Never Replace Original Old-Growth Fir with MDF: A Colorado Springs Contractor's Case for Historic Trim

I learned wood finishing refinishing pianos with my father. The lesson that transferred most directly to construction work was this: the material under the finish is everything. You can apply the most beautiful topcoat in the world, and if what’s underneath it is inferior, the finish will reveal it eventually — through movement, through texture, through the way light hits it on a clear day.

Old-growth fir trim in Colorado Springs homes built before 1950 is some of the finest building material I’ve encountered in 15 years of construction work. The baseboards, door casings, window trim, and built-ins in Old Colorado City bungalows, Old North End Victorians, and Manitou Springs Craftsmans were milled from trees that took two to five centuries to grow. That growth rate produced wood so dense, so tight-grained, and so dimensionally stable that it has survived 80–100 years of Colorado’s climate extremes while modern lumber in the same homes requires replacement every decade.

Replacing it with MDF is a mistake. Here’s why — and what to do instead.

What Old-Growth Fir Actually Is

Douglas fir is not a single material. The Douglas fir sold at lumber yards today is harvested from plantation-grown trees that were planted 20–40 years before cutting. These trees grew fast, produced wide annual rings, and yielded lumber that is soft by comparison, prone to checking, and significantly less stable than its predecessor.

Old-growth Douglas fir was harvested from trees that grew slowly in old-growth forests — often 200–500 years old at the time of cutting. The slow growth produced annual rings so tight they’re practically invisible to the naked eye. This tight grain structure creates a fundamentally different material:

Density: Old-growth fir is 2–3 times harder than modern plantation fir. A fingernail pressed into it leaves no mark. The same pressure on modern dimensional lumber leaves a visible dent. This density is why old-growth trim has survived 100 years of impact — doorframe edges, baseboard kicks, window sill wear — without significant damage.

Stability: Dense, tight-grained wood moves less with humidity changes than open-grained wood. In Colorado Springs, where indoor humidity swings from 10–20% in winter to 40–60% during monsoon months, dimensional stability matters enormously. Old-growth fir trim that was installed in 1920 is still the same dimensions it was installed at. Modern lumber in the same conditions would have moved visibly.

Finish quality: The tight grain of old-growth fir accepts stain and finish with exceptional uniformity. The result is a depth and clarity of finish — whether natural wood finish or paint — that modern lumber and engineered products cannot replicate. Paint on old-growth fir holds adhesion longer, cracks less, and looks better through more repaints than paint on modern lumber or MDF.

Why MDF Is the Wrong Answer in Colorado Springs Specifically

MDF — medium density fiberboard — has become the default trim material for new construction and renovation across much of the country because it’s dimensionally precise, takes paint well immediately after finishing, and is inexpensive. It’s the right material in moderate climates with stable humidity.

Colorado Springs is not a moderate climate with stable humidity.

Indoor humidity in Colorado Springs drops to 10–20% relative humidity in winter — some of the driest indoor conditions in the contiguous United States. At those humidity levels, MDF — which is made from compressed wood fiber held together with resin — shrinks. The resin bonds between fibers stress as the material contracts. At seams, corners, and mitered joints, this shrinkage manifests as cracking paint, opening gaps, and in severe cases, surface delamination.

Then summer arrives and indoor humidity climbs, particularly during July and August monsoon months. The MDF swells as it reabsorbs moisture. Paint that was already stressed from winter shrinkage cracks further. Mitered joints that opened over winter won’t fully close again because paint and caulk have been forced into the gaps.

Over three to five cycles of Colorado’s humidity range, MDF trim in a Colorado Springs home looks noticeably worse than when it was installed. The paint cracking at joints and corners that homeowners describe as “normal settling” is often MDF responding to humidity swings it wasn’t designed to handle.

Old-growth fir in the same home, in the same location, after the same five years: unchanged. The density and stability that made it the default building material for a century are the same properties that make it indifferent to Colorado’s humidity swings.

The Irreplaceability Problem

This is the point that matters most: you cannot buy old-growth fir. It doesn’t exist as a commercial product. Every tree that produced it was harvested generations ago. The old-growth forests that produced it are gone or protected. What’s in older Colorado Springs homes is a finite, non-renewable resource.

The architectural salvage market offers some reclaimed old-growth lumber — salvaged from demolitions of older buildings — but availability is limited, selection is inconsistent, and matching specific profiles requires custom milling. For large-scale replacement, it’s often impractical.

When old-growth fir trim is removed from an older Colorado Springs home and replaced with MDF profiles, the original material is gone. The character, the density, the finish quality, and the century-proven durability — gone. What replaces it will look acceptable for a few years and require replacement again within a decade.

What to Do With Damaged Old-Growth Trim

The appropriate response to damaged old-growth fir trim depends on the nature and extent of the damage.

Painted over: The most common situation. Old-growth fir trim under paint — sometimes five or six layers of paint over 80 years — can be stripped and refinished to reveal the original wood. The process is labor-intensive. Profiled surfaces require careful work with chemical stripper, heat guns, and detail scrapers to remove paint from inside coves and shadow lines without damaging the wood beneath. But the material revealed after stripping is often exceptional — tight grain, warm color, and a finish quality that rewards the labor investment.

Physically damaged: Dings, dents, and gouges in old-growth fir can often be filled and refinished because the material is hard enough that damage tends to be localized rather than widespread. Epoxy wood filler, sanded smooth and finished to match, is virtually invisible on painted old-growth trim.

Missing sections: Small missing sections — a chipped corner, a damaged miter — can be built up with filler, shaped to profile, and finished to match. Larger missing sections are harder. If replacement lumber is needed, architectural salvage is the first stop. If salvage isn’t available, accepting a visual distinction at the replaced section — rather than replacing the entire run with inferior material — preserves the original where it exists.

Water damaged: Old-growth fir that has been chronically wet — typically at window sills below failed glazing, or at baseboards near floor-level plumbing leaks — can be soft in localized areas while the surrounding wood remains sound. Assessment determines whether the damaged section can be consolidated, rebuilt, or must be replaced. Structural epoxy consolidants and fillers work well on localized soft areas in otherwise sound old-growth trim.

When Replacement Is Genuinely Necessary

There are cases where original trim cannot be saved: extensive rot throughout, physical damage that compromises profile integrity, or missing sections too large to practically fill. In these cases, the choice of replacement material matters.

Not MDF. For the reasons described above, MDF in Colorado Springs conditions will require replacement again within a decade. It is not a solution; it is a deferral.

Solid wood: Poplar is the standard paint-grade solid wood trim material for new installations — stable, hard enough to accept paint well, and far more durable than MDF in variable humidity. It doesn’t match old-growth fir in density or character, but it won’t fail in five years either.

Salvaged old-growth: For historically significant spaces where matching the original is important, architectural salvage dealers in Colorado Springs and Denver occasionally have matching profiles or close approximations. This requires lead time and flexibility on availability.

Primed MDF for low-humidity-risk locations only: Interior locations away from exterior walls, above the floor line, and away from moisture sources — crown molding in a climate-controlled living room, for example — are lower risk for MDF. These locations don’t experience the humidity extremes that cause failure at baseboards and window trim. Even here, solid wood is preferable, but MDF is more acceptable than at high-risk locations.

A Note on Colorado Springs Historic Districts

Several Colorado Springs neighborhoods have historic designation: Old North End, Old Colorado City, and portions of Manitou Springs. In designated historic districts, exterior alterations typically require Historic Preservation Board review, and some interior alterations to contributing structures may also be subject to review depending on the specific designation.

If your home is in a historic district and you’re considering significant trim work, confirm with the City of Colorado Springs Historic Preservation Office before proceeding. Removing original material from a contributing structure in a historic district may require documentation and review even for interior work.

For a free assessment of historic trim in your Colorado Springs home — refinishing, repair, or appropriate replacement — call (719) 243-9718.