New Gypsum Board in General

For a while now, there has been a lack of understanding of the issues and concerns that come between the industry trades of gypsum board finishing, paint and wallcovering application and what is stated in the project specifications. This lack of understanding leads to finger-pointing whenever performance expectations are not met.

A Comprehensive Guide to Painting & Finishing Interior Gypsum Part I

Environmental Control

The potential for finishing and decorating problems are minimized when temperature, humidity, and airflow remain constant and as close to occupancy environmental conditions as possible. A minimum temperature of 50°F (10°C) and a relative humidity of 25% to 60% should be maintained continuously for 48 hours prior to and throughout the finishing process until applied materials are thoroughly dry.  It is recommended that the temperature and humidity be maintained at levels close to occupancy until the construction is complete and the building is occupied. Keeping the humidity and temperature levels maintained will help with thermal movement within the wall and ceiling surfaces. It is recommended that this requirement be included in the project specifications under the general contractor’s responsibility.


Accessories come in a wide range of shapes and sizes for a variety of uses with gypsum board. They include termination, decorations, corner reinforcement, material transition, reveals, coves and many other items.


Due to the gypsum board finishing process, the abutting gypsum board seams/joints, fasteners, and accessories must be concealed with fill and finish coats of joint compound.  It is not possible to achieve a finish surface that is a flat plane.  This gypsum board finishing process occurs above the plane of the gypsum board.  Achieving proper concealment involves finishing the joints and fasteners in gradual arcs that minimize recesses and/or ridges that would otherwise remain visible.

The transition from joint compound to gypsum board and/or accessories will be finished to have a smooth surface, not necessarily flat.  Again, the smooth surface in this “Guide” is describing the transition, not a flat or a machined finish/surface

Here are some other items that affect the flatness of gypsum board. Gypsum board is a panel product. The plane and alignment of the panels depend on the plane and alignment of the framing members, backing or devices to which it is attached, and/or conceals.

The tolerance of 1/8” in 10’-0” is commonly used in jobsite specifications and referred to as the “industry standard” for flatness in gypsum board finishing. However this tolerance was originally created for wood framing.  It was established to help minimize the use of twisted or bowed lumber that would typically cause issues later in the project.   Keep in mind, in wood framing the top and sill plates are the same width dimension as the framing members. Blocking is able to be inset of the framing members with fasteners (typically nails) that are driven flush, eliminating flatness issues.

This “Interior Guide” is to serve as a guideline and is not intended for any specific construction project. This “Interior Guide” makes no warranty, guarantee, expressed or implied. This is considered to be a “living document” and is subject to be edited, updated and or removed at the discretion of “advisory committee” without notice. The most updated version will be on the WCC website ( Please reference the website as needed to ensure you have the most recent version.

This 1/8” in 10’-0” has carried over into metal stud framing.  The 1/8” in 10’-0” tolerance should be used for vertical alignment (plumb) of the metal studs only (excluding the track and screws).  Metal stud framing is typically installed well within this tolerance.  Concerns become relevant when backing is introduced to the framing or when the wall is checked for flatness or plumb over backing, screws, track and/or accessories.

Here are some items that typically create issues with the flatness criteria:

 Metal Track – This item is fabricated to fit around the framing member.  Depending on the mil (gauge) thickness of the track, it can provide an additional thickness of 3/32” on each side of the framing member (3/16” overall).

 Screws – Truss and Pan Head-type (non bugle) fasteners can have fastener heads that measure 3/32” in thickness and greater.  Adding the thickness of the fastener head to the track thickness, the buildup can be 3/16” and greater above the face of the framing members.

 Backing – Backing is typically detailed to be applied onto the face of the framing members.  All of this thickness is outward of the face of the framing member.

 Accessories – Control joints, corner beads, “L” moldings etc. are considered accessories.  These accessories are created with a joint compound gap (allows joint compound to fill and cover the attachment flange) with a screed edge that is 1/32” to 1/16” above the finish accessory creating a smooth (not flat) transition.

When all of the above items are compounded, along with the finishing (fill and finish method) of flat joint(s) and angles into an assembly, it should be understood why a flatness tolerance is unachievable.  It should also be understood this variation typically has nothing to do with the installation or workmanship. Rather, it’s the result of the products used in the designed assembly.

Critical Lighting

Critical lighting refers to a surface that is illuminated or flooded with artificial and/or natural light. Critical lighting, such as strong oblique light from windows or surface-mounted light fixtures, will exaggerate minor surface differences. Where critical lighting cannot be avoided, the effects can be minimized by either skim coating the entire wall or ceiling surface, decorating the surface with medium to heavy textures, or using draperies and blinds. In general, non-flat and dark/deep tone paints highlight minor surface differences, whereas textures and flat paints conceal minor differences.

Joint Photographing

Joint photographing is an occurrence where the finished joint areas shadow through the surface decoration.  Joint photographing is usually only visible when viewed at an angle or under side lighting. The cause is either a texture or a porosity variation between the joint compound and the face paper of the gypsum board.


A mock-up should be specified in the jobsite specifications for three critical reasons;

 To determine whether the project specifications, industry/manufacturer’s recommendations, and workmanship are collectively appropriate for the selected location within the structure.

 To determine if the desired final appearance is achieved. Once completed, the mockup shall be accepted by the design professional, owner, contractor(s) and or any other interested party prior   to beginning any widespread finish work.

 To illustrate what the durability (softness, adhesion, etc.) of the completed surface before widespread work is completed.

It is recommended that the mock-up shall be of sufficient size to represent the requirements of the jobsite specifications that may include, but are not limited to, Gypsum Board Levels of Finish, accessories, texture, paint, wallcovering, trim, lighting (natural or artificial), etc. An approved mock-up may become part of the completed work if undisturbed at time of substantial completion of the building. Whenever additional measures are required and approved outside of the jobsite specifications, project documents should be amended accordingly and additional compensation approved.

Drywall Primer/Drywall Completion Coat

The term “Drywall Primer” has brought confusion to the gypsum board and painting industries for quite some time for the reasoning of “what is it” and “who applies it”.

What is it” – Drywall primer is typically a paint material that is formulated to be applied directly over newly treated gypsum board and joint compound.  There are different types of drywall primer(s) on the market.  The question is what are the expectations of the drywall primer?

If the expectation of the drywall primer is to enhance the following coat of paint and help seal the surface, then a PVA (poly vinyl acetate) type drywall primer is recommended to be specified. This type of drywall primer is designed to be applied as a thin film coating 4.0 mils WFT (no less than 2.0 mils DFT) and it does not help with the texture difference that occurs in Gypsum Board Levels 3 and 4 Finishes.

If the expectation of the drywall primer is to enhance the gypsum board surface, then a priming material known as a drywall completion coat is recommended to be specified. A drywall completion coat is typically not classified as a paint material, it’s designed to be applied from 6.0 to 12.0 mils WFT (4.0 to 9.0 mils DFT) or (2 separate coats at 5 mils WFT, this reduces moisture issues).  It’s formulated not to seal the surface, but to create a film solid that helps provide consistence with the porosity over the gypsum board surface and joint compound, this film solid also helps minimize the texture differences that occur in Gypsum Board Levels 3 and 4 Finishes.

Who applies it” – Some feel that because the term drywall primer is referenced in the ASTM and the GA standards in the gypsum board sections that it is a material for which the gypsum board finishing contractor is responsible. Others feel that since drywall primer is classified as a paint material, the painting contractor is responsible for it.

The first step is to determine which type of product is going to be used. This helps decide which trade may or can apply this material. Typically if a drywall primer is the material of choice, the painting contractor usually has the responsibility of application. However, if the priming material is a drywall completion coat of choice, the application responsibility can be either in the painting contract or in the gypsum board contract. The project specifications need to direct which trade (painting or gypsum board finishing) will apply what product.

Since the architect/designer knows what appearance or performance they are expecting from the final decoration, they shall specify which product is to be used and which workforce shall apply it.

With certain final decoration systems, a drywall primer (PVA or a sealer type) may need to be applied over a drywall completion coat to help with angular sheen porosity.  Where additional finishing is required to correct defects found in the surface after the application of either type of primer, a recoat (additional coat) of the primer shall be applied to the affected areas after the additional finishing is completed.  It should be understood that the application of any primer or priming material is not a requirement of the last application or step for Gypsum Board Levels 3, 4 and/or 5 Finishes.

Fuzzed Paper

This is the area of the gypsum board face paper that has been touched, glazed, sanded or wiped with either sandpaper or a trowel. Due to the applications or sanding of the joint compound, the face of the gypsum board is used as a guide to which to finish or sand to, and this area becomes worn and can raise the nap of the face paper.  Care shall always be exercised to ensure that the nap of the face paper of the gypsum board does not become damaged. The raised nap face paper can become magnified when incorrect primer/sealers are applied or when primers are spray-applied and not back roll(ed) over the surface. Note: a drywall completion coat material or a skim coat can help minimize fuzzed paper.


Select sandpaper, sanding film, and/or abrasive mesh with grit as fine as possible which still allows for an acceptable sanding rate.  Use caution when sanding to minimize sanding marks that may remain visible after painting.  Care shall be exercised to ensure that the nap of the gypsum board face paper is not raised during sanding operations.

Skim Coat

This is the final application or step in a Gypsum Board Level 5 Finish. A skim coat is essentially a film of joint compound or manufactured material designed especially for this purpose and that is applied over the entire surface. A traditional skim coat is described as having a trowel consistency with the intent being that the viscosity of the joint compound be such that it can be applied by a trowel. Other tools may be used for application so long as the trowel consistency is achieved. A manufactured material skim coat shall be applied following the requirements of application and tools

The objective of the application is to achieve total coverage of the entire surface with the skim coat. This can be accomplished by delivering the compound or material to the surface using a broad knife, roller, spray or per manufacturer’s recommendations.  Once applied, the excess joint compound is immediately sheared from the surface for traditional skim coat applications.  The manufactured material shall be applied and finished per manufacturer’s recommendations.

The intent of the skim coat is to conceal minor surface differences, minimize fuzzed paper and texture differences while providing a more uniform surface to which the final decoration can be applied.

Keep in mind, there is no specific mil thickness that constitutes a proper skim coat for a traditional application.  A skim coat will not approximate a plastered surface. Once the skim coat dries and has been sanded, the gypsum panel surface may show through and the treated joints, filled voids, and spotted fastener heads will likely be visible and the porosity may still vary.


The transition from joint compound to gypsum board and/or accessories can achieve a smooth surface by lightly sanding. Smooth surface in this “Interior Guide” is describing the transition (feel/appearance), not a flat or a machine finish/surface. It is not possible to achieve a finish surface that is a flat plane; due to the gypsum panel finishing process occurs above the plane of the gypsum panels.  Depending on the application of the material, the surface may have a slight texture finish.


Texture material can be applied by brush, roller, spray, or trowel, or a combination of these tools, to create the desired effect. A material (pre-texture material, drywall primer or application of joint compound) shall be applied to the surface prior to texture. This material shall be formulated to minimize the porosity difference across the surface and shall be applied by the trade responsible for applying the texture. Textured wall surfaces are normally painted with a protective paint coating after installation. Consult the texture material manufacturer for specific recommendations.

Note: A non-continuous texture is a pattern where a portion of the panel surface remains exposed after application.

This “Interior Guide” is to serve as a guideline and is not intended for any specific construction project. This “Interior Guide” makes no warranty, guarantee, expressed or implied. This is considered to be a “living document” and is subject to be edited, updated and or removed at the discretion of the “advisory committee” without notice. The most updated version will be on the WCC website ( Please reference the website as needed to ensure you have the most recent version.

Source: The Interior Guide

PPT will continue with Part II – A Comprehensive Guide to Painting & Finishing Interior Gypsum

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