Do I Need to Seal my Painted Wood for Outdoor Use?

Do I Need To Seal My Painted Wood For Outdoor Use?

You refinished or built a deck, you slapped on some paint after spending hours deciding on a color that contrasts the shutters, and now it’s done.

Congratulations! If you don’t seal that wood, though, you’re about to watch a lot of hard work and energy drip down the drain.

Failing to seal painted wood is one of the cardinal sins of outdoor DIY work. Wood is porous, and easy to destroy with water damage, so a few rainstorms in and you’re going to run into serious problems. Paint will run, colors will fade, and time will be wasted.

This is how to seal painted wood for outdoor use and make sure it retains its shiny new coat, and doesn’t warp or split. We’re about to kill two birds with one stone.

What is Wood Sealing and How Does it Help Wood?

First off, wood sealer is a product that creates a strong bond and barrier on the exterior surface of wood. If you didn’t know, wood is a naturally existing polymer. It doesn’t matter which tree it comes from, or if it’s treated or not, it doesn’t change what it is.

When you cut wood, you create rough edges along the natural fibers that bind wood together. Cut a piece of wood and just gently graze your hand along the cut portion; you can feel a low-grit sandpaper-like finish, depending on what cutting method you used.

Those are all pathways to invite water inside of the wood, which can lead to rotting. When wood rots, it breaks down the molecular bond between polymer cells, and essentially becomes brittle and frail.

So can wood get wet?

Yes, it can, but it needs to be able to dry efficiently, otherwise that moisture sits and causes problems.

Wood actually has to have a specific moisture content (depending on the type of wood), but by sealing it, you’re locking in the moisture that it needs, and preventing more from entering through the pathways in these natural fibers.

It helps wood by preventing rot, but it can also prevent color fading on painted wood, and degradation or breakdown due to UV light. UV light can break down even synthetic polymers, like plastics and rubbers, so imagine what it can do to something organic like wood.

Is Sealing Wood Necessary for Outdoor Use?

Yes, sealing wood is absolutely necessary if you care how your outdoor wood looks and reacts, even in the slightest. You’re reading this, so I have reason to believe that you want your deck, fence, or porch to actually make it through the years with minimal wear and tear. You want it to last.

These are all the reasons that you absolutely have to seal your outdoor wood if you want it to last in the slightest.

Maintains a Waterproof Barrier

When water seeps into your deck, it can cause some serious, long-term damage. It’s not immediate, but as we’ve come to find out, it can still leave permanent damage that could result in wood rot and eventually having to replace that wood.

When you seal your wood, you get it ready for incoming rainstorms, humid days, winter, and everything that could mess with the moisture inside of your wood.

Wood already contains a certain amount of moisture, depending on the specific type of tree it came from, but we don’t want to bring it outside of its acceptable parameters.

Keeps Wood at the Right Moisture Level

Moisture level matters. If your wood was completely dry, it would crack and break with absolutely no malleability.

However, too much moisture is when you start to run into rot, and structural damages. That’s what we want to prevent from happening. A barrier works two ways: it keeps out what you don’t want, and keeps in what you do want.

Winterizes Your Deck

Winter comes, and it hits your deck hard. When snow begins to melt, it just continually feeds water into your deck with no direct sunlight to help evaporate it quickly.

Without a properly winterized deck, the moisture that is still contained in your wood (usually 9% up to 13%) can freeze as well, making splits and divots in the wood even deeper as the ice expands.

This will also make shoveling easier, because you won’t have stubborn slush sticking to the little nooks and crannies of your deck all the time.

Reduces Color Fade by Over 90%

Your siding is a specific color, so you anticipate that you want the same color for your shed, or your deck in the backyard. Who wouldn’t want that? The problem is, that color isn’t going to remain if you let the sun ravage the surface of your wood.

UV rays will break down whatever the paint is actually made of, which is usually a synthetic polymer (known to break down from UV rays), unless there’s that barrier in between.

The barrier of sealant is broken down by UV rays instead, since this can’t be avoided, but it preserves the coloration and the actual paint or stain on your deck. That’s why replacing this sealant layer is absolutely necessary.

Prevents Structural Damage

When wood constantly expands and retracts due to moisture, it weakens the bond between the fibers. This can take a while if the water damage is just rain-related and the wood is not entirely submerged.

You might not notice this for a few years if you live in a rainy area and do not seal your deck. Part of this depends on the grade of wood used in the deck, although all wood will eventually degrade if left unchecked.

When this happens to banisters and support beams on your deck, it can cause an actual hazard that could result in fairly serious injuries. Those are extreme cases, of course, but they happen all the time.

Maintaining your color, the integrity of your deck, and preventing structural damages over time are all extremely important for the future of your deck.

How to Seal Your Painted Woods for Outdoor Use

The number one issue people make with sealing their deck is not doing it to fresh wood.

If you purchased a home with an older deck, that’s totally fine, you just have to know that the deck has already seen its fair share of weathering. Older decks are almost never taken care of properly, so the task is left up to you.

We want some light, high grit sanding across the surface of the entire deck. Just enough to take away some of those weathered elements. What happens here is that you create new entryways for the naturally existing fibers of the food; it’s like opening the lid on your deck.

This allows you to apply your sealer. You can paint first if you’d like, or stain, but when it’s time to apply your sealer, get a paint roller, a paint brush, and a paint tray ready to go.

Use a roller to get the surface of your deck, applying in nice even strokes.

You want a little excess sealer on the roller so that it can get in between those little crevices (usually about ⅛”) of your deck boards. You can’t sand every single surface area on every piece of wood, but you can get this covered as soon as possible.

Use a hand sander for banisters and railings, and then the paint brush to apply stain to all surfaces of the wood. The biggest thing with a sealer is making sure you hit your deck from every angle to protect it fully. If you miss one area, it can still be damaged by rain and moisture.

Is There a Difference Between Stain and Sealer?

Is There a Difference Between Stain and Sealer?

Yes, there are differences. You might have found that some deck paint is going to say that it includes sealer, or that it’s a sealer and stain combo. Those are true, because you can have both of them meshed together. Both can even be effective, if you really look at them.

The main differences are as follows:

Water Resistance

A deck stain normally does have the same water resistance rating as a sealer, but doesn’t provide the same level of barrier.

This basically means that it will be able to help you repel water, but resisting water is different from completely preventing it from penetrating the surface. Think of IPX waterproof ratings.

They have different numbers to let you know what can and cannot be submerged based on how waterproof something is. Think of a stain as something that helps repel light rain, but in heavy rainstorms, it won’t hold up as well.

A deck sealer is there to prevent just about any amount of water from sitting at surface level for too long to the point that it can grow fungus and potentially eat through your wood.


Stain is there to stain the wood and permanently change its color. Stain will hold up against UV rays better than wood paint, so if you exposed them to the exact same conditions, stain would retain that color change for longer periods of time.

However, it will still break down. Sealant acts like cannon fodder: it ends up being destroyed by UV rays over time so that your cloration doesn’t fade. Stain will show wear and tear with time, but with proper sealer use, you won’t notice that on your other outdoor wood very much at all.


You will need more sealant than you will need stain. Sealant generally goes on with a light syrupy consistency, while stain will be a little bit thinner.

This is because it needs to have enough of a liquid consistency to actually soak into the wood and stain it, as well as provide that top layer of protection.

Long Live Your Aesthetic Outdoors

Your deck, shutters, fence – what it is that you built – is going to last you for years to come. And now, the coat of paint you chose is going to last for just as long.

Sure, you might need to paint a touch-up once every ten years or so, but as long as you’re sealing your painted wood for outdoor use, you’re doing a serious service to your home.

We’ve compiled a list on the best sealants for composite and wood decks, sheds, fences and more in this comprehensive guide. It’s time to seal the deal.

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