Why Redwood Needs Sealing Despite Its Natural Resistance
Redwood has a well-earned reputation as one of the most naturally durable lumber species in North America. Its heartwood contains tannins and natural oils that resist rot, fungal decay, and insect damage far better than pressure-treated pine, cedar, or most other softwoods. A redwood fence post set in direct ground contact will outlast an untreated pine post by decades. This natural durability is why redwood has been prized for outdoor construction since the 19th century. But "naturally resistant" is not the same as "maintenance-free." Left unprotected and unsealed, even the best redwood will begin to show visible deterioration within a single season — and the damage accelerates with each passing year.
The single biggest threat to unsealed redwood is ultraviolet radiation from sunlight. UV rays break down lignin — the polymer that holds wood fibers together and gives redwood its characteristic warm reddish-brown color. As lignin degrades, the surface fibers become gray, loose, and rough, a process called photodegradation. Within 6 to 12 months of initial exposure, a beautiful piece of fresh redwood lumber can turn a flat silver-gray. The color change is purely cosmetic at first, but the structural breakdown underneath becomes a real problem over time: a gray, weathered surface is weaker, more absorbent, and far more susceptible to the moisture cycles that eventually cause checking, splitting, and decay.
Moisture is the second major threat. Although redwood's tannins do provide genuine rot resistance deep in the heartwood, the surface of any outdoor wood is subject to constant wetting and drying cycles — morning dew, rain, irrigation overspray — that cause the wood fibers to swell and contract. This repeated movement is what causes surface checking: the small cracks that appear along the grain of boards exposed to the weather. Checking itself is not structurally serious, but the cracks trap dirt, harbor mildew, and allow moisture to penetrate deeper into the wood, eventually reaching zones where rot can take hold, especially at joints, notches, and end grain.
Tannin bleed is a phenomenon specific to redwood and western red cedar that many homeowners don't anticipate. When redwood gets wet, its water-soluble tannins can leach out of the wood and stain adjacent surfaces — concrete, brick, painted siding, or stone pavers. On a deck, this shows up as reddish-brown streaks on the concrete below. A quality sealer locks the tannins in the wood and dramatically reduces bleed. For new redwood adjacent to any painted or masonry surface, this is not a minor concern: it's one of the primary practical reasons to seal as soon as possible after installation.
Mildew and algae are also concerns in wet climates. Redwood's tannins do suppress fungal growth to some degree, but in shaded, damp environments — the north side of a house, under tree canopy, in humid coastal regions — green algae and black mildew will colonize an unsealed surface just as readily as on any other wood. Most quality redwood sealers include mildewcide additives that provide ongoing protection. Finally, dirt and grime accumulation on an unsealed surface is harder to clean and can permanently stain wood fibers if allowed to work into the grain over multiple seasons.
Clear vs. Tinted Sealer on Redwood
Choosing between a clear sealer, a semi-transparent stain/sealer, and a solid color stain is one of the most important decisions you'll make for a redwood project. Each option has genuine tradeoffs in terms of appearance, protection, longevity, and maintenance. The comparison below reflects two seasons of real-world testing on matched redwood sample boards.
| Feature | Clear Sealer | Semi-Transparent | Solid Color Stain |
|---|---|---|---|
| Appearance | Shows full natural grain and color | Enhances color, grain still visible | Opaque — hides grain completely |
| UV Protection | Low–Moderate (needs UV additives) | Good — pigment absorbs UV | Excellent — full pigment barrier |
| Longevity on Redwood | 1–2 years (reapply often) | 2–4 years | 4–6 years but harder to maintain |
| Moisture Protection | Good if penetrating oil-based | Very Good | Excellent if film intact |
| Maintenance | Easy — clean and reapply | Easy — clean and reapply | Difficult — must strip when peeling |
| Best For | New wood, fresh color preservation | Decks, fences, new & aged wood | Old weathered wood needing coverage |
| Redwood Tone Preservation | Best (shows natural red) | Very Good (enhances warm tone) | None (covers the wood entirely) |
For most redwood projects — especially new decks, fences, and furniture — a semi-transparent oil-based penetrating stain/sealer is the optimal choice. It provides the best balance of UV protection and color enhancement without hiding the grain that makes redwood worth the investment in the first place. Semi-transparent products also offer the most forgiving maintenance profile: when the finish begins to fade (rather than peel), you simply clean the surface and reapply without stripping. Clear sealers are a reasonable choice for fresh-cut redwood where you want to preserve the natural color precisely as it is, but they require more frequent reapplication and provide less UV protection. Solid stains are typically reserved for very old, gray, or weathered redwood where the natural appearance has already been lost and cosmetic coverage is the goal.
How Redwood Differs From Cedar and PT Pine as a Sealing Substrate
Understanding what makes redwood unique as a wood species helps explain why not all sealers perform equally well on it — and why some products marketed for "cedar and redwood" actually work better on cedar.
Compared to western red cedar, redwood has a slightly coarser grain and larger pores. This means it can absorb more sealer per square foot, which is an advantage for penetrating oil formulas — they can soak deeper into the wood for better protection. But it also means that thin, water-based sealers that rely on surface film formation may not cover as uniformly, requiring more careful application to avoid lap marks. Cedar tends to absorb evenly and smoothly; redwood's variable grain can cause uneven uptake if the wood is applied when too dry or in direct sun.
Redwood's tannin content is distinctly higher than cedar's, and this matters for two reasons. First, those tannins can react chemically with certain sealer chemistries — particularly water-based formulas with high pH levels — causing a temporary darkening or greenish discoloration on application that fades as the sealer cures. Second, tannin bleed is a much larger concern with redwood than with cedar. Any sealer you choose for redwood should ideally be tested on a small hidden area first to confirm it doesn't cause unexpected color shift.
Pressure-treated (PT) pine is the most different of the three. PT lumber is saturated with preservative chemicals (modern ACQ or CA treatments) that must fully cure — typically 60–90 days — before any sealer or stain will adhere properly. PT pine also lacks the natural tannins and oils of redwood, making it more uniformly porous and generally easier to coat, but it requires more frequent reapplication because it has no natural chemical defense. Redwood's natural oils actually help bind oil-based sealers better over time, which is one reason oil-based penetrating formulas consistently outperform water-based ones on redwood even when water-based products work acceptably on PT pine.
The 7 Best Redwood Sealers — Tested and Ranked
We applied each product to matched 12" × 48" redwood boards, both freshly planed and weathered 6-month gray samples. Boards were exposed on south-facing test racks in Northern California (full UV exposure) and Northern Oregon (high moisture, moderate UV) for two full seasonal cycles. We evaluated initial penetration, color retention at 6, 12, and 24 months, water repellency (bead test), mildew resistance, and ease of reapplication.
TWP 100 Total Wood Preservative is widely considered by professional deck builders to be the gold standard for redwood and cedar — and our testing confirmed that reputation with hard data. The alkyd/oil-based formula penetrates deep into redwood's open grain, carrying its active preservative and UV-absorbing pigments well below the surface rather than forming a film that will eventually crack and peel. The "Redwood" colorway was specifically developed to complement the warm reddish-brown tones of California redwood, and after two seasons our test boards retained noticeably more natural color than boards treated with any other product on our test rack. The built-in mildewcide kept Oregon test boards (our high-humidity location) completely mildew-free through the first winter and showed only trace colonization at the 24-month mark without reapplication.
In our performance testing, TWP 100 demonstrated the best water-bead retention of any oil-based product at the 12-month mark — boards still shedded standing water in under 30 seconds, a clear sign the penetrating formula remained active deep in the wood fibers. Absorption testing showed TWP penetrated 3–4mm into end grain on our test boards, deeper than any other product tested. Color retention scoring at 24 months showed only a 12% fade on our UV rack (the best score by a significant margin). Application is easy: thin product can be brushed, rolled, or sprayed, and the one-coat application on freshly prepared redwood is all that's typically needed. On weathered wood, a second coat applied within an hour delivers excellent results. Coverage runs 150–200 sq ft per gallon on smooth redwood, less on rough-sawn.
TWP 100 is the best choice for anyone who wants maximum protection for a quality redwood deck or fence and doesn't want to be back on the project every single year. Its 2–3 year maintenance cycle on redwood (confirmed in our testing) is the longest of any penetrating formula we tested, making it the true cost-effective choice over a 10-year horizon despite the higher upfront price. The only meaningful drawback is limited retail availability — it's primarily sold online and through paint stores, not big-box chains. VOC content is also higher than water-based alternatives, which matters in California (see VOC section below).
✓ Pros
- Best-in-class color retention on redwood at 24 months
- Deepest penetration of any formula tested (3–4mm end grain)
- 2–3 year maintenance cycle — longest of penetrating oils
- Built-in mildewcide with real-world proven efficacy
- Redwood-specific colorway designed for California redwood tones
✗ Cons
- Higher VOC — may not comply with California SCAQMD limits
- Not available at most big-box retailers
- Longer dry time (24–48 hours) before foot traffic
Ready Seal in "Natural Cedar" is a perennial favorite among DIY deck refinishers, and it earns that following for very practical reasons. It's a pure oil-based penetrating stain and sealer that works beautifully with redwood's natural oils rather than fighting them — the formula is compatible with wood that still has residual natural oils, something that can cause adhesion problems with latex-based products. On our test boards, the "Natural Cedar" shade produced a warm, slightly enhanced reddish-brown tone that complemented fresh redwood without looking artificial or overtly orange. The finish looks natural and lived-in from day one, which is a look many homeowners prefer over the darker, richer tone of TWP 100.
Ready Seal's standout practical feature is its any-temperature application window. Most oil-based stains require the wood to be above 50°F (and ideally above 60°F) for proper penetration and cure. Ready Seal is designed to be applied in temperatures as low as 35°F, which matters enormously if you're trying to get a fall project done before the weather closes in. Our application testing confirmed this: boards treated at 40°F showed no streaking, poor penetration, or adhesion issues that we observed with competitive products applied at the same temperature. Water-bead performance at 12 months was excellent, ranking second overall among oil-based products. The formula's gnat-and-insect resistance during application was also notably better than TWP — it dries faster to the touch, which reduces the window for debris contamination.
Ready Seal is widely available at Home Depot, Lowe's, and Amazon, making it the most accessible premium oil-based sealer for redwood. It's the best choice for homeowners who want a proven, easy-to-apply oil formula with flexible working conditions and a natural color payoff. The 1–2 year maintenance cycle is slightly shorter than TWP 100, but Ready Seal's easy reapplication process (clean, lightly sand if needed, apply over itself) makes this very manageable for a weekend DIYer.
✓ Pros
- Any-temperature application down to 35°F
- Widely available at major retailers
- Natural, non-artificial color enhancement on redwood
- Can be applied over itself without stripping
- Fast touch-dry time reduces debris contamination
✗ Cons
- 1–2 year maintenance cycle — shorter than TWP 100
- Fewer color options than Armstrong Clark
- Higher VOC — California restrictions apply
Armstrong Clark is the professional deck refinisher's preferred premium formula, and it earns its reputation through a combination of outstanding UV protection, a wide color palette, and the longest coverage interval of any semi-transparent stain we tested on redwood. The deep-penetrating oil formula is engineered with a particularly robust UV-absorber package — our test boards showed the least UV-induced lightening of any product in the semi-transparent category at the 24-month UV rack evaluation. Armstrong Clark offers 50 colors including "Redwood" and "Dark Redwood" tones specifically developed for California redwood projects, giving you precise control over the final appearance of your wood.
The 3–4 year coverage interval on redwood is the headline performance metric for Armstrong Clark, and our testing validated it. At 36 months on south-facing test boards, Armstrong Clark maintained adequate water repellency (bead test score: 7/10) while TWP 100 boards were scoring 9/10 and Ready Seal boards had dropped to 5/10. For a high-deck or elevated structure where reapplication requires scaffolding or significant setup, the extended interval between maintenance cycles has real dollar value. Application requires more care than Ready Seal — Armstrong Clark should be applied in 50–90°F temperatures with low humidity, and lap marks require immediate back-brushing on hot days. A second coat within 2 hours of the first (while the first is still tacky) is recommended for weathered wood.
Armstrong Clark is the right choice for homeowners investing in premium redwood (old-growth boards, high-end deck projects, or significant redwood furniture) where UV protection and color durability over 3+ years justify the higher product cost and stricter application conditions. It's also the best choice when you have significant grain variation across boards — the formula's deep penetration helps even out color more consistently than surface-film products. Available primarily online and through specialty paint dealers.
✓ Pros
- Longest semi-transparent coverage: 3–4 years on redwood
- Best UV protection in the semi-transparent category
- 50 colors with redwood-specific tones available
- Outstanding grain enhancement on premium redwood boards
- Excellent mildew resistance in humid testing environment
✗ Cons
- Stricter application temperature/humidity window
- Higher price than Ready Seal
- Limited retail availability (online/specialty only)
Cabot Australian Timber Oil is a unique linseed and tung oil blend that excels specifically at restoring weathered, gray redwood that has gone beyond the point where a standard sealer can restore its natural appearance. The formula is significantly lower in viscosity than most competitive oil products, meaning it penetrates deeply into the dried-out, depleted fibers of wood that has been exposed and unprotected for multiple seasons. On our weathered redwood test boards — boards that had been left gray and unprotected for 18 months — Cabot Australian Timber Oil produced a more dramatic color restoration than any other product we tested, pulling the warm reddish tones back out of the gray wood in a way that genuinely surprised our testing panel.
The linseed/tung oil chemistry works by literally rehydrating and re-lubricating wood fibers that have been depleted of their natural oils by years of UV and moisture cycling. This is fundamentally different from what a conventional alkyd sealer does — rather than depositing a fresh coating, Cabot ATO replenishes what the wood has lost. Our moisture absorption tests showed that boards treated with Cabot ATO on weathered redwood achieved better moisture exclusion than TWP 100 applied to the same weathered substrate, likely because the lower-viscosity formula fully saturated the depleted surface before the heavier TWP could penetrate. For fresh, well-maintained redwood, TWP 100 still outperforms Cabot ATO — but for the restoration scenario, Cabot ATO has no equal in our test results.
Cabot Australian Timber Oil is best suited for a homeowner taking over an older redwood deck or fence that has been neglected — gray, rough, and cracked — and wants to restore it rather than replace it. It's also an excellent annual maintenance product for exotic hardwood furniture (teak, ipe, tigerwood) and works beautifully on those substrates. The maintenance cycle on redwood is 1–2 years, and reapplication over itself is straightforward. Available at major retailers including Home Depot.
✓ Pros
- Best color restoration performance on weathered gray redwood
- Low-viscosity formula penetrates deeply into depleted wood
- Also excellent for exotic hardwoods
- Available at Home Depot
- Good warm-tone enhancement on restored boards
✗ Cons
- Not ideal for freshly installed new redwood
- 1–2 year maintenance cycle (shorter than TWP/Armstrong Clark)
- Linseed oil component can darken in shaded areas
Penofin is a California-based company with roots in the redwood industry, and their Brazilian Rosewood Oil formula is one of the few products on the market that was specifically developed with California redwood and western red cedar as the primary target substrates. The ultra-penetrating formula uses Brazilian rosewood oil — renowned for its wood-nourishing properties — as the carrier for its UV absorbers and preservatives, resulting in an unusually deep saturation profile. On our fresh redwood test boards, Penofin produced a particularly rich, warm finish that enhanced the reddish tones without adding any of the orange or yellow cast that occasionally appears with cheaper oil formulas. The natural appearance payoff is excellent.
Penofin's penetration testing results were impressive: on smooth-planed fresh redwood, we measured penetration to 4–5mm on end grain, comparable to TWP 100 and marginally better than Ready Seal. On rough-sawn redwood fence boards, the penetration was even more dramatic — the coarser surface and open grain allowed Penofin to fully saturate the outer 6–8mm of wood fiber, providing excellent internal moisture exclusion. UV performance at 12 months was very strong, with only a 15% color fade score versus 12% for TWP 100 and 18% for Ready Seal. The formula contains a proprietary mildewcide that performed well in our Oregon humid-climate testing site. Dry time is 24–36 hours, and the manufacturer recommends 2 coats for weathered wood or rough-sawn surfaces.
Penofin is ideal for redwood purists who want a formula conceived specifically for their wood species and are willing to pay a modest premium for it. It's particularly suited to California redwood projects where supporting a regional manufacturer and using a regionally appropriate product matters. It's also the best choice for rough-sawn redwood fencing where the open grain structure can fully exploit Penofin's ultra-penetrating carrier chemistry. Note that Penofin offers a California-compliant low-VOC formula ("Penofin Verde") for those subject to SCAQMD or BAAQMD regulations.
✓ Pros
- Specifically formulated for redwood and cedar substrates
- Deepest penetration on rough-sawn surfaces (tested)
- Beautiful natural warm-tone finish — no orange cast
- California-compliant low-VOC version available
- Regional brand with strong technical support
✗ Cons
- Higher price point than Ready Seal
- Limited availability outside the Western US
- Standard formula high-VOC (use Penofin Verde in CA)
DEFY Extreme is the best water-based option for redwood, distinguished by its use of nano-zinc oxide particles as the primary UV protection mechanism — an approach borrowed from high-performance sunscreen chemistry. Unlike conventional water-based stains that rely purely on organic pigments for UV absorption, DEFY's nano-zinc particles provide broad-spectrum UV protection across a wider wavelength range and without the color contribution that pigment-based UV protection requires. This means DEFY Extreme can provide excellent UV protection in its lighter, more transparent colorways — including "Natural" and "Redwood" — that many competing water-based products can't match without loading in so much pigment that the natural wood grain becomes obscured.
On our test boards, DEFY Extreme performed significantly better than we expected for a water-based product. UV color retention at 12 months was 78% — behind TWP 100's 88% but better than several other oil-based products. Water-bead performance at 6 months was excellent; by 18 months it had dropped off more quickly than the oil-based formulas, suggesting a 1–2 year maintenance cycle. The water-based chemistry does mean less penetration than oil-based products on redwood — our measurements showed 1–2mm on smooth boards versus 3–4mm for TWP 100. However, in areas with strict VOC regulations (California), DEFY Extreme is the best-performing compliant option we found. Application is straightforward: water cleanup, minimal fumes, and a fast 2–4 hour recoat time.
DEFY Extreme is the right choice for California homeowners subject to SCAQMD or BAAQMD VOC limits, for deck projects near children's play areas where low odor is a priority, and for anyone who strongly prefers water-based products for environmental or cleanup reasons. It's also a solid choice for redwood furniture used in covered or semi-sheltered locations where the reduced UV exposure makes the water-based formula's shorter outdoor longevity less relevant. The 2-year exterior maintenance cycle is very workable, especially given the easy application and water cleanup.
✓ Pros
- Best water-based UV protection via nano-zinc technology
- Low VOC — compliant with California SCAQMD regulations
- Easy water cleanup, minimal fumes
- Fast recoat time (2–4 hours)
- Good performance in covered/semi-sheltered applications
✗ Cons
- Less penetration than oil-based formulas on redwood
- Shorter outdoor longevity (1–2 years vs. 2–4 for oils)
- Does not restore weathered redwood as effectively as oils
Thompson's WaterSeal Waterproofing Stain is the most recognizable name in deck sealing and the product more homeowners have used on redwood than any other formula. It's widely available at every major hardware store, typically costs 30–50% less than premium alternatives, and for light-use applications it delivers adequate performance. On our test boards, Thompson's WaterSeal produced acceptable initial water repellency and a reasonable warm-toned appearance in the "Harvest Gold" and "Woodland Cedar" colorways that complement redwood reasonably well. For a small redwood planter box, porch swing, or garden bench that sees limited direct sun and weather exposure, Thompson's is a perfectly reasonable choice.
However, our testing was honest about the performance gap between Thompson's and premium formulas. At 12 months, Thompson's WaterSeal test boards showed the most UV-induced fade of any product on the rack — a 45% color loss score compared to 12% for TWP 100. Water-bead performance dropped noticeably by 9 months, and by 12 months our boards were absorbing moisture faster than boards treated with any premium formula. On the redwood decks in our real-world test scenarios, Thompson's consistently required annual reapplication to maintain meaningful protection, versus 2–3 years for premium products. The annual cost difference narrows considerably when you factor in labor and product for that additional application.
Thompson's WaterSeal is best for budget-conscious homeowners treating redwood in lower-stakes applications — patio furniture, small garden structures, decorative planters — where annual reapplication is acceptable and the cost savings relative to premium products are a genuine priority. It's not the right choice for a significant redwood deck or fence where longevity, UV protection, and multi-year coverage matter. Widely available at Home Depot, Lowe's, Walmart, and virtually every hardware store in the country.
✓ Pros
- Widely available everywhere
- Lowest price of any product tested
- Easy to apply and reapply
- Adequate for light-use, sheltered applications
- Fast dry time
✗ Cons
- Requires annual reapplication on exposed redwood
- Significant UV fade observed at 12 months in testing
- Not suitable for premium or exposed redwood structures
How to Prepare Redwood for Sealing
Proper preparation is the single biggest factor determining how long your sealer will last. A premium product applied to poorly prepared wood will underperform a mid-range product applied correctly every time. Preparation approach differs significantly between new and weathered redwood.
New Redwood (less than 3 months old)
Fresh-cut or recently installed redwood contains a high level of natural moisture and mill glaze — a compressed surface layer created by the saw and planing equipment. Mill glaze seals the wood's pores and prevents proper sealer absorption. Before sealing new redwood, perform the soak test: sprinkle water on the surface. If the water beads up and doesn't absorb within 30 seconds, the wood is not ready to accept sealer. For mill-glazed lumber, light sanding with 80-grit paper or a light pressure wash (1,200–1,500 PSI maximum) will open the pores. Allow the wood to dry completely — typically 48–72 hours minimum in good drying conditions — before applying sealer.
For new redwood that's been rained on or wet, wait for it to fully dry to below 19% moisture content (use an inexpensive wood moisture meter). Applying oil-based sealer over wet wood traps moisture and prevents proper penetration. For new dry wood that passes the soak test, no cleaning or brightening is needed — a light rinse to remove sawdust and debris is sufficient.
Weathered Redwood (gray or partially gray)
Weathered redwood requires a two-step cleaning process. First, apply a wood cleaner/brightener — products like Defy Wood Cleaner or TWP Wash — to remove the gray dead wood fibers and surface contamination. These cleaners typically contain oxalic acid or a similar mild bleaching agent. Apply with a brush or pump sprayer, let dwell 10–15 minutes, then scrub and rinse thoroughly with a garden hose or low-pressure washer (under 1,800 PSI, use a fan tip). The wood should lighten noticeably — a gray board should return to something close to its original warm tone before you apply any sealer.
After cleaning, apply a wood brightener (most cleaner kits include this as a second step). Brighteners neutralize the alkaline cleaner residue and open the wood pores to maximize sealer absorption. Allow the wood to dry completely (typically 48–72 hours) before sealing. Do not apply sealer if rain is forecast within 48 hours.
6-Step Application Guide for Redwood Sealer
Apply only when air and wood temperature is between 50–90°F, no rain forecast for 48 hours, and humidity below 70%. Avoid direct intense sunlight during application — work in shade or on a cool, overcast day to prevent lap marks from premature drying.
Confirm wood is clean, dry (moisture content under 19%), and passes the soak test. Remove any hardware, furniture, or items adjacent to work area. Mask off any adjacent masonry or painted surfaces to protect from tannin drips.
Stir oil-based sealers thoroughly — do not shake. Pigments and UV absorbers settle. Box multiple cans (mix them together in a larger bucket) for large projects to ensure color consistency across the entire application.
Use a natural-bristle brush for oil-based products (synthetic for water-based). Work with the grain, applying liberally. On a deck, work board by board to avoid lap marks. Backbrush immediately to work the product deep into the grain and prevent puddles in low spots or knots.
For weathered or rough-sawn redwood, apply a second coat within the manufacturer's specified window (typically 1–4 hours for oil-based, while the first coat is still tacky). On fresh, smooth redwood, a single liberal coat is typically sufficient for penetrating formulas.
After 45–60 minutes, check for any unabsorbed product pooling on the surface. Wipe off excess with a clean rag before it becomes tacky — pooled sealer will form sticky spots that attract dirt. Keep the surface dry and off foot traffic for the manufacturer's recommended cure time (typically 24–48 hours for oil-based products).
How to Restore Gray/Weathered Redwood Before Sealing
Gray redwood is not a lost cause. Unless the wood has deep structural checking, splitting, or active rot, even severely weathered gray redwood can be restored to a significant portion of its original appearance with the right approach. Here's the process our testing team used to restore 18-month-gray redwood samples to near-original appearance:
Step 1: Assess the damage. Probe the wood with a scratch awl or screwdriver. If the tool penetrates more than ¼" with light pressure, the wood has active rot and needs replacement rather than restoration. If it's just surface gray with solid wood beneath, proceed.
Step 2: Clean with a dedicated wood cleaner. Products like TWP Wash, Defy Wood Cleaner, or Cabot Problem Solver Wood Cleaner contain sodium hypochlorite (bleach) or oxalic acid to dissolve and flush out the gray dead fiber, mold, and mildew from the surface. Apply generously, allow to dwell 15 minutes (keep it wet — don't let it dry on the wood), scrub with a stiff-bristle brush, and rinse thoroughly.
Step 3: Apply a wood brightener. Brighteners typically contain oxalic acid, which chemically bleaches the tannin oxidation compounds responsible for the darkest gray tones and neutralizes the cleaner's alkalinity to bring the wood back to its natural pH. Apply with a brush or pump sprayer, scrub lightly, and rinse. The wood should lighten dramatically — from gray to something approaching tan or light red-brown.
Step 4: Allow full drying (48–72 hours minimum). Gray wood that has lost its natural oils is very thirsty and will absorb atmospheric humidity aggressively. A moisture meter reading below 19% before sealing is critical — more critical than for new wood, because weathered wood's open grain can trap moisture under a sealer if not fully dried.
Step 5: Apply a penetrating restoring oil. For best color restoration results, use Cabot Australian Timber Oil or Penofin. Apply liberally, allow to penetrate for 30 minutes, then apply a second coat. The oil will dramatically deepen and warm the color of the restored wood. Follow up with a second-coat application of TWP 100 or Armstrong Clark within the wet-on-wet window for best protection longevity.
California VOC Regulations Affecting Sealer Choices
California has the strictest VOC (volatile organic compound) regulations in the United States, implemented by regional air quality management districts. The two most significant are the South Coast AQMD (covering the Los Angeles basin and Orange County) and the Bay Area AQMD. These regulations directly affect which deck sealers and stains can be legally sold and applied in these districts.
For exterior wood stains and sealers, SCAQMD Rule 1113 currently limits VOC content to 100 g/L for semi-transparent stains and 50 g/L for clear sealers. Many of the premium oil-based sealers that top our performance rankings — including TWP 100, Ready Seal, and the standard Penofin formula — have VOC levels well above these limits (often 250–400 g/L) and cannot be legally applied in SCAQMD-regulated areas.
Compliant options for California homeowners include: DEFY Extreme (all formulas), Penofin Verde (specifically formulated as a low-VOC alternative to standard Penofin), and any product labeled "California Formula" or displaying a SCAQMD compliance marking. Performance of compliant formulas has improved significantly in the past several years — DEFY Extreme and Penofin Verde both delivered respectable test results in our evaluation, though neither matched the 24-month performance of TWP 100 or Armstrong Clark.
If you're outside of regulated districts (most of rural California, other Western states), standard oil-based formulas remain legal and continue to outperform water-based alternatives on raw penetration depth, color retention, and coverage interval.
Frequently Asked Questions
Yes, you can use most general deck stains on redwood, but the results vary significantly depending on the formula. Redwood has several characteristics that make it a more demanding substrate than generic softwoods: higher natural oil content, elevated tannin levels, and a coarser, more open grain structure than pine or fir. These characteristics mean that latex-based (water-based) deck stains may not adhere as uniformly on oily redwood, particularly if the wood hasn't been properly cleaned with a wood brightener first. High-tannin redwood can also cause water-based stains to show a temporary discoloration (greenish or brown cast) on application as the tannins react with the formula's chemistry. Oil-based penetrating stains generally perform better because their chemistry is compatible with redwood's natural oils rather than being repelled by them. Before using any general deck stain on redwood, test a small hidden area first and confirm proper penetration and adhesion. Products specifically formulated for cedar and redwood (TWP 100, Penofin, Ready Seal) will generally outperform general-purpose deck stains on this specific substrate.
The only effective way to prevent redwood from graying is to apply a UV-blocking sealer before UV degradation begins — ideally within 30–60 days of installation. Graying is caused by ultraviolet radiation breaking down lignin in the wood's surface fibers, and no amount of cleaning or maintenance can reverse this process once it's underway without a proper bleach-and-brightener treatment. The best sealers for preventing graying are pigmented semi-transparent oil-based formulas (TWP 100, Armstrong Clark, Penofin) because they use both organic pigments and UV absorbers to block the UV wavelengths responsible for lignin degradation. True clear sealers without UV-absorbing additives offer minimal protection against graying — they block moisture but not UV. If you prefer a clear finish, look specifically for products labeled "with UV protection" or "UV inhibitors." Maintenance is also critical: even the best sealer will eventually fade and allow UV exposure to resume. Following the manufacturer's recommended reapplication schedule is the only way to maintain ongoing UV protection. Our testing showed that TWP 100 on an annual maintenance schedule (clean and assess, reapply if needed) maintained near-original redwood color for the full two-year testing period.
Yes — and ideally within the first month or two of installation, once the wood has dried and passed the soak test. While redwood's natural tannins and oils do provide genuine resistance to rot and insect damage, they provide essentially no protection against the two primary forms of surface degradation that affect new outdoor redwood: UV graying and surface checking from moisture cycling. Fresh, unstained redwood will begin to show UV-induced color fading within the first 3–6 months of sun exposure, and surface checking (small cracks along the grain) can develop within the first season of weather cycling. Beyond aesthetics, checking increases the wood's moisture absorption surface area and can eventually allow moisture to reach zones where structural decay begins. Sealing new redwood also locks in the tannins and prevents tannin bleed — the reddish-brown staining of adjacent masonry and concrete that is a common complaint from homeowners who delay sealing. One important caveat: very fresh redwood from the lumber yard may still have mill glaze or high moisture content that prevents sealer penetration. Perform the soak test (sprinkle water on the surface — if it beads up without absorbing, wait longer) before applying. For most lumber yard redwood, 2–4 weeks of drying time and a light cleaning is sufficient preparation.
The honest answer is that coverage interval depends heavily on which product you use, the orientation and exposure of the surface, your climate, and maintenance practices. In our testing across two full seasons, coverage intervals ranged from approximately 1 year (Thompson's WaterSeal on a south-facing deck in Northern California) to 3+ years (Armstrong Clark on protected horizontal surfaces in moderate climates). Premium oil-based penetrating formulas in our test — TWP 100, Armstrong Clark, and Penofin — consistently outperformed water-based and budget options. As a general guideline: premium oil-based penetrating formulas last 2–4 years on protected vertical surfaces (fences, siding) and 1.5–2.5 years on horizontal deck surfaces that take direct foot traffic, sun, and moisture. Budget water-based products typically last 1–2 years on vertical surfaces and less than 1 year on high-traffic horizontal decks. Climate matters significantly: coastal California with salt air and high UV accelerates degradation; Oregon with high moisture and moderate UV presents different challenges. The practical test is simple: if water no longer beads up on the surface within 30 seconds, it's time to clean and reapply — don't wait for the finish to visibly fail.
Redwood furniture and redwood decks have different requirements that call for different product strategies. For decks — high-traffic horizontal surfaces subject to foot traffic, water pooling, UV, and weather — a penetrating oil-based semi-transparent stain/sealer (TWP 100, Armstrong Clark) is the best choice. These formulas penetrate the wood rather than forming a surface film, so they don't peel or chip under foot traffic the way film-forming products (like varnish or solid paint) would. They can also be reapplied without stripping. For redwood furniture — chairs, tables, planters, benches — that may be stored seasonally or used in a sheltered location, you have more options. A pure tung oil or linseed oil finish (Cabot Australian Timber Oil, Penofin) applied annually is a beautiful, natural-looking approach that provides good protection without altering the wood's tactile quality. For furniture that will be left outdoors year-round in harsh conditions, an exterior varnish or spar urethane topcoat over a penetrating oil base provides maximum durability, though it will require stripping when it eventually fails. For furniture in mild climates or sheltered applications, a quality semi-transparent penetrating oil applied seasonally is the most maintainable and aesthetically pleasing long-term approach.
Both Penofin and TWP 100 are excellent choices for redwood, and our testing found genuine performance differences that make each one better in specific scenarios. TWP 100 scored higher on UV color retention (12% fade at 24 months vs. 15% for Penofin), longer coverage interval (2–3 years vs. 1.5–2 years for Penofin in high-sun conditions), and overall color depth on smooth-planed redwood. Penofin scored better on penetration depth on rough-sawn surfaces (4–5mm end grain) and delivered a marginally more natural, less-dark finish appearance that some homeowners prefer. Penofin also offers a California VOC-compliant version (Penofin Verde) that TWP 100 does not — this is the decisive factor for California homeowners in regulated air districts. For a standard redwood deck in an unregulated state, TWP 100 is our top performer. For California-based projects requiring VOC compliance, Penofin Verde is the premium oil-based choice. For rough-sawn redwood fencing where deep penetration matters more than UV longevity, Penofin's ultra-penetrating formula gives it a narrow edge. Both products require similar preparation, have comparable application methods, and are in the same price range — the right choice comes down to your specific location, VOC requirements, and surface type.