Section V – Joint and Fastener Treatment

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V. JOINT AND FASTENER TREATMENT

After installing and securing the gypsum board with the proper fasteners, one must reinforce and conceal the joints, fastener heads, and corner beads. Use joint compound and joint tape that conform to ASTM C 475 “Standard Specifications for Joint Treatment Materials for Gypsum Wallboard Construction” for this stage of the process. Ensure that all compounds used are compatible. Do not mix different formulations unless recommended by the joint compound manufacturer. During the taping and finishing operations, provide adequate and continuous ventilation to ensure proper setting and drying of the taping and finishing compounds. Use pre-creased tape the corners of wall and ceiling intersections. Use metal or plastic casing or trim to conceal exposed edges of the gypsum board.

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Photo of 2-Story Entry Way With Wallboard Joints and Fasteners Covered with Joint Compound

Fig. 35 – Gypsum Board Walls and Ceilings with Joints Treated to Give Monolithic Appearance

Cross Section Showing Layers of Taped Wallboard Joint

Fig. 36 – Cross Section Showing Layers of Taped Gypsum Wallboard Joint

Applying Bedding Coat of Joint Compound

Fig. 37 – Bedding Compound Being Applied

Embedding Tape in Compound 

Fig. 38 – Joint Tape Being Embedded into Compound

Applying Additional Coat of Compound over Joint

Fig. 39 – Joint Topping Applied

Applying Tape and Joint Compound with Pneumatic Machine

 

Original photo courtesy of AWCI

 

Fig. 40 – Machine Application of Tape and Compound

EZ PRO Spray Texture

Original Photo Courtesy of EZ PRO

 

Fig. 41 – Spray Applying Texture

Joint Treatment Products and Precautions

Joint tapes work with ready-mixed or dry, powder-type joint compounds to reinforce and finish the joints between adjacent gypsum boards. Paper tape with metal strips is available to reinforce exterior corners.

Joint reinforcing compounds are of three general types:

1. A taping or bedding compound used to attach the tape to board

2. A finishing or topping compound used especially for finishing

3. An all-purpose compound to be used for both embedding and finishing.

Most ready-mixed joint compounds contain water-soluble organic thickeners and adhesives or synthetic resins. These products achieve their strength and adhesion through drying and are consequently referred to as “drying compounds.” The loss of water inherent in drying compounds results in shrinkage, which necessitates several thin applications of the compound. Each application must dry thoroughly before the next application is started to ensure the desired result. Synthetic resin compounds such as “vinyls” will keep longer than the organic water-soluble types. Ready-mixed joint compounds come in two consistencies: one for hand application and the other for machine application.

Another family of joint compounds achieves strength by setting and is referred to as “setting type” joint compounds. These products are dry powders that must be mixed with water. To meet varying job requirements, setting type joint compounds come in a wide choice of setting times. The set may occur within 5 minutes or take as long as several hours. Setting compounds are formulated with specific setting-time ranges and must be used within those prescribed time limits. (Additional coats are possible before complete drying takes place.) A common practice is to use setting compounds for embedding the tape and “non-setting, or drying,” types for the finishing operation.

Do not allow ready-mixed compounds to freeze. Do not begin taping and finishing operations until the interior temperature has been maintained at a minimum of 50 degrees F for a period of at least 48 hours. Maintain the minimum interior temperature until the compounds have completely dried. Note: Kerosene and propane heaters emit unacceptably high levels of moisture for the proper drying of non-setting type joint compounds. Avoid using any heater that burns petroleum products or gas to achieve the minimum interior temperature while working with non-setting type joint compounds.

Avoid contaminating containers or tools used for different types of joint compounds when mixing or storing. Even a small quantity of one type of joint compound in the seam of a mixing pail or inside a pump or on a tool can adversely affect the adhesive properties of a full mixture of another type of compound. All equipment must be clean: disassemble and clean all tools after each use.

Always wear an approved protective respirator when mixing powder or sanding dry compound. Always mix materials per the manufacturer’s directions.

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Joint Treatment Procedure

Pre-fill any gaps between gypsum boards that exceed 1/4-inch with setting-type compound prior to commencing the taping process.

Fill the depression formed by the tapered edges where gypsum boards join with taping or all-purpose joint compound. Do not use topping or finishing compound for embedding tape. Wipe off excess compound that is applied beyond the groove. Center reinforcing tape and press it down into the joint compound with a 4 -inch broad knife or smooth-edged trowel. Draw knife along joint with sufficient pressure to remove excess compound above, below, and along edges of the tape. Leave sufficient compound under tape for a proper bond but not more than 1/32 -inch under the feathered edge of the tape. Take care to leave a thin coat of joint compound over the embedded tape, as it reduces edge wrinkling or curling and makes the tape easier to conceal with following coats. (The initial tape embedding can also be done with a semi-automatic tool that applies the joint compound and tape simultaneously.) Allow the compound to dry completely. Drying can take 24 hours or more, depending on temperature and humidity.

After the embedding coat is completely dry, apply a second coat of topping or all-purpose joint compound feathered about two inches beyond edges of the first coat. Spot fastener heads and allow to dry.

After the second coat is dry sand lightly, if necessary, or wipe with a damp sponge and apply a thin finishing coat to joints and fastener heads; use topping or all-purpose joint compound. Feather edges to at least 6 inches on each side of the joint. The final step prior to decoration is to lightly sand the joints in order to eliminate laps where joints intersect and in general to smooth the surface where necessary. Take care to avoid scuffing the paper surface of the gypsum board, as the scuffed areas may be visible after the decoration. Back-fill all cut-outs with compound used for taping or finishing so that there is no opening larger than 1/8 -inch between the gypsum board and a fixture or receptor.

At joints where there are no tapered edges, such as where two horizontal square-cut edges meet together, additional care is necessary to make the joint look as monolithic as possible and create the “illusion” of

smoothness. Fill the area where the boards meet with taping or all-purpose joint compound. (Do not use topping or finishing compound for embedding the tape.) Center the reinforcing tape and press it down into the joint compound with a 6-inch broad knife or smooth-edged trowel. Draw knife along joint with sufficient pressure to remove excess compound above, below, and along edges of the tape. Leave sufficient compound under tape for a proper bond but not more than 1/32 -inch under the feathered edge of the tape. Take care to leave a thin coat of joint compound over the embedded tape, as it reduces edge wrinkling or curling and makes the tape easier to conceal with following coats. (The initial tape embedding can also be done with a semi-automatic tool that applies the joint compound and tape simultaneously.) Allow the compound to dry completely. Drying can take 24 hours or more, depending on temperature and humidity.

After the embedding coat is completely dry, apply a second coat of topping or all-purpose joint compound over the tape with a 10-inch knife or trowel. Apply two wider stripes of compound along the side of the tape to create a significantly wider joint. Feather edges to approximately 18 – 24 inches.

After the second coat is dry sand lightly, if necessary, or wipe with a damp sponge and apply a thin finishing coat to joints and fastener heads; use topping or all-purpose joint compound. Feather edges to at least 12 inches on each side of the joint. The final step prior to decoration is to lightly sand the joints in order to eliminate laps where joints intersect and in general to smooth the surface where necessary. Take care to avoid scuffing the paper surface of the gypsum board, as the scuffed areas may be visible after the decoration.

While joints are being finished, fastener heads should also be spotted with compound. Apply compound with a 4-inch knife to fill depressions created when fasteners were set slightly below the board surface.

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Texturing

Decorators and design professionals routinely specify texture finishes for gypsum board surfaces. There are many choices of commercially available texture finishes compatible with gypsum board, ranging from light stipples to heavy swirls or simulated acoustical finishes. These finishes are typically machine applied; however, certain finishes can be brush-and-roller applied, while others require specialized hand tools. In all cases, such finishes perform best when applied over a sealed or primed gypsum board surface. Always prime or seal bare gypsum board surfaces with a product recommended by the manufacturer of the specified texture product. Unless specifically recommended, do not use stain-blocking, fast-dry primers directly under texture products, as those primer products generally lack sufficient profile and absorption properties to properly bond with the finish

product.

Texture finishes are not generally considered final finished surfaces. They must be over-painted when thoroughly dry with a primer or finish paint applied according to manufacturers recommendations.

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Trim and Casings

Figure 42 illustrates some of the more common sections used around doors, windows, and other openings. They are also used when gypsum board is butted against a different surfacing material.

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Diagram of Different Corner Beads

Fig. 42 – Examples of Corner Bead, Trim, and Casings

Perimeter Relief

Detailed designs for perimeter relief of nonbearing partitions are available to improve this condition (Fig. 43). The use of relief runners to attach nonbearing walls to ceiling and column members is effective in the prevention of cracking due to structural movement.

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Diagrams of Perimeter Relief Assemblies

Fig. 43 – Examples of Perimeter Relief Assemblies

Detail of Control Joints

Detail of Control Joint

Fig. 44 – Details of Control Joints