Tongue & Groove
Tongue and groove wood offers a clean, continuous look for walls, ceilings, siding, and other architectural applications. At Mason’s Mill & Lumber, we offer a variety of wood species, profiles, and finishes for both interior and exterior projects.
What Is Tongue & Groove Wood?
Tongue and groove, commonly referred to as T&G, is a milling profile that allows adjoining boards to fit together using a tongue on one edge and a matching groove on the other.
This connection creates a consistent surface with clean lines and a uniform appearance. Depending on the profile and wood species, tongue and groove can complement traditional, rustic, or modern architectural styles.
From traditional Southern Yellow Pine to thermally modified hardwoods and softwoods, our team can help you find the right material for your project.
Browse Tongue & Groove Stock
Thermac Ash Light Roast — CUTEK® Extreme Clear Finish
Thermac Ash Light Roast is a thermally modified White Ash produced by Bingaman & Son Lumber, one of the leading domestic manufacturers of thermally modified hardwoods in North America. Sourced from responsibly managed Appalachian and Pennsylvania forests, the ash is transformed through a chemical-free process that uses only heat and steam — no chemicals, plastics, or additives — sustained for 14–16 hours in an oxygen-deprived kiln. The "Light Roast" designation refers to a lower peak modification temperature, producing a warm caramel-to-amber tone rather than the deeper chocolate brown of a standard or dark roast. The result is a domestic hardwood with the color character of exotic species like teak or light walnut, while retaining more of ash's natural grain contrast and figure.
The performance story is where thermally modified ash really shines. The modification process breaks down the sugars and hemicellulose that fungi and insects feed on, and permanently reduces the wood's ability to absorb moisture — by as much as 45% compared to untreated ash. Independent testing per EN 350 standards rates thermally modified ash at Durability Class 1 ("very durable"), placing it in the same durability tier as tropical hardwoods like teak and ipe, with an expected exterior service life of 25+ years. Dimensional stability improves dramatically as well: radial and tangential shrinkage drop to under 1%, virtually eliminating the cupping, warping, and seam-opening that plague untreated ash outdoors.
Each board is finished with CUTEK® Extreme Clear, a penetrating oil engineered to stabilize exterior wood from the inside out. Rather than forming a surface film like paint or varnish, CUTEK® carries its oils deep into the wood fibers, where they work continuously to slow moisture movement — the primary cause of cupping, checking, and end-splitting. Because the finish penetrates rather than coats, it cannot peel or flake, and maintenance requires no sanding or stripping — just clean the surface and reapply when it looks dry. The clear formulation adds no pigment, allowing the Light Roast's warm caramel tone to show through initially before gradually silvering to a soft gray patina if left unmaintained with a colortone.
Ideal for high-end exterior siding, cladding, soffits, porch ceilings, feature walls, and covered outdoor living spaces where the warmth of a lightly roasted domestic hardwood is preferred over the deeper tones of standard thermally modified ash.
Specifications
| Spec | Detail |
|---|---|
| Species | White Ash (Fraxinus americana) — thermally modified |
| Product Line | Thermac by Bingaman & Son Lumber |
| Modification Level | Light Roast — lower-temperature thermal modification for lighter tone |
| Origin | Appalachian / Pennsylvania hardwood, USA |
| Modification Process | Heat and steam only, no chemicals; oxygen-deprived kiln for 14–16 hours |
| Finish | CUTEK® Extreme Clear (penetrating oil) |
| Finish Type | Oil-based, non-film-forming |
| Color | Warm caramel-to-amber brown; consistent through full board thickness |
| Weathering | Silvers to gray patina over time if not maintained with colortone |
| Durability Class | Class 1 ("very durable") per EN 350 |
| Janka Hardness | ~820–1,325 lbf (varies by modification intensity) |
| Dimensional Stability | Radial shrinkage ~0.1–1.0%; tangential ~0.4–1.0% — significantly improved vs. untreated ash |
| Density | ~554 kg/m³ post-modification (roughly 12% lighter than untreated ash) |
| Equilibrium Moisture Content | ~4–6% (vs. 18–22% for untreated ash) |
| Water Absorption | Reduced 60–70% vs. untreated ash |
| Service Life | 25+ years in exterior applications with proper maintenance |
| Fire Rating | Class B/C flame spread achievable (ASTM E84) |
| Applications | Exterior siding, cladding, soffits, porch ceilings, feature walls, decking, trim |
| Fixings | Stainless steel recommended; pre-drilling advised near board ends |
| Maintenance | Clean and re-oil with Cutek Extreme as needed — no sanding or stripping required |
| Sustainability | Domestic hardwood from sustainably managed forests; chemical-free modification |
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Interior & Exterior Applications
Tongue and groove wood is used across a variety of residential and commercial projects. The right species, profile, and finish will depend on the location and intended use.
Interior Walls & Ceilings
Create warm, continuous wood surfaces for living areas, offices, and architectural accents.
Porches & Covered Outdoor Areas
Bring natural wood character to covered ceilings and other protected outdoor spaces.
Exterior Siding & Cladding
Use exterior-rated tongue and groove materials for architectural siding and cladding applications.
Soffits & Architectural Details
Add consistent wood detailing to roof overhangs, entryways, and architectural features.
Custom Milling& Finishing Options
Every project has different requirements, and standard profiles may not always be the right fit.
Mason’s Mill offers custom milling services for tongue and groove wood in select species, dimensions, and profiles. Our Mill Applied Finishes service also provides finishing options to help prepare materials before delivery.
Share your project specifications with our team, and we can help determine the available options.
Frequently Asked Questions
Tongue and groove boards connect through a tongue on one edge and a matching groove on the other. Shiplap boards use overlapping rabbeted edges. Both can be used for walls, ceilings, and select exterior applications, but they create different joint details.
Yes. Tongue and groove can be used for exterior applications when the wood species, profile, and finishing system are suitable for the intended exposure. Thermally modified wood is one option for exterior siding and cladding.
Mason’s Mill offers options including Southern Yellow Pine and select thermally modified species such as Ash, Spruce, and Pine. Availability varies by profile and product.
Yes. Many tongue and groove products can be painted, stained, or finished with a clear coating. The appropriate finish depends on the wood species, exposure conditions, and desired appearance.
Yes. Our custom millwork team can produce select tongue and groove profiles based on project specifications, wood species, and dimensions.
Yes. Samples are available for select tongue and groove products through our online Sample Shop, allowing you to review the material before placing a larger order.
Find the Right Tongue & Groove Wood for Your Project
Whether you’re working on an interior ceiling, exterior cladding, or a custom architectural detail, Mason’s Mill & Lumber can help you explore available wood species, profiles, and finishing options. Contact our team to discuss your project or request a quote below.