For glue-down installations where seams are involved, two or more breadths (panels) of carpet are dry fit and selvage edges are trimmed for a seam. Carpet is then folded or rolled along the length half the width. Adhesive is spread, allowed to “flash” and then a half breadth is laid into the adhesive. The seam is then sealed with either a universal acrylic, solvent type “honey” colored seam sealer, or a seam sealer recommended by the manufacturer. Once the first panel has been placed back into the adhesive, seam sealer is applied to the edge. This followed by laying the adjacent panel into the adhesive. The typical seam sealer bottle that is used to apply seam sealer is a plastic bottle with the tip cut at a slight angle (see Figure 1A). The adjacent panel is placed. Installers put the seam together by slightly lifting the edge so as to avoid adhesive and seam sealer from contaminating the face yarns of the second panel, net fit to the first panel then roll with the proper weight roller.
There have been some important changes to this process of preparing seams, the Carpet Rug Institute CRI 104 now states. 13.5 Seam Adhesive (“Sealer”) - For carpet systems that require seam sealing, apply an appropriate seam adhesive in sufficient quantity to seal both edges trimmed for seaming, covering the thickness of the primary and secondary backing without contaminating face yarns (see Figure 1). This insures that all edges trimmed for seaming are protected from edge ravel. Allow seam adhesive to dry before proceeding with the installation to prevent transfer to the face yarn. An additional bead of seam adhesive is applied to the cut edge of one side only, after that side is first placed into the floor adhesive. In order to weld the seam edges together, while the seam adhesive is still transferrable, abut the edges to form the seam.
Note that the CRI now recommends a double sealing system versus the 1/8” bead application on one side that was recommended for years. One concern with only sealing one time and on one side of the seam is when an installer uses a solvent type of seam adhesive. Multipurpose adhesive, which is water based, is not compatible with oil/solvent-based seam sealers. When placing the second panel to fit at the seam, many installers tend to slide the second panel into the multipurpose and the solvent based seam sealer, causing contamination at the seam. The seam is sealed and will probably maintain its integrity for a while but given time, where the contamination occurred, the potential for seam failure increases. If hot water extraction is used, the surfactants (soap) can potentially start to break down the multipurpose adhesive where it contaminated the seam creating a weaker seam. This is another reason not to rely on multi-purpose adhesive as a seam sealer.
When using a universal acrylic seam sealer, even though it is water based just as the multi-purpose adhesive, there are different properties. Acrylic seam sealers dry harder while multi-purpose stays fairly pliable. So, even though they are both water based there are differences and cross contamination can still be an issue.
A typical application of seam sealer is where the installer or apprentice seals the entire length of the seam and then the installer will work the seam together. Ever see a seam failure where the installer used a seam sealer and the secondary backing is adhered to the substrate yet, the primary backing and tufts delaminated? Inspect to see if seam sealer is underneath the secondary backing. It could very well be that the seam sealer flattened out which would explain why the secondary backing is adhered so well. The viscosity of the seam sealer can make a difference. A low viscosity seam sealer (runny) will not maintain the 1/8” bead that the industry/manufacturer requires. Remember, seam sealer is designed to seal the edge between the primary and secondary backing. So how does an installer create a properly sealed seam? When applying seam sealers, only apply a few feet in front of you as you are putting the seam together, this will minimize the flow out of the seam sealer. Try not to slide the second piece of carpet in the multi-purpose adhesive when constructing the seam to avoid contamination.
Photos 3 and 4 show a seam sealer bottle specifically designed for sealing glue-down installations. The red tip bottle is used for standard backings while the black tip (Photo 5) is used for attached cushion installations. The bottle is placed into the seam between the two panels and the installer pulls and squeezes the bottle.
Carpet with an attached cushion also requires seam sealing but not with the typical squeeze bottle that is used. Many installers either don’t seal or improperly seal cushion back carpet. The seam sealer is not applied at the base of the attached cushion but applied at the point where the carpet and attached cushion are bonded.
In Photos 8 and 9, can you see where the seam sealer should be applied? Definitely not at the base of the attached cushion. You can also see that this edge was not sealed with seam sealer.
Note: Seam sealer bottles courtesy of Beno J. Gundlach.