Underlying Factors to Consider in the Proper Specification of Carpet

Nov. 16, 2005

A beautiful commercial carpet installation relies on more than just a pretty face. It’s the underside that really counts. In a previous Fortune Contract white paper, the issues of fiber choices, dye methods, and texture options were discussed. This article addresses other important topics that affect the specification process, including primary and secondary backings, installation, and maintenance. These issues go beyond the design, color, and pattern concerns, yet can drastically impact the success of a project. A little knowledge about the variables in carpet construction below the face can be helpful.

Primary Backing
There are three main steps in the manufacturing process: dyeing, tufting, and finishing. Dye methods are explained in Specification of Carpet (another Fortune Contract white paper, available at www.fortunecarpet.com). Tufting is the process by which face yarn is sewn, or “tufted,” into a woven foundation or primary backing. In the center of the tufting machine, hundreds of threaded needles punch face yarn into the primary backing. This foundation is the source of stability for the carpet fabric throughout the entire life of the product. Primary backings are partially responsible for stability, pattern straightness, pattern clarity, and tuft bind in carpet fabrics.

Until about 1970, jute was the primary backing of choice. Today, most primary backings are made of polypropylene. Polypropylene doesn’t absorb water and greatly reduces the concerns associated with jute (shrinking, mildewing, rotting, and popping apart at the seams). The LEED Green Building Rating System® has brought interest back to jute as a rapidly renewable resource, but the polypropylene manufacturers have been proactive in adding post-consumer and post-industrial content to their products.

Pick count, or the number of threads per inch in the primary backing, is directly related to the overall dimensional stability of the fabric. Most broadloom commercial carpet uses a pick count ranging from 11 to 22 picks per inch. A primary backing with more picks per inch is inherently more stable than one with fewer. A more stable carpet translates to an easier installation with side match and bow and skew issues.

Secondary Backing
In the final stage of production, a secondary backing is adhered to the underside of the primary backing using an adhesive that is cured in an oven. The adhesive serves to provide dimensional stability and lock the face fibers into place. There are several types of backing systems with different characteristics to consider as they pertain to the end-use: performance, high comfort, noise reduction, rolling traffic, moisture barrier, and recycled content.

Most carpet is adhered with latex, a water-soluble adhesive. Latex is very serviceable in many applications. Over time, wet cleaning methods and humidity can break down the latex causing expansion, delamination, and wrinkling. Where moisture is an issue, it is more appropriate to specify a secondary backing that will perform in such conditions.

Performance backings are commonly made with polyurethane adhesive. Polyurethane backings come in many different thicknesses and densities that conform to the end-use requirements. With or without an attached cushion, polyurethane backings increase tuft-bind, help prevent edge-ravel, improve abrasion resistance, and offer a moisture barrier. With an attached cushion there are improvements in energy savings, ergonomic underfoot comfort, acoustical enhancement, rolling traffic mobility, and appearance retention.

The specification of high-density polyurethane with recycled content and a post-consumer recycled non-woven secondary backing fabric can contribute to the total building materials requirements for LEED certification. This is in addition to the point allowed for Green Label carpets certified by the Carpet and Rug Institute. You may also specify low-VOC emitting adhesives to be used and further contribute to LEED points.

So, your carpet textile has gone through the manufacturing processes. Just like other textile applications, the fabric must be pieced together to become a finished product. The quality is in the material itself, but the quality of assembly is equally important.

The satisfaction with an installation is largely based on the execution of seams. Seam placement is critical and should be addressed in the specification process. Properly placed seams run the length of an area, with - rather than across - traffic lanes. Lighting should not strike across a seam, as this will emphasize its appearance. Where possible, seams should not be placed at pivot points in traffic, and not perpendicular to doorway openings.

In addition to seam placement, examination of the carpet pile should be addressed. Carpet pile has a direction, like the nap of velvet or corduroy. The direction should remain consistent throughout an installation. Pile reversal will appear as shading, or a color variance, at the point where two widths of fabric meet.

Carpet with a specific pattern must be matched at the seams to have a satisfactory installation. Large patterns are easier to match but require more carpet. Smaller patterns are more difficult to match, and improper attention usually has unsightly results. Bow and skew are terms used to describe conditions that affect the ability to pattern match. Bow refers to when the pattern deviates in an arch toward the center of the carpet fabric. Skew refers to the pattern being square across the width. Most manufacturers have strict tolerances for these conditions, which typically occur during the finishing process. To correct many pattern-match issues, a qualified installer will use a power stretcher and stay nails.

Loop pile carpets, while generally considered more durable, are inherently more difficult to install. Careful attention must be paid to the use of seam sealers that permanently anchor the loops at the cut edge.

The Carpet and Rug Institute provides guidelines for proper installation in CRI-104 Standard for Installation of Commercial Carpets. It also certifies installers who follow its procedures. Part of the specification documents should state that these guidelines be followed, as well as those from the manufacturer.

Taking care of carpet after installation is important to the overall satisfaction with the performance and appearance retention of the textile. Lack of attention to maintenance issues will result in a shorter life-cycle for the carpet, as dirt will abrade the face fibers. Plus, improper cleaning can affect indoor air quality. In general, spots and spills should receive immediate attention, and cleaning should be scheduled and targeted to more heavily trafficked areas. Aggressive chemicals and methods should be used only with the appropriate carpet type. Most manufacturers provide cleaning and maintenance guidelines for their products. The CRI certifies cleaning companies and vacuum cleaners that have been tested to meet stringent criteria. Some observance of these guidelines should prolong the useful life of the carpet and contribute to a more healthy work environment.

Commercial carpet goes through many stages in manufacture. Beyond the surface, the underlying components can dramatically affect your satisfaction with a given project. Proper specification is about what’s “inside,” not just a pretty face.

To read this paper in its entirety, visit Fortune Contract

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