MDF vs. Solid Wood vs. PVC: Which to Buy?
Walking into the trim aisle, you'll see three main materials. Choosing the wrong one for your specific room is a classic DIY mistake.
- MDF (Medium Density Fiberboard): The most popular choice. It is cheap, perfectly smooth, and paints beautifully. The catch: MDF acts like a sponge. If it gets wet (from a leaky toilet, a wet mop, or high humidity), it will swell and crumble. Never use MDF in a full bathroom.
- Solid Wood (Pine, Poplar, Oak): Beautiful, durable, and can be stained. It holds up much better to moisture than MDF. However, it is expensive, prone to knot-holes, and requires more prep work (sanding, knot-sealing) before painting.
- PVC / Cellular Vinyl: The ultimate solution for bathrooms, basements, and exterior trim. It is 100% waterproof, rot-proof, and insect-proof. It paints well but can expand and contract significantly with temperature changes, so leave a tiny gap at the ends.
The "Miter Cut" Waste Factor
Unlike flooring, where you can use a small off-cut to start the next row, trim waste is permanent. Every time you cut a 45-degree miter for an inside or outside corner, you lose length. If you mess up a cut on an 8-foot piece, you often have to throw the whole piece away.
Pro Tip: The Corner RuleFor a simple, square bedroom, a 10% waste factor is perfect. If your room has lots of alcoves, bay windows, or outside corners (which are notoriously tricky to cut), bump your waste factor up to 15% or 20%. It is much cheaper to return one uncut stick of trim than to run back to the store halfway through your project.
The "Caulk & Fill" Secret (Pro Finishing)
Have you ever wondered why a contractor's baseboards look like one continuous piece of expensive wood, while a DIYer's look like separate boards with gaps? The secret isn't the wood; it's the caulk and filler.
- Top Gap: Walls are rarely perfectly straight. There will be a gap between the top of the baseboard and the drywall. Run a bead of paintable latex caulk along the top edge and smooth it with a wet finger. This hides the gap completely.
- Nail Holes & Joints: Fill every nail hole and every miter joint with paintable wood filler (not caulk, caulk will shrink and crack in the joints). Sand it smooth once dry.
- Prime and Paint: Once caulked and filled, one coat of primer and two coats of semi-gloss paint will make cheap MDF look like a $10/ft custom installation.
Common Project Types & How to Measure Them
Trim projects vary wildly. Here is how to use our calculator for the most common scenarios.
- Standard 12x15 Bedroom: Enter 15 for length, 12 for width. Set doors to 1 (standard 2.5 ft width). Use a 10% waste factor. This will give you the exact linear feet of baseboard needed for the entire room.
- Crown Molding (Complex): Crown molding requires "coping" cuts for inside corners, which generates a lot of waste. Measure your room perimeter normally, but always use a 20% waste factor for crown molding. It is much more expensive than baseboard, so accurate measuring is critical.
- Window Casing: Measure the height and width of the window opening. Add 6 inches to both the height and width to account for the "horns" (the little bits of trim that stick out past the top corners). Multiply by the number of windows to get your total linear feet.
Frequently Asked Questions
Should I nail trim to the wall or the studs?
Always nail trim to the wall studs. Use a stud finder to locate them, and shoot your finish nails directly into the wood. If you only nail into the drywall, the trim will eventually pull away from the wall as the house settles.
What length nails should I use for baseboard?
Use 2-inch to 2.5-inch 15-gauge or 16-gauge finish nails. This length is long enough to bite deep into the wall studs, but short enough that you won't accidentally hit electrical wiring or plumbing running through the center of the wall.
Can I install baseboard over carpet?
It is highly recommended to remove the carpet and tack strip first. Installing baseboard over carpet looks unprofessional, leaves a gap when the carpet is eventually replaced, and prevents you from nailing securely into the bottom plate of the wall.
How do I cut trim for outside corners?
Outside corners require two 45-degree miter cuts that meet at a 90-degree angle. Use a miter saw set to 45 degrees. Test the fit on the floor before nailing. If your walls aren't perfectly square (they rarely are), you may need to adjust the angle slightly (e.g., 44 or 46 degrees) to get a tight fit.
Do I need to prime MDF trim before painting?
Most MDF trim comes "primed" from the factory, but it is still highly recommended to apply a coat of high-quality primer before your topcoat. MDF is very porous, and skipping primer will result in a blotchy, uneven paint finish.