TRIM, INTERIOR - home CONTENTS: Interior trim types, baseboard, quarter-round, door and window casings
Definitions of types of interior building trim: Cornice molding, door & window casing, picture rail, plate rail, baseboard trim, quarter-round trim. Properties & purposes of interior trim in buildings. Common problems with interior trim: diagnosis, cause. Tips for installing trim against uneven floor or ceiling surfaces. How to preserve and re-use valuable antique or historic wood trim in buildings.
The building interior trim types and interior trim defects or problems described here are adapted and expanded from original citations provided courtesy of Carson Dunlop Associates, Home Reference Book, with permission.
[Click to enlarge any image]
The Functions of Interior House Trim
Most houses have interior trim including baseboard, quarter round and door and window
casings. These trim details protect and conceal joints, corners and changes in material.
Interior trims conceal rough cuts and edges in plaster and drywall around windows and doors and at the floor/wall or ceiling/wall juncture. They add architectural appeal to a home, and better quality moldings and trim may indicate better quality construction.
Carson Dunlop's sketch (above left) illustrates the location of the principal types of interior trim:
Definition of Cornice molding trim - at the intersection of the wall top and room ceiling
Definition of Door casing (or window casing) trim - surrounding doors or windows on the building interior
Definition of Picture molding (not shown) - horizontal trim located approximately 12" below the ceiling in Victorian era homes. The molding profile provides a shape that permitted use of flat S-hook used to hang pictures on the wall below. Pictures hung using picture molding used exposed hanging wires, often decorative themselves. Picture molding permitted hanging and even moving pictures on the room walls without damaging the wall plaster by nails.
Definition of Plate rail - horizontal trim located high on the room walls, of adequate width and including a groove that permitted support of decorative ceramic plates or similar near-flat objects. Typically you would not find both a plate rail and picture molding on the same wall. Expect to find picture molding in Victorian era homes and plate rails in Colonial era style homes.
Definition of Baseboard trim - horizontal trim boards at the wall-floor intersection
Definition of quarter-round trim - horizontal trim strips, typically 1/2" in radius, nailed at the intersection of the baseboard trim and the floor. Quarter-round trim is flexible enough to be bent to follow irregularities in the floor surface while closing any gaps between the inflexible baseboard trim and the irregular floor below.
Interior Trim: Tips, and Tricks of the Trade for Installing Interior Trim in buildings
Our photo (left) shows ornate plaster wall, cornice, and ceiling trim details photographed in a home in Mexico City.
Trim Fitting Tips:
Our mentor, Bernie Campbalik, taught his student carpenters that if the building walls or floors are not dead flat, fitting some wood trim boards perfectly can be difficult or impossible. But a few tricks of the trade can still produce beautifully-fitted interior building trim. We describe a few basic trim fitting ideas here.
Fitting Trim to an Uneven Floors or Ceilings:
If the wall is flat but the floor sags or humps, it is often possible to push more narrow boards trim down flush with the floor or up flush with the ceiling surface or close to flush with the floor or ceiling during nailing. Where the trim boards are wider or heavier stock that bending is impossible.
To fit heavier trim boards to an uneven floor surface we used two alternatives: the trim board can be scribed and custom cut or planed to meet the floor surface variations, or a smaller-gauge quarter-round additional trim strip can be nailed in place at the juncture of the larger trim baseboard and the floor. It's easy to bend quarter-round trim to accommodate wall/floor irregularities.
Fitting Trim to an Uneven Wall:
Sometimes we [DJF] found that the building walls were scalloped or bulged, perhaps because of uneven drywall installation over wall studs that were not in a flat plane, or in some older homes that were insulated using foamed-in wet urethane during the 1970's we found that the moisture of the insulation process caused a scalloping effect in the wall drywall after the insulation dried.
To fit floor/wall baseboard trim against a slightly-scalloped wall it may be possible to simply push the trim board tightly against the wall during nailing. But where the wall scallops are deeper, we use a flexible caulk to seal the otherwise dark gap that appears between the inner edge of the trim board and the wall surface.
Baseboard and Quarter-Round Interior Trim
Baseboard and quarter round are usually wood (or wood fiber) components installed at wall/floor intersections.
Baseboard protects the bottom of the walls from things like feet, brooms and vacuum cleaners, and provides a clean joint at walls and floors. Baseboard can be anything from a two-inch high piece of plain lumber to an intricate two or three piece architectural molding, 10 or 12 inches high.
Quarter round [not shown in the sketch] is usually relatively small (approximately 3/4 inch radius) and covers the joint between the floor and the baseboard. It may be the same material as the baseboard. Some architectural treatments omit quarter round, and occasionally baseboard is omitted as well.
Solid wood trim boards that are painted or that are intended to be painted are commonly constructed of finger-jointed wood, permitting lower-cost construction of long, straight interior (or exterior) trim boards. Finger-jointed exterior trim, unlike interior finger-jointed trim boards, is exposed to weather and can be less durable - illustrated at TRIM, EXTERIOR CHOICES, INSTALLATION.
Alternatives to Wood Interior Trim
Tile or marble may be used for baseboard. This is an expensive treatment, of course. A commercial treatment occasionally found in homes is broadloom flooring turned up the wall a few inches to form a carpet baseboard.
At TRIM, INTERIOR INSTALLATION we describe other alternatives to solid wood trim including MDF (Medium Density Fiberboard composite trim shown in our photos below), urethane interior trim moldings, and other flexible plastic moldings.
What is the Difference Between Door/Window Casings and Moldings?
Door and Window Casings or Trims
Door and window casings provide a finished look to the junction of a wall and door or window opening. Casings on homes built before 1985 [estimated] are most often wood.
Moldings at wall/ceiling intersections are referred to as cornice moldings. They may be made
of wood, plaster or foamed plastic like the urethane molding product shown at left.
Ceiling medallions or rosettes are decorative plaster or foamed plastic details on ceilings around light fixtures. These details were common in principal rooms such as living rooms or dining rooms.
Traditionally ceiling medallions were cast from plaster or were carved from wood. In modern homes ceiling medallions are more often a foam or urethane plastic molding that is lightweight and can be glued to the ceiling surface.
Ceiling medallions also can be fabricated on site although most are pre-manufactured.
Common Problems with Interior Trim
Missing, Loose, or Damaged Interior Trim
Trim can be missing, damaged or loose. Replacement of decorative trim with a matching system may not be practical. Custom millwork is expensive.
Also, some of the woods used in the past are not available today. It may be more cost effective to replace the entire trim in a room.
Tips for Preserving U Re-Using Valuable Antique Wood Trim in Homes
During renovations of a home built in 1900 (photo at left) we had to remove all of the wood trim in order to run additional electrical wiring for receptacle installation.
Because the home was trimmed in beautiful red chestnut wood, we wanted to preserve and re-use the trim boards. Working very carefully using paired flat-bars each trim board was removed without splitting the wood.
Don't try removing trim nails by hammering them back out from the pointed-nail end. Doing so will split the surface of the trim board when the nail head begins to back out.
The finish nails were pulled out of the trim boards from the back side of the board.
When we were ready to nail these antique trim boards back in place we discovered that over the nearly 100 years it had been in place, the wood had become so hard it was like iron, and almost impossible to nail without causing splits. After the first split was observed we changed tactics. Every nail hole was pre-drilled through the trim boards, successfully avoiding any more splitting.
Quarter round is often removed and not replaced when wall-to-wall broadloom is installed. New quarter round is often provided when broadloom is removed.
Plaster trim such as cornice moldings, ceiling medallions, are difficult to repair. Rebuilding or repairing a damaged molding is time consuming and expensive. Replacement of damaged interior trim with a manufactured trim system is often more practical.
Water-Damaged, Stained, or Rotted Interior Trim
Our photos of water damaged interior trim below sow two different examples of visible and hidden results of the effects of wet floors on trim and on drywall located behind floor baseboard trim.
Water damage to interior trim from leaks can stain, damage, and even rot wood trim products. In buildings that have been flooded, even from a brief single-event flood that soaked the building floor, we often find mold damage on the back and under-edge of wood floor baseboard trim boards as well as on drywall found behind the trim boards.
Our photo (left) shows water damaged door casing trim, and you can see that floor baseboard trim to the left of the door casing has been replaced with a plastic trim product.
On a floor exposed to water or dampness, plastic trims offer the advantage of rot and mold resistance.
Watch out: however if there is drywall or drywall behind paneling that is behind the baseboard trim, keep those wall coverings at least 1/2" off of the floor to reduce the chances of moisture or water damage from small spills.
Beadex and Sheetrock-brand tape-on metal corner
beads and trims. Complete line of drywall finishing
Vinyl Corp., A Deitrich Metal
Full line of vinyl beads and trim
Alpine MDF Industries Pty Ltd
ABN 37 064 766 301
Lot 1 Crosher Lane
Wangaratta, Victoria 3677
PO Box 804 Wangaratta,
Australia, Alpine MDF, Tel: +61 (0) 3 5723 0430, Email: email@example.com, produces MDF at a plant North East of Victoria in Wangaratta. Website: http://www.alpinemdf.com.au/
MDF(medium-density fiberboard), polymer, flex, and wood
Classen Vetriebs GmbH, MDF production in Germany
Daiken Corp., New Zealand, Website: www.daiken-nz.com
Georg Gunreben GmbH & Co. KG, MDF production in Germany
HOBATEX GmbH Industrial Partners , MDF production in Germany
Kronoflooring GmbH, MDF production in Germany
Nelson Pine Industries Limited, Auckland
43 Stonedon Drive
East Tamaki, Manukau
PO Box 258 035, Botany
Email firstname.lastname@example.org, Tel: 0800 477 463, produces PrimePanelsNZ, GoldenEdge MDF, exported worldwide, Website: www.nelsonpine.co/nz & http://www.primepanels.co.nz
1 Toronto Street, Suite 600
Telephone: (416) 365-0705
Fax: (416) 777-4419
General Inquiries: email@example.com
Product Information: firstname.lastname@example.org, Website: http://www.norbord.com/,
Norbord produces "Norbord",
produces roof sheathing, wall sheathing, and sub flooring used in North America, and a variety of OSB type products for structural use, flooring, subflooring, and chipboard flooring board products used in europe.
The company's products include a hybrid product comprised of a soft plywood core with a laminate of MDF on both sides, and designed to comply with ANSI/HPVA HP-1-2004 Section 3.12 Formaldehyde Emission Requirements for industrial panels.
Sierra Pine Composite Solutions, produces a variety of particleboard and MDF products. Manufacturing locations are in the U.S. in Georgia and Oegon. Website: http://www.sierrapine.com/. Don't bother trying to find the company's contact information at their website, though the company does list distributors.
Polymer (Urethane), Vinyl Trim Producers & Sources
Polymer moldings and components
Polymer moldings and components
Polymer moldings and components
Polymer moldings and components
Royal Mouldings (formerly Marley Mouldings)
Polymer, polystyrene, expanded-PVC, CPVC, and acrylic
molding profiles and components
Flexible Trim Manufacturers & Sources
Flexible polymer moldings
Flexible polymer moldings
Our page top photo shows antique red chestnut wood trim that was preserved and re-installed in a Poughkeepsie New York Home.
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"An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
Gypsum Construction Guide, National Gypsum Corporation
Construction Handbook [purchase at Amazon.com] H17, Technical
Folder SA920 and PM2, PM3 and PM4, United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Plank House Construction: weblog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
06/12/2007 documented at yurokplankhouse.com where scale model Museum quality Yurok Plank Houses are being sold to raise money for the Blue Creek - Ah Pah Traditional Yurok Village project.
Plastering, PM 5, Product & Systems Technology, US Gypsum, May 1998, web search 10.5.2010, original source: http://www.usg.com/rc/technical-articles/plaster/
United States Gypsum Company, 125 South Franklin ST., PO Box 806278, Chicago, IL 60680-4124,
Paraphrasing from this document: USG uses the term shadowing in this document in describing the visual effect over gypsum board joints caused by the lower moisture absorption rate (take-up) and lower capacity than gypsum base face paper. Shadowing at joints occurs where veneer plaster is applied over tape joints, requiring a second coat to completely hide the tape, providing a visually uniform surface. USG Advises: "This [second] cover coat must be allowed to harden and dry before plaster application is started.