Finishing Options
Thermowood is sold unfinished. Left outside, it weathers from its rich Nordic brown to a warm silver-grey patina. Some projects want to lock in that silver look from day one. Others want to preserve the original brown for as long as possible. We offer both — applied in-house at our Greenville facility before your boards ship.
Fresh brown · Naturally aged silver · Valhalla pre-silvered. Labeled, same profile, even lighting.
How Thermowood weathers naturally
Fresh off the mill, Thermowood has a deep, uniform caramel-brown tone. Left untreated in full sun, that brown begins shifting toward silver-grey within the first six to twelve months. The transition takes one to three years to complete, and during that time the weathering is rarely even — south and west elevations grey faster than north and east, which can produce a streaked or splotchy appearance across a single facade.
Single building, different elevations at different silvering stages. The problem Valhalla solves.
By year two or three, most exposures settle into a consistent warm silver that many clients come to prefer over the original brown. Critically, this weathering is cosmetic only. The thermal modification process permanently alters the wood's cell structure. Dimensional stability, rot resistance, and Class 1 durability don't change whether the wood is brown, silver, or anywhere in between. A greyed Thermowood board at year ten performs exactly as it did the day it was installed.
Two finishing choices, two opposite goals
Thermowood takes finishing products exceptionally well because the thermal modification process opens the cellular structure, letting treatments absorb deeply rather than sit on the surface. We offer two in-house finishing options, each designed for a different customer intent.
Both cost $1 per linear foot and add two to three business days to your lead time.
Option 1 — Valhalla Lifetime Wood Sealer (accelerated silvering)
Split image: Valhalla Lifetime Wood Sealer product on left, silvered board close-up on right.
Valhalla is a penetrating, plant-based sealer designed to accelerate and even out the natural silvering process. Rather than preserving the original brown, it takes Thermowood to its final silver-grey state within weeks rather than years — and does so uniformly across all elevations of a building.
Why choose accelerated silvering:
- Skip the transitional phase. Your facade looks "finished" immediately — no patchy 18-month period where the wood is half-brown and half-silver.
- Even coloration across all elevations. South and north faces reach the same silver tone at the same time, rather than the south racing ahead.
- Matches architect renderings day one. If the project is specified in silver, the building looks correct on the day it's clad.
- Penetrating, not film-forming. Absorbs into the wood rather than sitting on top — so it can't peel, crack, or bubble.
- Water repellence and mildew resistance are included in the treatment — even though the primary purpose is cosmetic silvering.
- Plant-based and zero VOC. Safe for soil contact and food-adjacent applications.
- Essentially maintenance-free once applied. The silver it creates is the silver Thermowood was going to reach anyway — you've just accelerated the timeline.
Best for: Contemporary Nordic-inspired facades, coastal projects, rooftop terraces, any project where you want the wood to look like wood that's been there for a while from day one.
Wide architectural shot of a building clad in Valhalla-silvered Thermowood. Aspirational.
Option 2 — PPG Proluxe (preserving the brown)
Split image: PPG Proluxe product on left, Proluxe-finished board close-up on right.
If the project calls for the rich caramel-brown to remain, Proluxe (formerly sold as Sikkens) is the industry-standard premium finish. It forms a translucent, UV-resistant film that blocks the sunlight responsible for silvering while still allowing the grain to show through.
Why choose Proluxe:
- Preserves the original brown. With regular reapplication, the wood stays within 10-15% of its fresh-milled tone indefinitely.
- Rich color depth. The slight film thickness gives Thermowood a deeper, more saturated appearance than natural or oil-only finishes.
- Tonal range available. Ships in our shop-standard natural, plus cedar, walnut, or custom tones on request — contact us for samples.
- Strongest UV protection of any finish in this class.
Reapplication: Proluxe requires a maintenance coat every 2-3 years on exposed elevations to maintain the color. This is standard for any brown-preserving wood finish — the UV that would naturally silver the wood is also what breaks down the finish protecting it. Interior installations (sauna, paneling) effectively never need recoating.
Best for: Projects where the brown wood aesthetic is essential and the client is comfortable with a standard wood-finish maintenance cycle. Also appropriate for interior applications where UV is minimal and reapplication is rarely needed.
Wide architectural shot of a building with rich brown preserved by Proluxe.
Comparison at a glance
| Natural (no finish) | Valhalla | Proluxe | |
|---|---|---|---|
| Price | Included | $1/lft | $1/lft |
| Final color | Silver (after 1-3 yrs) | Silver (immediately, uniform) | Brown (maintained) |
| Transitional look | Uneven, 18+ months | None — silver day one | None — brown throughout |
| Maintenance | None, ever | None, effectively | Recoat every 2-3 yrs |
| VOC content | None | Zero | Low |
| Can fail visually | No | No (penetrating) | Eventually, without recoat |
Ordering with finishing
When you place your order, select the finishing option in the product options. Your boards will be milled, finished in our Greenville facility, allowed to cure for 24-48 hours, and shipped — typically adding two to three days to standard lead time. Large orders (1000+ linear feet) may add an additional day.
Boards being finished in-house. Shows the "manufacturer-direct" story is real.
If you'd prefer natural weathering, you don't need to do anything. Thermowood ships unfinished by default and will begin its transition to silver-grey once installed.
Which should I choose?
Choose natural (no finish) if: you love the journey from brown to silver and don't mind the 1-3 year uneven transition, you have a tight budget, or you want the lowest environmental footprint possible.
Choose Valhalla if: you want the silver look and you want it now, you want all elevations to grey together rather than unevenly, or you're cladding a project where the wood needs to look "settled in" on day one.
Choose Proluxe if: you want to preserve the rich brown color, you have a specific tonal target (walnut, cedar), or the client prefers the warmth of wood-colored wood over silver.
Still unsure?
Open sample box showing natural, Valhalla, and Proluxe swatches side by side.
Order a sample box and we'll include swatches showing the same board in three states: fresh-milled natural, Valhalla pre-silvered, and Proluxe-finished. See all three side by side under your project lighting before you commit.
Questions about finishing specific to your project? Email sales@stickssupply.com or call 864-202-6710.