In the last issue we discussed carpet construction and face styles and how they contribute to performance or the lack thereof. Next we’ll look at backing systems, their importance, influence and how they affect the carpet and its performance.
I have often said that the most important part of the carpet is the backing, it’s the foundation for a perfect installation. The backing offers support, dimensional stability and structural integrity. Specialty backings offer a moisture barrier, cushioning, anti-microbial properties, adhesion and pliability. Specialty primary backings guide pattern alignment and assist in anchoring yarn tufts. There is so much new technology in carpet backings that it’s challenging to stay on top of it all.
Some of this technology is not even in use yet, and I can tell you this with a modicum of certainty, when it comes on line it will revolutionize the installation process. The industry is hard pressed to adapt all of the changes occurring in carpet backings but change it will, inevitably.
Primary Backings:
Most primary backings for tufted carpets are woven slit film polypropylene although some nonwovens are used for special applications. More and more specialty primary backings, such as SI Flooring Systems Pattern Lok, are being used in commercial carpet with all of the pattern product being sold. These backings are new to the industry and already improvements on the original designs are being implemented such as the elimination of tufting needle deflection. Another consideration of primary backings is the amount of dimensional stability they lend to the product. This is especially important with pattern goods because the finishing process has the greatest tendency to cause bow, skew and waver in the pattern. The more stable and straight the product can be held while it’s being processed, the less challenging the installation procedure is going to be and the fewer the headaches for the commercial manufacturer and flooring contractor. Whatever the backing costs it’s cheaper than all the other expenses related to patterns that go in every direction but straight which then generate complaints, claims and profit losses.
Between the primary and secondary backings is where the moisture barrier materials will be placed and located. This barrier will prevent moisture from going through to the carpet backing preventing all kinds of things from happening including mold and mildew growth, bacteria, odors, delamination and adhesive failure. It is important to understand however that when moisture is not getting through from the top down it may also be prevented from getting from the bottom up. If that should be the case where substrate moisture vapor emission is an issue, the installation could be compromised. No matter who you are in the industry, manufacturer or flooring contractor, you have to ask about the permeability of the backing from the top down and from the bottom up.
Woven goods combine the face yarns into the backing of the product. There is no separate primary and secondary backing unless a specialty secondary backing is specified.
PUTTING THEM TOGETHER:
The tie that binds most primary and secondary backings together in broadloom products is synthetic SBR latex. For specialty applications hotmelt adhesives, polyurethane and some other products are used.
AVAILABLE SECONDARY BACKINGS:
Woven synthetic backings can range from 5 pic to 13 pic on commercial carpet. The pick is the number of weft (widthwise) or warp (lengthwise) yarns per inch. The higher the pick the more the backing material costs and the greater the dimensional stability of the backing. One of the ways the industry has cut costs in product is to use backings with lower picks. When you couple this with high filler loads in the latex there can be any number of compromises to the carpet. Some of the compromises are delamination, edge ravel, sprouting, buckling and wrinkling and overall dimensional instability issues particularly if the product is a nylon step over stitch construction. The woven synthetic backing is the most common type of backing used on carpet whether it be commercial or residential.
Unitary backings are used on commercial carpet that is to be glued directly to the substrate. This is basically two coats of latex, each with different properties. The first coat locks the tufts into the carpet and the second coat offers dimensional stability. If the carpet is a step over stitch construction it would benefit the product to add a 5 pic woven secondary backing. The reason for this is to put 100% of the carpet in contact with the floor. Without this type of secondary application only the highest tuft rows contact the floor and only those rows come in contact with the adhesive. It is impossible to achieve 100% transfer of the backing into the adhesive and onto the floor if 100% of the backing doesn’t touch the floor. The addition of an inexpensive secondary backing allows for the glue to anchor 100% of the carpet and therefore maximize the adhesion and prevent the carpet from coming off the floor. There are other factors which can cause problems but at least it won’t be because all of the carpet backing is not in contact with the flooring surface.
Attached cushion backings mostly of polyurethane can be up close to the backing or up to 1/4 inch thick. This backing system, more than any other in my opinion, does more to improve carpet performance, appearance retention and longevity, than any other backing technology. It offers cushioning comfort, insulation, noise reduction, wear resistance and extremely high structural integrity. It has been proven time and again that the face weight can be lowered by implementing a high density polyurethane cushion backing system. Years ago we tested carpet at 8 ounce face weight with this backing versus 28 ounce face weight uncushioned carpet and the 8 ounce product outperformed the 28 ounce product every time. Since almost 70% of the cost of the carpet is in face yarn, integrating an attached cushion back actually makes the carpet less expensive to make while greatly improving performance – the result is a product with much better value. You actually get more performance for less because the backing is not going to cost as much as the face yarn. Some manufacturers have found this out and are employing this concept without any compromise in product performance and without lowering the cost of the product. The end user should be paying for performance, not how much the carpet weighs. Face weights on carpet products, particularly carpet tiles, can hover around 17 ounces per yard without affecting performance or appearance retention at all. An added benefit is the carpet lasts longer and doesn’t have to go into the land fill sooner. Where carpet tiles are concerned, they can be revitalized to live again another day, greatly extending their beneficial life.
Vinyl backings are used primarily on modular carpet systems, carpet tiles and 6 foot roll goods – variations of this backing also exist. Vinyl has been the mainstay of the modular segment of the industry for years. With the concern for the environment it is particularly adaptive to accommodating recycled content which is added to it. One concern here is the addition of nylon face fiber to the backing. If the nylon is not adequately encapsulated and sealed into the backing it can promote moisture migration from conduction by the nylon in the backing which could potentially cause an installation failure or plasticizer hydrolysis. The concern for plasticizer hydrolysis when using vinyl backed goods, especially on substrates that have questionable moisture vapor emission issues, has elevated the industry’s awareness to the use of alternative backing systems. If moisture concerns are an issue, and they certainly are and should be at the forefront of everyone’s list now, then one of the best backing systems to use is polyurethane with a releasable scrim. The polyurethane will not be affected by moisture – no odor or emissions – and the scrim provides space that will allow moisture vapor to volatize.
The backings mentioned are those currently and most common used in commercial carpet. There are some others such as EVA, hot melt and Bitumen and of these the Hot Melt would be found most on domestically produced carpet products, particularly Lee’s Unibond – they’ve mastered this backing system.
What’s most important about carpet backings is knowing where the carpet product is going to be used, the conditions of the substrate and the performance expectations of the product. The backing is like the suspension system on a truck, it can be adapted to the type of use and service the product is expected to deliver. Companies such as C&A and Interface are very specialized in their backing systems and technologically advanced in the industry, in my opinion. Shaw and Mohawk also have their own proprietary specialty backings. Milliken is standardizing on their ComfortPlus polyurethane cushioned backing. Other manufacturers can adopt almost any backing they want from commercial backing suppliers in the industry whether that be print based latex to the highest quality polyurethanes. More technology exists in backings and is being developed by the industry than any other component used in the production of carpet. The backing is the foundation of the product and its importance will only grow as those specifying, selling and using it realize how important it actually is.
Author – Lewis G. Migliore – The Commercial Flooring Report
LGM and Associates – The Floorcovering Experts