Door Construction and Assembly

There are a variety of door construction and assembly methods, each with its own benefits.

Hot and Cold Press

Architectural wood doors are constructed using hot press or cold press technology. Controlling the press process is key to door manufacturing consistency and in most cases, certain factors during the cold press process are uncontrollable. In order to assure the greatest degree of control, consistency, and quality in door construction, the hot press technique is preferable.

Hot press technology involves pressing each door individually in a platen under controlled pressure, temperature, and time, based on the type and thickness of material. Hot press produces a uniform bond and uses Type 1 water proof glue versus Type II which is water resistant. Hot press is commonly used for the construction of three- and five-ply doors. Cold press technology, on the other hand, involves pressing a stack or pile of doors, one on top of another, at ambient building temperatures until the adhesives are cured. Depending on the surrounding temperature and humidity conditions, cold pressing takes much longer than hot pressing, and cannot produce doors of equal quantity or quality. With cold pressing, the pressure is uneven and the bottom door in the pile receives more pressure than the top one. In addition, the skins for cold pressing are often outsourced, leading to further loss of control.

Drop-In Assembly

Drop-in core assembly is commonly used in seven-ply door construction and entails dropping the core material into a pre-assembled wood frame. The core must be smaller than the frame which may result in gaps up to ¼ inch wide. Also, the core and frame are not bonded or glued together, or sanded as a unit. In this type of door construction, telegraphing of the door is common.

Loose Lay-Up

Loose lay-up core assembly is also commonly used in seven-ply door construction and involves placing stiles and rails loosely around a core. Because the stiles and rails are not bonded to the core prior to placement of the face materials, gaps up to ¼ inch can occur. In addition, the core, stiles, and rails are not sanded as a unit. Similar to drop-in core assembly, this construction method commonly results in doors with telegraphing.

Bonded Core

In bonded core assembly the stiles and rails are securely glued to the core prior to application of additional plies resulting in no gaps or voids. The assembled core is sanded to plus or minus 0.0005-inch thickness to create a smooth surface that limits the possibility of telegraphing. Bonded core assembly is used in both five-ply and seven-ply door construction.

Ply Construction

Seven-ply wood doors are constructed using pre-manufactured three-ply door skins. The skins consist of a face, crossband, and back veneer. They are applied to each side of a drop-in core assembly using Type II, water-resistant adhesives using cold press technology. The skins are readily available for face materials, which can be birch and oak, rotary cut or plain sliced, and mahogany, plain sliced. Exotic and AA veneer are difficult to source for three-ply skins and are often only available in book and running matched. In addition, seven-ply doors may have limited warranties.

Image courtesy of VT Industries, Inc.

Traditional five-ply doors are constructed with bonded core assembly using hot press technology. Manufacturers may offer two edge options: a compatible solid hardwood stile with exposed crossbands, or a compatible wood veneered or taped edge. Solid wood stiles are expensive and have the potential to warp and split. Also, the manufacturing process is not considered as environmentally friendly as the alternative veneered and hardwood edges because the natural resource is not fully utilized. Crossbands are exposed with the use of solid wood stiles, which create a less desired look. Wood tape edges are thin, which could lead to telegraphing issues, are easily damaged, and offer limited protection.

Source: VT Industries, Inc.

Advanced edge-before-face five-ply construction incorporates bonded core assembly construction with matching hardwood edges which are applied prior to the face material. This method eliminates unsightly crossbands and produces a seamless wood appearance. Matching hardwood edges provide design integrity and durability and all the materials meet industry performance standards for edge materials.