Carpet Specification

Nov 1, 1998 12:00 PM

Certain issues need to be addressed in order to specify carpet, regardless of the type of installation site. The specifier needs to determine the expectation for the carpet and which of the selection criteria are most important. The following basic issues should be considered to determine carpet specification:

-Aesthetics: color, texture, design/pattern, luster and appearance.

-Appearance: durability, wearability, cleanability, installability, color retention and fastness, texture retention, appearance retention, etc.

-Functionality: flammability, static propensity, indoor air quality, acoustical value, insulation, value, etc.

-Cost: initial product cost, installation, maintenance, disposal, life cycle.

-Government or building code requirements.

There are two types of carpet specifications: construction and performance. Construction specifications tell the manufacturer in very precise terms how the carpet is to be made (look, size, weight and manufacturing of raw materials and processes) without directly stipulating performance needs or end-use requirements. A construction specification would include the following:

-Construction type: tufted, woven, knitted, needlepunched, etc.

-Construction materials: fiber (fiber type, size), backing (type, weight) and adhesives.

-Construction methods: yarn manufacturing (yarn size and ply), fabric formation (gauge, pile height and texture, density, total weight), coloration techniques (dyeing methods), finishing and treatments.

-Product characteristics: texture, color/design, size/type and functional enhancements.

Common errors in construction specifications are either to under- or over-specify. When too many minor details are included, there is a tendency to specify beyond the possibilities of the manufacturer or to limit the flexibility of new technology. The specification for yarn size might be too large for a particular gauge, or the yarn size, gauge, stitch, pile height and weight might be impossible to create in the specified combination. There also is a tendency to perceive that more is better-more pile weight, more plies, more rows, etc., mean better durability. Each of these does play a role, but the "more" perception may not relate to better performance or product.

Another consideration is that with current manufacturing technology and anticipated technological developments, many of the standard terms may not apply today. For instance, air-entangled yarns are really not plied; therefore, twist per inch does not have the same meaning as for twisted yarn. Scrolling, shifting, eccentric or pattern tufting machines provide mixed gauges and stitches and, with overtufting, even changing gauges.

Construction specifications should be used to describe the overall look of a product and not be so detailed as to limit the manufacturer from making a quality product.

Important factors One of the most important, and often most misunderstood, factors in a construction specification is density. Density is simply the index of how much yarn is packed into a given volume or area. The larger the density value, the more compact the pile, which yields a firm walking surface.

Density can be an important determinant of carpet performance-especially for high-traffic environments. Density is influenced by many factors, such as stitches per inch, yarn thickness, gauge and tuft height. Gauge is more a function of yarn size: a "fat" or larger size can be tufted at a wider gauge, or smaller yarns at a tighter gauge, and receive the same density rating. Specifiers who understand the various factors affecting density have a greater chance of specifying the best carpet performance for a given budget.

There are various methods of stating relative density specification for pile carpet. Average pile yarn density (APYD) is the most common and useful decision tool used in conjunction with other carpet specifications. It is determined by pile weight (specified in finished ounces per square yard), pile thickness or tuft height. Pile thickness and tuft height are laboratory means ofdetermining what is commonly known as pile height. Pile height is sometimes measured with a small ruler or dipstick, but these only make rough determinations and should not be considered accurate.

Note that while other approaches quantify density, APYD usually is adequate. Generally, the higher the APYD value, the better the expected carpet performance, once other important factors are considered. Average pile yarn density for quality commercial carpet will normally exceed 4,000, while high-demand usage may require an APYD of more than 6,000. Other factors indirectly help determine density, such as the number of tufted rows across a unit width and the number of stitches per unit length of each tuft row.

In tufted carpet, gauge, or the reciprocal of the number of tuft rows per inch of width, is a major density factor. For example, a 1/8-gauge carpet has eight tuft rows per inch of width and a 5/32-gauge carpet has 6.4 rows per inch of width.

When comparing density, look at the whole picture. In theory, a 1/8-gauge carpet should be more dense than a 5/32-gauge carpet. However, other factors, such as yarn size and pile thickness, come into play and will have a great effect on the pile density of the product.

For woven carpet, the equivalent of gauge may be obtained by dividing the pitch (number of ends of yarn in 27 inches of width) by 27 inches.

The number of stitches (tufts) per running inch of carpet usually is specified directly for tufted carpet, but is called rows per inch for woven carpet. The numerical product of tuft rows per inch of width multiplied by stitches per running inch is the number of tufts per square inch, or tuft density.

Additional factors Other factors that affect carpet performance include yarn size and characteristics. Yarn twist and proper heat setting are of utmost importance for cut-pile styles. A low twist, or poorly heat-set yarn in a cut-pile carpet will tend to mat, tangle and appear worn.

Other quality determinants often written into construction specifications are the backing systems used, the type of fiber, whether the yarn is spun or continuous filament, and the dye method used.

Although not considered descriptive of quality or performance, total finished carpet weight is sometimes included in specifications. It should not be confused with pile yarn weight. Total finished weight includes all backing materials, latex, foams, topical finishes and face yarns. Like pile yarn weight, total finished carpet weight is expressed in ounces per square yard. It is primarily used as an indication of roll weights.

Construction specifications can be proprietary, identifying a specific carpet by grade, name and manufacturer. An "or equal" specification also could identify a specific grade, listing its construction factors so that other manufacturers can bid for the order competitively. In this case, the usual procedure is to approve "or equals" in advance of the actual bidding. Full attention then can be given to price and delivery information when bids are analyzed.

Avoid over-specifying. As new technologies emerge, construction specifications will become less important, especially as performance estimators. Appearance is simply an aesthetic choice, while appearance retention truly is a performance issue. Therefore, performance specifications will likely increase in the future.

Performance specifications Performance specifications detail the necessary performance attributes, telling the manufacturer how the carpet must perform without detailing how it must be made. Specifying performance rather than construction can take the difficult pressures off the specifier to provide accurate details and is safer for the specifier who is not familiar with the latest carpet technology and materials.

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