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Good trim work looks effortless, but it depends on precision: inside corners that stay closed, joints that don't open after the first winter, baseboards that follow a floor that is never perfectly flat, and a paint finish without gaps or brush marks. In older homes it also means matching profiles that stores stopped selling long ago and handling old paint with care, since it may contain lead.
This page covers the main types and profiles, the choice between wood, MDF and PVC, how a finish carpenter installs trim, seasonal gaps, matching original trim, painting and the precautions for lead paint. Crown moulding also has its own page for larger ceiling details.
Types of trim and moulding: baseboards, casings, crown and more
Each piece of trim has a job, and its profile, the shape you see at the end of a piece, sets the style. Plain, square-edged profiles suit modern rooms, while stepped, curved and layered profiles suit traditional ones. Keeping profiles consistent from room to room matters more than any single choice.
- Baseboards: along the bottom of the wall, hiding the gap at the floor and taking knocks, sometimes finished with a small shoe or quarter-round moulding.
- Casings: around doors and windows, covering the joint between the frame and the wall.
- Crown moulding: at the joint between wall and ceiling, usually set at an angle; the crown moulding page covers it in depth.
- Window stool and apron: the interior ledge at the bottom of a window and the trim piece beneath it.
- Chair rails and wainscoting: a horizontal rail across the wall, sometimes with panelling below, that protects the wall and divides it visually.
- Built-up trim: several simple mouldings layered to create a larger, richer profile, common in older homes.
Trim materials: MDF, solid wood and PVC for wet areas
The material decides how trim looks under paint or stain, how it stands up to knocks and how it reacts to moisture. Many homes mix materials, using one product in the living areas and another in rooms that get wet.
- MDF: smooth, stable and usually sold primed, a common choice for painted trim in dry rooms, but it dents more easily than hardwood and swells if its edges soak up water.
- Finger-jointed pine: short lengths of pine glued end to end into straight, stable pieces meant for painting.
- Solid softwood such as pine: easy to cut and shape, and suitable for paint or stain.
- Hardwoods such as oak or maple: harder and heavier, chosen for stained trim that shows the grain and for high-wear spots.
- PVC: unaffected by water, so it suits bathrooms, laundry rooms, basements and entrances where floors are mopped often or get wet.
- Matching an existing house: older trim is usually solid wood, so a close match may call for the same species or a custom profile.
How trim is installed: coped corners, scribing, nail and fill, caulk
A finish carpenter starts by reading the room, not by cutting. Walls bow, corners are rarely square and floors dip, and trim has to follow all of it without looking forced. The work then follows a familiar sequence.
- Inside corners: coped rather than mitred on baseboards and crown, meaning one piece is cut to the exact outline of the other's profile so the joint stays tight as the house moves.
- Outside corners and casings: joined with mitres, usually glued as well as nailed, so the corners stay closed.
- Scribing: the bottom of a baseboard traced and trimmed to follow an uneven floor, or the edge of a piece shaped to meet a wavy wall.
- Nail and fill: trim nailed into the framing with a finish nailer, then the small holes filled flush and sanded.
- Caulk: a paintable caulk run along the joint between trim and wall to close hairline gaps, not to hide badly cut joints.
- Final prep: a touch-up of primer on filler and bare spots so the paint goes on evenly.
Why trim joints open up in winter, and how installers limit it
In a Canadian house, dry heated air in winter and humid summers make wood trim and the framing behind it shrink and swell. Mitred corners and the butt joints along long runs are where that shows first, as thin gaps that open when the heat comes on and may close again in summer.
Installers limit the problem by letting trim sit in the house for a while so it adjusts to indoor conditions, coping inside corners, gluing mitres and fastening into solid framing rather than just drywall. A flexible caulk handles the small movement that remains. If joints open wide every winter, the house may simply be very dry, which is worth checking with a hygrometer.
Matching or restoring original trim in older homes
Original trim is often wider, thicker and more detailed than what stores stock today, and a single damaged length replaced with a modern profile stands out at once. Before anything comes off the wall, ask whether it can be repaired in place: gouges filled, a new section spliced in or loose pieces refastened.
When new pieces are needed, there are several routes: a stock profile that comes close, a built-up profile assembled from several simple mouldings, a custom profile reproduced by a millwork shop, or trim salvaged from a closet or a less visible room. Keep any piece you remove as a sample, since a profile is far easier to copy from the real thing than from a photo. In a home with a heritage status, check what approvals apply before original woodwork is removed; the plaster repair page covers the Quebec rule for classified buildings.
Painting trim and baseboards for a durable finish
Trim takes more wear than walls, so it is usually painted in a harder, more washable finish such as satin or semi-gloss, which wipes clean easily but shows flaws more readily. New trim is best primed on every face before installation, especially MDF and anything going into a damp room, then finished in place once it has been filled and caulked.
Existing trim needs cleaning and a light scuff, and trim finished in oil-based paint needs a bonding primer before water-based paint will stick. The interior painting page explains how to tell which kind of paint is on your trim and how a painter sequences walls, trim and doors. Stained wood trim is a different job: filler has to match the wood, and the finish is a clear coat rather than paint.
Lead paint on old trim: test it and don't sand it
Trim is where old paint piles up. Baseboards, casings and window trim were repainted over and over, and in older homes the bottom layers may contain lead. Health Canada says a home built before 1960 probably contains lead-based paint and warns against using sanders, heat guns or blowlamps to remove it, because they create toxic dust and fumes containing lead.
Pulling off old trim also cracks the paint film where it meets the wall, and windows and doors that rub grind painted surfaces into fine dust. Have the paint tested before anyone sands, scrapes, strips or removes trim in an older home, and ask the contractor how chips and dust will be contained and cleaned up if lead is found.
Trim & Moulding: frequently asked questions
What's the difference between a coped and a mitred corner?
A mitre joins two pieces cut at matching angles, which works well on outside corners but tends to open on inside corners as the house moves. A coped joint shapes one piece to fit the profile of the other, so it hides movement and out-of-square walls better.
Is MDF baseboard a good choice for a bathroom or basement?
It's risky where floors get wet, because MDF swells when water reaches its edges or bottom. PVC or a well-sealed wood is the safer choice in bathrooms, laundry rooms and basements that have ever taken on water.
How are baseboards installed on an uneven floor?
The carpenter scribes the bottom edge, tracing the floor's contour onto the baseboard and trimming to that line, so it sits tight along its whole length. A flexible shoe moulding can also cover small dips.
Can new trim be matched to the original trim in an old house?
Usually, yes. A close stock profile, a profile built up from several mouldings or a custom reproduction from a millwork shop can all work. Bring a real sample rather than a photo, and expect custom work to take longer to arrange.
Should trim be painted before or after it is installed?
Often both. Priming, and sometimes a first coat, before installation is faster on long lengths, while the final coat goes on afterward to cover the filled nail holes, the caulk and any marks from handling.
Is it safe to remove old painted trim myself?
In a home built before 1960, have the paint tested first, since Health Canada says such homes probably contain lead-based paint. If lead is present, avoid sanding or heat-stripping and let a contractor who knows lead-safe practices handle the removal and cleanup.
Sources
Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides