Exterior wood fails in a specific order, and knowing the order tells you what a sealer actually has to do. First UV breaks down lignin, the polymer binding the wood fibres, and the surface greys. Then water cycles in and out, swelling and shrinking the fibres until the surface checks and splits. Then fungi colonise the damp, damaged surface. Rot is the last stage, not the first.
A sealer that only repels water addresses the second problem and ignores the first. That is why clear sealers grey out and need reapplying annually, while pigmented finishes last three to five years — pigment is the UV blocker, and there is no clear substitute for it.
Our Top Picks
- BEST ALL-ROUND CHOICE FOR MOST EXTERIOR WOOD: Ready Seal Exterior Wood Stain & Sealer
↓ Jump to Review - WATER PROTECTION ONLY, NO UV DEFENCE: Thompson's WaterSeal Clear Wood Sealer
↓ Jump to Review - LONGEST LIFE, GRAIN HIDDEN: DEFY Solid Color Wood Stain
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The Finish Spectrum
| Finish | Pigment | Grain Visible | Typical Life | Reapplication |
|---|---|---|---|---|
| Clear water repellent | None | Fully | 1 – 2 years | Clean and recoat |
| Toner / clear with UV blocker | Trace | Fully | 1 – 2 years | Clean and recoat |
| Semi-transparent stain | Light | Mostly | 3 – 5 years | Clean and recoat |
| Semi-solid stain | Medium | Texture only | 4 – 6 years | Clean and recoat |
| Solid colour stain | Heavy | Texture only | 5 – 7 years | May need stripping |
| Exterior paint | Opaque | None | 7 – 10 years | Scrape and repaint |
| Marine varnish | Clear, high UV package | Fully | 1 – 2 years exterior | Sand and recoat |
Two further distinctions matter as much as the pigment level.
Penetrating vs. Film-Forming
Penetrating finishes — most oil-based and many modern water-based stains — soak into the wood and leave no surface film. They wear away gradually and evenly, which means reapplication is a clean-and-recoat rather than a strip. Film-forming finishes — solid stains, paints, varnishes — sit on the surface, last longer, and fail by cracking and peeling, which means eventual stripping.
On horizontal surfaces that hold water and take foot traffic, penetrating finishes are almost always the better choice, because a peeling film on a deck is a far worse maintenance problem than a faded penetrating stain.
Oil-Based vs. Water-Based
Oil-based finishes penetrate deeper, wet the wood better, and are more forgiving of imperfect surface preparation. They are also slower drying, higher in VOCs, restricted in some jurisdictions, and they provide a food source for mildew unless the formulation includes a mildewcide.
Water-based finishes have improved substantially. They resist mildew better, hold colour longer under UV because modern acrylic resins are more UV-stable than linseed oil, clean up with water, and dry fast enough to apply two coats in a day. They are less forgiving of a damp or dirty substrate and can raise grain on the first coat.
Choosing by Project
Fences
A fence is mostly vertical, sheds water quickly, and takes no traffic — which means UV is the dominant failure mode and water is secondary. That argues for a pigmented semi-transparent or semi-solid stain, and against clear sealers, which will grey the fence within a season or two despite being applied.
Fences are also large, so cost per square foot matters and spraying with back-brushing is the practical application method. Budget-conscious pigmented stains sold in five-gallon pails exist precisely for this job.
Redwood and cedar fences deserve a note: both contain natural extractives that give them rot resistance and colour, and both grey rapidly without a UV-blocking finish. A semi-transparent stain in a tone close to the natural wood preserves the appearance people paid extra for.
Outdoor Furniture
Furniture is handled, sat on, and looked at closely, so appearance and feel matter more than on a fence. Penetrating oil finishes give the richest look and the most tactile surface, at the cost of frequent reapplication. Film finishes last longer but show wear at contact points.
For teak specifically, the calculus is different — teak's own oils make it rot-resistant untreated, so finishing is purely a colour decision. Our teak oil versus sealer comparison covers that in detail.
Decks
Horizontal, wet, walked on, and the hardest exterior wood application there is. Penetrating semi-transparent stains are the consensus choice: they wear rather than peel, they carry enough pigment for real UV protection, and they can be recoated without stripping. Solid stains and paints on a deck surface look good for two years and then peel in traffic lanes.
Marine and Waterfront
Salt and constant UV make this the most demanding exposure. Marine-grade products carry heavier UV absorber packages and are formulated to stay flexible as wood moves with humidity. If wood is within a few hundred yards of salt water, the marine product is worth its premium even on a garden bench.
Pressure-Treated Lumber
New pressure-treated wood is often too wet to accept a finish. The treatment process saturates the timber, and applying a sealer before it dries traps that moisture. Test by sprinkling water on the surface: if it beads, the wood is still too wet; if it soaks in within a minute or two, it is ready. That can be anywhere from a few weeks to several months after purchase.
Product Categories Worth Knowing
Ready Seal Exterior Wood Stain & Sealer
See It on AmazonWhat We Like
- Best balance of appearance and longevity for most projects
- Wears rather than peels — recoat without stripping
- Real UV protection from pigment load
- Wide colour range and broad availability
What We Don’t Like
- Not as long-lived as solid stain or paint
- Colour choice affects durability, not just looks
- Needs clean, dry, unsealed wood to penetrate
Product Specs
- Type: Penetrating Semi-Transparent Stain
- Rank in this guide: #1
This is the category that suits the widest range of exterior wood projects, and if you are choosing without a specific reason to do otherwise, it is where to start. Enough pigment to block meaningful UV, little enough to leave the grain visible, and penetrating rather than film-forming so it wears evenly and recoats without stripping. Ready Seal, an oil-based penetrating semi-transparent stain, is a widely sold example of the type.
Manufacturers generally state a three-to-five year service interval on vertical surfaces and two to three on horizontal ones, with the difference coming down to water dwell time and foot traffic rather than the product. Southern and western exposures deplete faster than northern.
Within the category, the meaningful specification differences are the UV absorber package, whether a mildewcide is included (essential in humid climates and on any oil-based formulation), and whether the carrier is oil or water. Oil penetrates better on weathered wood; water-based holds colour longer and resists mildew.
Colour choice has a practical dimension beyond taste: darker tones carry more pigment and therefore last longer, at the cost of showing grain less and running hotter in sun.
Thompson's WaterSeal Clear Wood Sealer
See It on AmazonWhat We Like
- No colour change — the wood stays exactly as it is
- Genuine water repellency and reduced checking
- Simple application, no lap marks to worry about
- Inexpensive
What We Don’t Like
- No meaningful UV protection — the wood will still grey
- Annual to biennial reapplication
- Frequently bought expecting colour retention it cannot deliver
Product Specs
- Type: Clear Water Repellent
- Rank in this guide: #2
Clear sealers address exactly one of the two failure mechanisms. They reduce water absorption, which limits the swell-and-shrink cycling that checks and splits wood, and they do essentially nothing about UV because they contain no pigment to block it. Thompson's WaterSeal Clear Wood Sealer is the most widely sold example of the type.
The consequence is predictable and it is the single most common disappointment in exterior wood finishing: the wood greys on schedule despite having been sealed, because greying is UV damage to lignin and the sealer never addressed it. Products marketed with added UV absorbers slow this but do not stop it — organic UV absorbers are themselves degraded by the UV they intercept, which is why they are a one-to-two year proposition.
Where clear sealers make sense: new wood you intend to let grey naturally but want protected from water damage in the meantime, wood species chosen for their natural colour where any pigment would be unwelcome, and short-term protection on lumber awaiting a proper finish.
What We Like
- Longest service life short of paint
- Hides weathering, patches and colour variation
- Wide colour range including custom tinting
What We Don’t Like
- Obscures the wood grain entirely
- Fails by peeling — renewal means scraping
- Poor choice for horizontal deck surfaces
- Traps moisture if applied to damp wood
Product Specs
- Type: Solid Colour Stain
- Rank in this guide: #3
Solid stain is closer to a thin exterior paint than to a stain: it carries enough pigment to obscure wood colour entirely while leaving the surface texture visible. That heavy pigment load is why it lasts five to seven years where a semi-transparent lasts three to five. DEFY Solid Color, a water-based solid stain for decks and fences, is a readily available example.
It is the pragmatic answer for wood that has already weathered badly, for previously painted surfaces, and for anywhere a uniform colour is wanted. It also hides the colour variation that makes patched or mixed-age lumber look mismatched.
The cost is the failure mode. Solid stain forms a film, and films on exterior wood eventually crack and peel rather than wearing away — which means renewal involves scraping and sanding rather than washing and recoating. On horizontal deck surfaces this happens faster and looks worse than anywhere else, which is why solid stains are widely recommended for railings and siding and widely discouraged for deck boards.
Preparation Decides the Outcome
More exterior wood finishes fail from preparation than from product choice, and the steps are not optional.
Clean, and Understand What Cleaning Is For
Grey weathered wood is not dirty — it is a layer of UV-degraded fibres that has lost its bond to the sound wood beneath. Finish applied over it adheres to a layer that is already detaching. A wood cleaner containing sodium percarbonate or oxalic acid removes that degraded layer chemically and restores colour.
Two-part systems pair a cleaner with a brightener. The cleaner, usually alkaline, lifts dirt, mildew and the grey layer; the brightener, usually oxalic or citric acid, neutralises the alkali and restores the wood's natural tone. Skipping the brightener leaves the surface alkaline, which interferes with the adhesion of some finishes.
Do Not Pressure Wash Aggressively
Wood is made of alternating soft spring growth and hard summer growth. A pressure washer erodes the soft bands faster, leaving a raised, furry texture that traps dirt and looks worse than what you started with. If you use one, keep it under 1,200 psi with a wide fan tip, held well back, moving with the grain — and treat it as a rinse for the chemical cleaner rather than the cleaning method itself.
Dry Thoroughly
48 hours of dry weather after cleaning is a minimum, and longer in humidity or on dense wood. Finishes applied to damp wood cannot penetrate, and film-forming products trap the moisture and blister.
Test Absorbency
Sprinkle water on the prepared surface. Absorbed within a minute or two means ready. Beading means either the wood is still wet, an old finish remains, or — on new pressure-treated lumber — the treatment has not dried out yet. In all three cases, finishing now will fail.
Applying It
Conditions: 50–90°F, out of direct hot sun, no rain forecast for 24–48 hours, and low enough humidity that the finish can cure. Finishing a fence at midday in July means the product sets before it penetrates.
Method: Brush, roll or spray, but always back-brush. Spraying alone lays product on the surface; the brush is what works it into the grain and into the checks and end grain where water enters. On a large fence, spray-and-back-brush with two people is far faster than brushing alone and gives the same result.
Coats: Follow the product. Many penetrating stains specify one coat and mean it — a second coat on wood that cannot absorb it leaves a sticky surface film that stays tacky and collects dirt. Where two coats are specified, apply the second while the first is still tacky (wet-on-wet) unless the label says otherwise.
End grain: The ends of boards absorb many times more water than faces, and they are where rot starts. Flood end grain, cut ends, and any joint where two pieces meet.
Maintenance Schedule
The cheapest exterior wood maintenance is recoating slightly early. A penetrating finish that still has some pigment left recoats with a wash and a fresh coat. One that has gone fully grey needs the full clean-and-brighten cycle and 48 hours of drying before you can start.
Check annually with the water test. Beading means the finish is working; absorption means it is time. On a deck, check the traffic lanes and the south-facing edge, which deplete first and tell you the schedule for the rest.
The Short Version
Pick your finish by how much wood grain you are willing to lose, because that is the same axis as how long it lasts. A penetrating semi-transparent stain is the right default for fences, decks and most exterior wood: enough pigment for genuine UV protection, enough transparency to see the wood, and it wears instead of peeling.
Use a clear sealer only if you accept that the wood will grey — it stops water, not sunlight. Use a solid stain on fences, siding and railings where a uniform colour is wanted and peeling is tolerable, and keep it off deck boards.
And spend the effort on preparation. Clean, brighten, dry for 48 hours, test absorbency, then apply in mild conditions with back-brushing and flooded end grain. Preparation is where exterior wood finishes are won or lost.
Frequently Asked Questions
A penetrating semi-transparent stain, for most projects. It carries enough pigment to block the UV that actually greys wood, leaves the grain visible, and penetrates rather than forming a film — so it wears evenly and recoats without stripping. Manufacturers typically state three to five years on vertical surfaces and two to three on horizontal ones. Choose oil-based if the wood is weathered and you want maximum penetration and forgiveness of imperfect prep; choose water-based if mildew is a concern or you want longer colour retention, since modern acrylic resins are more UV-stable than linseed oil. Darker colours carry more pigment and last longer than lighter ones, which is a durability decision as much as an aesthetic one.
Because you almost certainly used a clear sealer, and greying is UV damage rather than water damage. Ultraviolet light breaks down lignin, the polymer binding wood fibres together, and the degraded surface layer turns silver-grey. Clear sealers contain no pigment, and pigment is what blocks UV — so a clear product reduces water absorption and does essentially nothing about the mechanism that causes greying. Products advertising added UV absorbers slow it but cannot stop it, because organic UV absorbers are themselves consumed by the light they intercept, which is why they are a one-to-two year proposition. If you want the wood to keep its colour, you need pigment: a semi-transparent stain at minimum.
In exterior wood products the terms overlap heavily and the useful distinction is pigment, not the name on the tin. A sealer's job is water repellency; a stain's job is colour plus water repellency. Most products marketed as stains are also sealers, and many products called sealers carry some pigment. What matters when choosing: how much pigment (which determines both UV protection and how much grain you see), whether it penetrates or forms a film (which determines whether it wears away or peels, and therefore how you recoat), and whether the carrier is oil or water. Products sold as stain-and-sealer-in-one are simply pigmented penetrating finishes, which is the category most exterior wood should get anyway.
A semi-transparent stain in a tone close to the natural wood. Both species contain natural extractives that give them rot resistance and their characteristic colour, and both grey rapidly under UV without a pigmented finish — so a clear sealer will leave you with a silver fence within a season or two despite having sealed it. A fence is vertical, sheds water fast, and takes no traffic, which makes UV the dominant failure mode and argues for pigment. Practically: fences are large, so cost per square foot matters, and spraying with back-brushing is far faster than brushing alone. Expect three to five years before recoating, and check the south and west-facing sections first since they deplete soonest.
Usually not — new pressure-treated lumber is often too wet to accept a finish. The treatment process saturates the timber, and a finish applied before it dries traps that moisture, preventing penetration and causing film-forming products to blister. Test with the water-sprinkle method: if water beads on the surface, the wood is still too wet; if it soaks in within a minute or two, it is ready. Depending on the lumber, the climate and the time of year, that can be anywhere from a few weeks to several months after purchase. In the meantime the treatment itself protects against rot and insects, so there is no urgency — the finish is for UV protection and appearance, and applying it early achieves neither.
Only lightly, and only as a rinse. Wood is made of alternating soft spring growth and hard summer growth, and a pressure washer erodes the soft bands faster than the hard ones, leaving a raised, furry surface that traps dirt and looks worse than what you started with. If you use one, keep it under 1,200 psi with a wide fan tip, held well back and moving with the grain. The actual cleaning should be chemical: a wood cleaner containing sodium percarbonate or oxalic acid dissolves the UV-degraded grey layer that finish would otherwise bond to, followed by a brightener to neutralise the alkalinity and restore tone. Then allow 48 hours of dry weather before applying anything.
Follow the product, and with penetrating stains resist the urge to add more. Many specify a single coat and mean it: the wood absorbs what it can hold, and anything beyond that sits on the surface as a film that stays tacky, collects dirt and eventually has to be cleaned off. Where two coats are specified, they are usually applied wet-on-wet — the second going on while the first is still tacky — rather than after drying. Whatever the coat count, flood the end grain, cut ends and joints, because end grain absorbs many times more water than face grain and is where rot begins. And always back-brush after spraying or rolling, since that is what works the product into the grain rather than leaving it on top.
If the wood lives within a few hundred yards of salt water, yes. Marine formulations carry substantially heavier UV absorber packages, because a boat sits in unshaded sun over a reflective surface, and they are tested against salt, which crystallises inside a finish, stresses it mechanically and draws moisture. They are also formulated to stay flexible as wood moves with humidity, which matters more in a marine environment than inland. Away from the coast the premium is harder to justify — a good semi-transparent exterior stain will perform comparably on a garden bench and costs less. The exception is any piece that gets soaked regularly, such as dock furniture or a poolside bench, where the extra flexibility and UV package earn their keep.