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

I learned wood finishing by refinishing pianos with my father. The lesson that carried straight over to construction work was this: the material under the finish is everything. You can put down the most beautiful topcoat in the world, and if what is underneath it is poor, the finish will show 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. That slow growth produced annual rings so tight they are nearly invisible to the naked eye. This tight grain creates a completely different material:

Density: Old-growth fir is much denser and harder than modern plantation fir. It often has 20 or more growth rings per inch, while fast-grown modern fir has only 3 to 8. Tighter rings mean denser, harder wood. A fingernail pressed into old-growth fir leaves no mark. The same pressure on modern lumber leaves a visible dent (I’ve shown homeowners this trick on their own baseboards, and it’s the moment they finally get why I don’t want to rip this stuff out). That hardness is why old-growth trim has survived 100 years of knocks (doorframe edges, baseboard kicks, window sill wear) without real damage.

Stability: Dense, tight-grained wood is dimensionally stable, meaning it barely changes size as humidity rises and falls. Open-grained modern lumber moves more. In Colorado Springs, indoor humidity drops to 10–20% in winter and climbs during the summer monsoon, so wood here gets worked hard by that swing. Old-growth fir trim installed in 1920 is still the same size today. Modern lumber in the same rooms would have shifted enough to see.

Finish quality: The tight grain of old-growth fir takes stain and finish evenly. The result is a depth and clarity of finish, in either natural wood or paint, that modern lumber and man-made products cannot match. Paint sticks to old-growth fir longer, cracks less, and looks better through more repaints than paint on modern lumber or MDF.

Why MDF Is the Wrong Answer in These Homes

MDF stands for medium density fiberboard. It is wood fiber ground into a paste, mixed with glue, and pressed into smooth boards. It has become the default trim material for new construction because it is cheap, perfectly smooth, and takes paint well right away. In plenty of rooms, it is fine.

The trouble is what MDF does when it meets water, and the fact that you can never repair it. Both of those matter most in exactly the spots where old Colorado Springs homes have their best fir: baseboards and window trim.

MDF has almost no tolerance for liquid water. Get it wet and it soaks the water up like a sponge, swells, and starts to crumble. That swelling is permanent. It does not shrink back when the wood dries out. A mopped floor that splashes a baseboard, condensation running down a window, or a small plumbing drip is enough to ruin a run of MDF (I’ve pulled swollen MDF baseboard out of Colorado Springs homes that was maybe two years old, chewed up by nothing more than a mop bucket). Old-growth fir in the same spot shrugs off the same water.

MDF also dents and chips easily. Its edges and molded shapes are soft. A vacuum cleaner, a chair leg, or a dropped toy that would leave old-growth fir unmarked will crush an MDF corner.

Most important: MDF cannot be refinished. There is no solid wood under the surface, just pressed fiber and glue. Once the smooth skin is dented, gouged, or swollen from water, sanding it only makes it worse. Your only option is to tear the piece out and replace it. Old-growth fir can be stripped, sanded, and refinished many times over.

One myth is worth clearing up: Colorado’s dry winter air is not what wrecks MDF. MDF actually moves very little as humidity rises and falls, less than solid wood does. What ruins it is direct water and physical knocks, and those happen at floor level and at windows, right where the original fir lives.

The Part That Matters Most: You Can’t Buy It Anymore

Here is the point that matters most: you cannot buy old-growth fir. It is not sold as a product anywhere. Every tree that produced it was cut generations ago. The old-growth forests are gone or now protected. What sits in older Colorado Springs homes is a finite resource that will never be made again.

Architectural salvage yards (dealers who resell materials pulled from old buildings before demolition) carry some reclaimed old-growth lumber. But the supply is limited, the selection is hit or miss, and matching a specific trim shape means having it custom milled. For a large job, salvage is often impractical.

When old-growth fir trim is torn out of an older Colorado Springs home and replaced with MDF, the original material is gone for good. The character, the density, the finish quality, the century of proven durability: all gone. What replaces it will look acceptable for a few years, then need replacing 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 built up over 80 years) can be stripped and refinished to bring back the original wood. The work takes time. Molded surfaces need careful work with chemical stripper, heat guns, and detail scrapers to get paint out of the grooves and recesses without damaging the wood underneath. But what shows up after stripping is often exceptional: tight grain, warm color, and a finish that rewards the effort.

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 pieces, like a chipped corner or a damaged mitered joint (the angled cut where two pieces of trim meet), can be built up with filler, shaped to match, and finished. Larger missing sections are harder. If you need replacement lumber, architectural salvage is the first stop. If salvage is not available, letting the patched section look a little different, rather than ripping out the whole run and replacing it with lesser material, keeps the original wherever it still exists.

Water damaged: Old-growth fir that has stayed wet for a long time, usually at window sills under failed glazing (the seal and putty that hold the glass in place) or at baseboards near a floor-level plumbing leak, can go soft in spots while the wood around it stays solid. A close look tells you whether the soft section can be hardened back up, rebuilt, or has to be replaced. A liquid epoxy consolidant (a thin epoxy that soaks into soft wood and hardens it) along with epoxy filler works well on small 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 above, MDF at a baseboard or window will need replacing again within a decade. It is not a fix. It only puts the problem off.

Solid wood: Poplar is the standard paint-grade solid wood trim for new installations. It is stable, hard enough to take paint well, and far more durable than MDF, especially anywhere the trim might get wet. It does not match old-growth fir in density or character, but it will not 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 dry, out-of-the-way spots only: Trim that sits up high, away from exterior walls, and away from any water source (crown molding in a climate-controlled living room, for example) is lower risk for MDF. These spots stay dry and out of harm’s way, so they never see the water and knocks that wreck MDF at baseboards and window trim. Even here, solid wood is the better choice, but MDF is more acceptable than it is in the high-risk spots.

A Note on Colorado Springs Historic Districts

Several Colorado Springs neighborhoods carry historic designation, including the Old North End, Old Colorado City, and parts of Manitou Springs. Here is the good news for interior trim work: in these historic districts, review applies to exterior changes that are visible from the street and need a building permit. Interior renovations are not subject to Historic Preservation Board review. Refinishing, repairing, or replacing your interior fir trim does not need their sign-off.

The rare exceptions are a home that carries its own preservation easement or covenant, or a property that is individually landmarked with specific interior protections written in. If you are not sure where your home stands, a quick call to the City of Colorado Springs Historic Preservation Office will settle it.

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