Thermally Modified Ash: Plan for Appearance Changes Over Time

The Natural Weathering Process of Thermally Modified Ash

When left untreated and exposed to the elements, thermally modified ash will gradually transition in color. Initially, it presents a natural, deep brown hue. Over time, UV radiation and moisture exposure will cause the wood to lighten and develop a silvery-gray patina. This process is often referred to as 'silvering' or 'greying out' and is a natural characteristic of many wood species exposed outdoors.

The rate and uniformity of this weathering can vary depending on several factors: the amount of direct sunlight, exposure to rain, and regional climate conditions. Areas more exposed to sun and rain will typically weather faster and potentially more unevenly than sheltered areas. For example, a south-facing wall will likely silver more quickly than a north-facing one, and protected soffits may retain their original color for longer. This variation can create a dynamic, natural aesthetic, but it's important to anticipate if a uniform appearance is desired.

Maintaining the Original Deep Brown Hue

If the goal is to preserve the initial deep brown color of thermally modified ash, regular application of a UV-protective finish is necessary. These finishes typically contain pigments and UV inhibitors that shield the wood from the sun's rays, slowing down the silvering process. However, maintaining the original color is an ongoing commitment.

The frequency of reapplication depends on the specific product used, the level of sun exposure, and local climate. Generally, finishes may need to be reapplied every 1 to 3 years. It's crucial to follow the finish manufacturer's instructions for preparation, application, and reapplication to ensure proper adhesion and protection. Before reapplication, the surface typically needs to be cleaned and potentially lightly sanded to remove any dirt or loose fibers.

Embracing the Silver Patina

Many designers and homeowners intentionally choose to let thermally modified ash weather naturally to a silver-gray. This low-maintenance approach eliminates the need for recurring finishing treatments. The resulting patina can offer a sophisticated, timeless look that blends well with various architectural styles and natural landscapes.

While the silvering process reduces ongoing maintenance for color preservation, the wood still benefits from periodic cleaning to remove dirt, mildew, and other surface contaminants. A simple wash with mild soap and water can help maintain a clean appearance. Ensure proper drainage on vertical surfaces to prevent water pooling, which can lead to uneven weathering or biological growth.

Cleaning and Restoration Options

Over time, any outdoor wood surface can accumulate dirt, grime, and mildew. For thermally modified ash, regular cleaning helps preserve its appearance, whether it's kept natural or finished. A soft brush or sponge with a solution of mild detergent and water is often sufficient for routine cleaning. Rinse thoroughly with clean water.

For more stubborn stains or to refresh a weathered surface before applying a new finish, specialized wood cleaners designed for exterior use can be effective. Always test any cleaning product on an inconspicuous area first to ensure it does not negatively affect the wood's color or texture. If a finished surface has deteriorated, stripping the old finish may be necessary before applying a new one, following the finish manufacturer's instructions.

Worked Example: Planning for a Facade's Appearance Over Time

Consider a hypothetical residential project featuring thermally modified ash cladding on two distinct elevations: a main facade facing south and a covered porch ceiling facing north.

For the south-facing main facade (e.g., 20 feet wide by 10 feet high), which receives direct sunlight and rain, the client desires to maintain the deep brown color for as long as possible. This will require selecting a high-quality UV-protective exterior oil or stain. Based on manufacturer recommendations for similar products, reapplication might be needed every 1-2 years. The total surface area is 200 square feet. This calculation helps plan for recurring material costs and labor for maintenance.

For the north-facing covered porch ceiling (e.g., 12 feet by 8 feet), which is largely protected from direct sun and rain, the client prefers to let the wood naturally silver. This choice eliminates the need for periodic finishing. However, they understand that while the silvering will be slower and potentially less pronounced than on an exposed wall, occasional cleaning (perhaps every 2-3 years) will still be beneficial to remove any dust or cobwebs and maintain a fresh appearance. This approach minimizes long-term maintenance effort and material costs for this specific area.

Before you order

• Desired initial appearance: Deep brown or natural variation?
• Tolerance for color change: Will a silver-gray patina be acceptable or preferred?
• Maintenance commitment: Are you prepared for regular reapplication of finishes?
• Exposure levels: How much direct sun and rain will each surface receive?
• Finish type: If maintaining color, research suitable UV-protective oils or stains.
• Cleaning plan: How often will surfaces be cleaned, regardless of finish?
• Budget for maintenance: Include costs for finishes, cleaners, and labor over time.

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

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