sealed? There are a few reasons that the deck should be sealed.

“Pressure-treated wood is wood that has been infused with chemical preservatives to protect the wood from rot and insects. “

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Your new deck is only treated to make the wood inedible to insects and fungi. It is not treated to protect it from water. Wood needs to be sealed to protect it from water damage. If not sealed, the wood can still become saturated, making it vulnerable. Sealing wood helps to minimize excess saturation, the swelling that makes wood soft and easily damaged.

Notice how mud tracks are formed in the dirt only after a rain? When the ground is wet, saturated with water, tracks imprinted across the ground. The same walking that when the ground is dry, will do nothing. The same is true with wood. When wet, it easily damages, but when dry, it is durable.

Dragging a chair across a wet deck will leave a mark where a dry deck will be unmarred. Sealing your deck helps to keep the decking dryer even when it rains, reducing surface damage.

Sealing wood also helps to protect it from extreme changes in moisture. Unsealed wood will soak up the rain, increasing in size. Then the sun comes out and quickly dries the surface of the wood, squeezing the swollen internal wood. This stress causing the wood to crack.

“Moisture swells the wood while the burning rays from the sun dry and shrink it, causing cracks and checks while also encouraging warping.” 

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Sealing helps to keep the moisture level consistent throughout the decking. The heart of the wood having the same level of moisture as the wood’s surface. The sealing, slowing down water absorption.

Decking is only surface-treated

Another reason and sign that your deck needs to be resealed are wear paths on the deck. We have all seen it, a walking path over a deck where the brown treatment has been worn off. Exposing the wood to water and rot as the treatment has been worn off. Wood treatment is only surface deep. When it is rubbed off from use, it becomes the same as untreated wood.

This path, along with the entire deck, needs to be resealed to restore its protection. A hole worn in your jeans will not protect you from the wind and rain. The same with your decking. When a “hole” has been worn in the treatment the wood is no longer protected.

I hope you are convinced that your wood deck needs to be sealed to increase its life. Raising the question.

How Long Should you wait before Sealing Pressure Treated Decking?

I have heard from a few days to wait at least one season before sealing a deck. Sadly, I must admit that over the many years of building decks in Calgary, I to have varied in my answer. But the more research I have done on the question, I have come to this conclusion.

A wood deck can be sealed a few days after framing. If the weather is dry and the forecast is good, sealing your deck sooner is better then later. The argument why you should wait is to allow the wood time to climatize and dry out. Fair enough but all wood sold has been dried to 19% humidity, the magic moisture level that prevents wood rot. Fungi will only grow in wood with a moisture content of higher than 19%. So, if you were to seal the wood at that level, no harm will result as it is dry enough to prevent rot.

Waiting a few days after completing your deck will ensure that any extra water that got on the lumber in storage will evaporate out. If you are still concerned, do the water bead test. If the wood is to wet to be sealed, the water will bead on the surface. Give it a few more days to dry, then test again.

Or you can buy a moisture meter, costing between $50 to $100 depending on features and manufacturers. Check to see if the moisture content is higher then 19%. An advantage of a moisture meter is an accurate number to base your decision off.

Another way to access the moisture content of wood is a trick I learned from WilliamOpens in a new tab.. Sorry, I only know his first name. Let’s call it the sweat test. Wrap the decking with a black plastic bag and let the sun warm it up. After a couple of hours, unwrap the bag. If there is condensation on the bag, then there is still excess moisture in the wood. If the bag is dry, so is the wood. Only wet wood can “sweat,” as the moisture is drawn out of the wood with heat.

 “Sealant also prevents the wood from drying to fast which will cause excessive warping”

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Sealing your deck sooner instead of later will help to protect the deck from early damage. As the sealing will slow both water saturation and drying of the wood. Leaving the decking untreated for a year only increase the time that it can be damaged by the sun and rain.

Speaking of damage caused by the sun and rain. A wood deck should not only be sealed but stained.

Staining a deck is better than only Sealing it.

We often refer to it as weathered, when wood becomes discoloured and frayed. A beautiful rustic look but not good for a deck. This is caused by damage from the sun and wind.

“Ultraviolet rays also discolor wood and accelerate wear by breaking down wood fibers.”

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You can prevent this damage to your deck by staining it. Sealing a deck only repels excessive water but does nothing against the sun’s harmful rays. Staining a deckOpens in a new tab. not only protects it against the rain but also the sun. The pigment in the stain penetrates the wood, protecting against harmful UV while repelling water.

“The primary function of a sealer is to repel moisture.”

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When the deck is only sealed, its colour will begin to fade in only 3-6 months. Requiring regular application but stains with the increase pigment and protection can last up to five times as long as a sealant. Allowing longer periods of enjoyment between application. Some stains warranty 3 years of deck protection. Much longer then any sealant can promise.

Not only does stain better protect your deck than sealer only, but it also adds vibrant colour to your deck. Personally, I like the transparent or semi-transparent stains allowing the beauty of the wood to come through while still protecting it for years to come. But solid or Opaque stains with an increased level of pigment will actually protect the wood longer from UV damage — a fine balance between beauty and function when selecting decking stain.

So, if stain is better, then sealer and solid stain colour protect. What about paint?

Can I paint a deck instead of stain?

No, now you have gone too far. A solid stain will protect a deck better than paint. Stain penetrates the wood, becoming one with it. Paint covers the wood, like a blanket or sweater covering the wood. This sounds like a good idea except that as wood and paint expand at different rates. This conflict causes the paint to chip off as it no longer “fits” the decking. Flaking off, looking ugly, while decreasing the protection of the wood.

If this ugliness wasn’t enough, paint lies like a thick blanket over the decking, trapping moisture in the wood. Doing the exact opposite of stain and sealer, instead of repelling the water, allowing the wood to stay dry, it straps moisture increasing moisture levels. Causing the decking to rot underneath the paint. When the paint starts to flake of, not only does it look ugly but it reveals rotten wood underneath.

“Take care of your deck, stick to stain.”

Ryan, the deck guy

Another way to look at it is. Paint on a deck is like a plastic “tattoo” sticker on your arm. Looks great initially but will soon wear off in patches all while uncomfortably trapping water and restricting your skin. Stain is the real tattoo; the ink is injected into the material. The ink and wood become one, it may fade many years down the road, but it has become part of you and your deck. If you want it to last, penetrating will always be better then surface level.

A big part of deck maintenance is keeping it clean. Removing any dirt that builds up on the deck and between cracks trapping moisture causing rot. Even better then sweeping the deck off is washing it down with a pressure washer.

But, Do I have to seal my deck after pressure washing?

Well, that depends on what pressure you spray the deck at. Over 1 000 psi will strip stain on a deckOpens in a new tab.. If you wash your deck down at that level, be prepared to stain it after as the wood will no longer be sealed. Even if it doesn’t strip on the stains, holes where your nozzle sprayed to hard will weaken the decking protection requiring it to be resealed again.

Top Rated Electric Pressure Washer

Keeping the pressure washer around 600 psi or a spray nozzle on a garden hose will clean your deck without requiring resealing, but if you go too hard. Yes, it would be best if you resealed a deck after pressure washing.

It’s a good idea when pressure washing to keep the wand 3-6 inches away from the decking. Going any closer increases the water pressure hitting the deck which not only can remove the stain but also rip off layers of wood in seconds — creating an ugly dip in the decking. Its fun using a pressure washer but care must be taken for your not causing damage while cleaning the deck.

If you do decide to re-stain your deck, here are a few pointers.

Preparation before staining or sealing a deck

Before grabbing the brushes, a deck needs some preparation work before staining. The entire deck needs to be clean of mud, leaves, branches, anything that will hinder stain from penetrating the decking. If previously sealed all the old sealer will need to be removed to allow the new stain to be absorbed consistently. Hate to spend all the time re-staining to have splodge staining. Old stain can be removed with chemicals like sodium hydroxide-based strippers, but care must be taken as it can damage both cedar and pine, both common decking materials. Always rinse thoroughly to remove all chemicals from the decking to prevent damage.

The use of deck cleaner will help to remove rust stains, grim and other blemishes from the deck surface.

Do you have to pressure wash a deck before staining?

Before staining a deck, all the grayed layer of oxidized wood needs to be removed. Removal can be done either with a pressure washer or sanding. Either one will require care in not to remove too much material, leaving deviates in the decking.

Pressure washing needs to be between 1000 -2000 psi, consistently holding the fan 3-6 inches away from the decking, carefully removing damaged wood. Pressure washing can leave behind small fuzzy hairs of wood. These fuzzies will not impact the staining process and will wear off in two to three weeks. One of the advantages of pressure washing is the removal of all material stuck in the wood cracks providing a clean surface to stain.

A possibly better alternative is sanding down the deck before staining. Starting with 150 grit sandpaper and increase grit till is efficiently removing the oxidized wood. Do not use any heavier grit then 60. 60 grit and heavier sandpaper will tear the decking up. The advantage of sanding is it flattens and smooths out decking better while removing the old sealer better than pressure washing.

Leave sufficient time for the wood to dry after washing. Remember, you want the wood to be less than 19% which will require a couple of days of drying after washing. Another advantage of sanding is no drying time is required.

Temperature of the decking is very important when staining. Avoid staining in direct sunlight in the heat of the day, rather seek days with a temperature between10°C (50°F) and 32° (90°F) for at least 24 hours during and after staining.  

Early Spring or Fall is the ideal time to stain a deck.

As the temperature is more moderate and consistent, giving you the greatest window of opportunity for staining. Personally, I prefer deck staining to be part of spring cleaning. Then you can enjoy your clean, sealed and beautifully stained deck all summer before snow and iceOpens in a new tab. take a toll on the decking.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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