All things Gypsum: Application of Gypsum Panel
June 25, 2008
Products over Existing Interior Walls and CeilingsThis column was originally run in October 2004 when home-owners were fixing up older homes in hopes of flipping them for a handsome profit. Now that the housing market is experiencing a correction in much of the country, more homeowners are staying put and sprucing up their homes with the intent of upgrading without having to sell in a soft market. We’ve made a few tweaks to the article since it was originally run to make it more timely but the information herein is as valuable now as it was then, if not more so.
A trend in this series of articles has been to focus on new construction, and to address some of the more common-and in some cases less common-situations encountered by drywall contracting companies of medium to large size. Consequently, little attention has been paid to the procedures used in renovation projects, where modifying the existing construction is frequently performed by the smaller contractor.
One of the potential problems with an older home, particularly one with lath and plaster walls, is that the plaster may be in less than ideal condition. Occasionally the topcoat has begun to delaminate from the base coat, and in some instances the base coat has begun to let go of the lath. Unfortunately, plaster repair has become a very specialized trade, and in many areas it is becoming increasingly difficult to find a contractor who can do these repairs on short notice.
It is often more practical and cost effective to use gypsum panel products to repair or resurface walls that are unacceptable in appearance or to cover unwanted openings. However, because this isn’t new work, there are some situations that may emerge that will challenge the renovator, and if not executed properly, will produce aesthetically unpleasant or unacceptable results. Section 12 in GA-216, Application and Finishing of Gypsum Panel Products, addresses items that make the difference between a poorly done renovation using gypsum panel products versus a well done one.
These points may seem quite obvious; however, sometimes the urge to skip certain steps may outweigh the concern that the job won’t turn out as well as it should-that only the trained eye would see any imperfections, and most homeowners just aren’t that discerning. Most of us who’ve attempted this kind of work and succumbed to this line of thinking have suffered the consequences and wound up learning the hard way that it is better (and far more profitable) to do it right the first time.
Section 12 of GA-216 offers direction on proper surface preparation, framing spacing, furring, fastener spacing, shimming and adhesive attachment. Most of these recommendations are relatively simple, but followed in their entirety and in the proper sequence can make a significant difference in an overall project’s final appearance. Here are the highlights in narrative form:
The preparation for renovation or remodeling work with gypsum panel products lays the foundation for the rest of the work. If the preparation is substandard, the final product is going to suffer. GA-216 recommends that wall and ceiling surfaces must first have all wallpaper and loose plaster removed, high spots shaved down, and low spots filled before receiving additional layers of gypsum panel products. Voids resulting from the removal of loose plaster must be shimmed to the same thickness as the plaster prior to installing new gypsum panel products. As an alternative, the entire area to be repaired can be furred out. In the instance where more than 50 percent of the wall or ceiling surface is damaged or removed during the renovation process, the entire surface must be removed and the gypsum panel products applied over the existing framing as if for new construction.
As mentioned above, areas where the existing plaster has been removed down to the lath or other substrate must be shimmed so that the shims are flush with the surrounding plaster to ensure that the gypsum panel products placed over the area are installed without protruding edges. Wood shims must be a minimum of 1½ inches wide (the same width as the narrow dimension of a nominal 2x4), and gypsum panel shims must be a minimum of 2 inches wide. It is important that the shims comply with the minimum width requirements because if there is a butt joint in the wallboard, there must be sufficient shim material beneath to properly support the ends of both boards. Also, if the wood shims are too narrow, they are more likely to split when attempting to run a fastener through them. Fasteners (nails or screws) must be spaced no more than 6 inches on center when attaching shims to either wood or steel framing.
To prepare for the installation of furring, bulges in the existing surface that prevent the furring from fitting tightly against the surface must be removed. This will allow the face of the furring to be placed level across the wall or ceiling. Shims are to be used to level the surface of the furring where voids or depressions occur in the surface of the substrate.
It is important to determine the condition and spacing of the existing framing before applying a layer of a gypsum panel product to an existing wall even if the framing members are covered by a finish material, such as plaster or gypsum board. Gypsum panel products may be applied directly to existing wall and ceiling surfaces using nails or screws alone, or in combination with supplemental adhesives. When doing so, it is important to ensure that the framing members are sound, rigid, and properly aligned. Framing should not be spaced more than 16 inches on center for 3/8-inch thick gypsum panel products or not more than 24 inches on center for ½-inch or 5/8-inch thick gypsum panel products. Gypsum panel products that are either ¼ inch or 5/16 inch thick should only be used for direct application to mechanically sound walls and ceilings that are flat, level, and without void spaces.
Nails and screws may be used to apply gypsum panel products over wood-framed walls; steel-framed walls always require the use of screws. Whichever fastener is being used, one must ensure that the fastener length is sufficient to penetrate through the new gypsum panel product and the existing finish to the required depth into the framing. Nails must penetrate into wood framing at least 7/8 of an inch. They must be spaced no more than 8 inches apart on walls and no more than 7 inches apart on ceilings.
Screws must penetrate into wood framing at least 5/8 inches and into steel framing at least 3/8 inches. Screws must not be spaced more than 16 inches apart on walls and 12 inches apart on ceilings where framing members are spaced at 16 inches on center. Screws must be spaced no more than 12 inches apart on walls and ceilings where framing members are spaced at 24 inches on center.
Adhesive may be used to enhance a fastener attachment of gypsum panel products to plaster walls or existing or new framing members. Before using an adhesive to install gypsum panel products to an existing surface, bond tests on the existing substrate should be conducted in several areas to ensure the effectiveness of the system. To test the bond of an adhesive, remove any loose material or wallpaper from the plaster so that the adhesive used is in direct contact with a mechanically sound surface. Apply a single 3/8-inch by 3-inch bead of adhesive to an 8-inch square sample of the gypsum panel product and press the sample to the surface. Repeat this process in several areas throughout the project. Allow the adhesive sufficient time to set (per the label directions) and then evaluate the bond by pulling the samples away from the existing surface. The bond is considered acceptable if the backing is torn from the specimens and remains attached to the wall or ceiling. If the bond is determined to be acceptable, the gypsum panel products may be applied to the existing plaster surfaces using a combination of fasteners and adhesive as shown in the table below.
Installing a new gypsum panel product surface over an old wall or ceiling is often the best way to revitalize an existing room. It is usually faster, cheaper, and requires skills that are more readily available and more easily acquired than those needed for replacing or repairing large areas of damaged plaster or gypsum board. Anyone who can competently install and finish gypsum panel products can take advantage of the growing repair and remodel market with excellent results by applying the practices described in GA-216, Application and Finishing of Gypsum Panel Products. W&C