When a project calls for custom trim work — real profiles, routed edges, built-up crown, detailed water tables — the material matters as much as the craftsmanship. For years, that meant wood. And wood has its limitations. It rots. It splits. It moves with moisture and temperature in ways that cause caulk joints to open up and paint to fail prematurely.
At IES Construction & Roofing, when a project calls for custom exterior trim work, we reach for TruExterior by Westlake Royal Building Products — a poly-ash composite that machines like wood and outperforms it in every way that matters on the exterior of a St. Louis home.
What Is TruExterior?
TruExterior is a trim and siding product made from a proprietary blend of fly ash and polymer — a combination called poly-ash. It was originally developed by Boral Industries, which discovered that fly ash — the byproduct of coal combustion — could be cleaned, processed, and combined with a bio-based polymer to produce a building material with remarkable characteristics. Westlake Royal Building Products now manufactures and markets the product line.
The result is a material that looks and works like wood but is made entirely of inorganic components. There is no wood fiber in TruExterior. And that changes everything about how it performs on the exterior of a home.
How It’s Made
Fly ash is a fine powder byproduct recovered from coal-fired power plants. On its own it has no structural value — for decades it was stored in containment ponds or buried in landfills. Boral developed a process to clean and process that fly ash and combine it with polymer resins under controlled conditions to produce a dense, stable composite board.
The resulting poly-ash material contains approximately 70% recycled content — making it one of the more sustainable exterior trim options available. It comes from the factory pre-primed and ready to paint, cut, mill, or route on the job site.
Why We Use It
The reason IES reaches for TruExterior on custom trim work comes down to a few things that matter on every exterior project we touch.
It Does Not Rot or Decay
Because TruExterior contains no wood fiber and no organic material, there is nothing in it for rot, mold, or insects to consume. Termites won’t touch it. Wood-boring insects have no interest in it. It can be installed in ground contact applications — you could bury it and it would be fine — which is more than you can say for any wood-based trim product.
For St. Louis homeowners, where summer humidity is relentless and trim at grade level takes a beating from sprinklers, mulch, and seasonal moisture, this matters in a real way.
It Doesn’t Move
Wood expands and contracts with moisture cycling — absorbing water when it’s humid, drying out when it’s not. That movement is what opens caulk joints, causes paint to crack, and leads to callbacks. TruExterior has virtually no expansion and contraction. Joints stay tight. Paint stays intact. The installation looks the same in August as it does in February.
It Runs Through a Router
This is where TruExterior becomes something special for custom work. Because it has the density and consistency of a fine-grained composite, it machines like wood — table saw, miter saw, router, shaper. You can run custom profiles through it just like you would with wood, and the edges come out clean and crisp.
At IES, we’ve used this capability on projects that required something no stock trim profile could deliver. On our Clay Avenue restoration in Kirkwood — an 1883 Victorian Farmhouse with specific historic trim requirements — we ran custom water table profiles through TruExterior to match the proportions and character of the original woodwork. On our Starbuck Road project, we used TruExterior to produce custom crown molding profiles that fit the architecture of that specific home.
No stock profile off a shelf. Custom work, machined in the field, from a material that will never rot.
No End Sealing Required
One of the most common points of failure with primed pine and other wood trim products is cut ends — when you cut a board in the field, you expose raw wood that needs to be sealed before installation or moisture will wick in and cause failure from the inside out. TruExterior does not require end sealing. Cut it, install it, paint what you can see. That’s it.
Where We Use It
At IES Construction & Roofing, TruExterior shows up on our projects in a few consistent ways:
- Fascia boards and trim boards at cornice lines
- Water tables at the base of siding runs
- Custom crown molding profiles at eaves and gable ends
- Skirt boards and transition trim at grade level
- Window and door surrounds
- Any application where a custom routed profile is required
Paired with James Hardie fiber cement siding, TruExterior gives us a complete exterior system — both products inorganic, both rot-resistant, both low-maintenance, and both paintable to any color the homeowner chooses.
The Bottom Line
TruExterior is not the cheapest trim option on the market. It costs more than primed pine. But when you factor in the longevity, the elimination of rot callbacks, the stability of the installation over time, and the ability to produce custom profiles that wood would otherwise require — it earns its place on every project where the trim work matters.
If you’re planning an exterior renovation on a St. Louis or Metro East Illinois home and want to talk through material options — including where TruExterior might be the right call — we’re happy to walk you through it at your free estimate.