The following problem has been an issue for several years. I wrote articles about this at least 15 years ago and the industry has known about this since long before then. The problem of which I speak is the installation of step over stitched, shifted or graphics constructed, latex unitary backed carpet and it’s propensity to shrink, in the width, in as little as 24 hours after having been installed. This can also happen with woven polypropylene backed carpet as well. Knowing this can happen and that there is a technique and manufacturing process that can prevent it will keep you out of trouble. You can count on someone contacting our office with this problem regularly.
If the flooring contractors contacting us are having this problem it’s a sure bet a lot more contractors have the same problem. Those who don’t know about this problem are getting blamed for something that’s preventable and controllable but very difficult to fix and resolve after it manifests itself.
I want to give you a very specific example of a recent problem experienced by a flooring contractor and some of the ambiguous and downright incorrect information and responses he got from people who are supposed to be knowledgeable including, in this case, the manufacturer.
This particular installation was in a city government building. The carpet was a latex unitary backed product with a step over stitch construction – this means the yarn on the back was interlaced, similar to a chain link fence. On the surface the carpet was not patterned but a multicolored tweed level loop. Looking at the face of the carpet would give you no indication the product was tufted on step over stitch machine. The contractor, therefore, had no indication he might have an issue with this product even if he was aware that latex unitary backed carpets like this could be dimensionally unstable. (I’ll explain why later)
As it was explained to me, they used a premium multi-purpose adhesive with a 1/8×1/8×1/8 inch “U” notched trowel with a spread rate of about 7.5 yards per gallon over a Luan substrate. The carpet was laid out, the selvedge trimmed and it was fully acclimated for over 24 hours prior to installation. The carpet rolls had also been stored in the building for three months prior to installation. The carpet looked perfect when the job was completed, then came the problem.
The carpet contracted, pulling away at the seams and from the perimeter walls. No one could understand why. There were two independent inspections performed on this carpet, one commissioned by the manufacturer and one by the flooring contractor. One report describes the seams as being tight in some areas, intermittently gapped in others and gapped by as much as one inch in one seam. The seams were sealed because loops were being pulled out of one side of one panel and the seam sealer was holding them. Where carpet had lifted forming humps it was pushed back down into the existing adhesive and it strongly resisted being pulled back up. This indicates the tenacity of the adhesive was still good. In other areas the inspector said there was no transfer of adhesive to the back of the carpet indicating too much open time for the adhesive. The carpet was rolled immediately after installation with a 75 pound roller, as specified by the manufacturer and then again later. The inspector said a humidity test revealed low humidity and this might be the reason the adhesive had dried quickly. The temperature is fluctuated in the building during use and non-use times and this will have an affect on the carpet causing a gain and loss of moisture and an expansion and contraction of the product. Also suggested was a dimensional stability issue with the carpet and that it might be a possible contributor to the problem. No definitive conclusion was reached by either inspector so no one would know what happened here and why. The manufacturer interpreted their report to mean that this failure was completely the result of installation – it wasn’t.
The second report stated that the carpet was not acclimated, not rolled, too much open time of the adhesive and that there may also be a dimensional stability problem with the product. All of this was suspected, none of it was definitively determined nor was there any conclusion in this report. This inspector feels corrective action can be taken by installing saddles where the seams have opened. This was tried and not accepted by the end user. In fact, after the saddles were placed in the seams the carpet panels on either side moved more and buckled again.
This is only one case, there’s more. Another flooring contractor sent us information on a problem they have with shrinking carpet. This product was also a graphics construction but it did have a woven secondary backing. It shrank after a couple of months on the floor. The installation looked perfect when the job was finished and then, all of a sudden, the material started to separate at the seams. The contractor went back, on several occasions, and attempted repairs of varying kinds. The material was installed on both concrete, primarily, and on some plywood. This made no difference because the carpet shrunk on both surfaces. A high quality adhesive was used, the seams were sealed and still the carpet pulled apart at the seams. The same product in another part of the facility, has never exhibited a problem. Again, two inspectors looked at the carpet. One felt it was a problem with the product and the other felt it was installation but neither came to a conclusion. The reports from all of these people are open to interpretation and can be massaged to gain an end. How can you determine what’s wrong, who’s at fault, why and what can be done to correct or resolve the issues if there is no conclusion from the so called experts? This is a very frustrating situation and indeed indicates that the guys being trusted to tell you what’s wrong and why don’t know the product, haven’t researched the problem and can possibly come up with a cause or place blame where it should be placed. In these cases, you get what you pay for, which is very little.
Next, and possibly the most scary part of the shrinking carpets, is that the manufacturers don’t know what’s wrong with them or why they’re shrinking. Case in point is the same product from one manufacturer, on a different floor, in a different color, is not shrinking and has never presented a problem, why? They’re not sure. How could the same product be dimensionally unstable one day it’s manufactured and not on another day? There are variables that could make this happen, so let’s analyze the construction of the product to determine what these are.
This information is repetitious because I’ve written about it before but it’s important it be addressed again for the sake of hopefully helping to prevent this problem. First of all remember this statement, which I learned many years ago in this industry. “Either you control the carpet or the carpet controls you.” I was taught this by a man who I consider one of the unheralded eccentric geniuses of the industry. They were working with new technology and had to learn as they went. They found what worked and what didn’t putting backings and backing finishes on carpet. The learned what was stable, what wasn’t, why and how to make it stable if it wasn’t.
Thus the statement that you must control the carpet during manufacture to insure it’s stability or suffer the consequences of not doing so. You have also got to heed the physical characteristics of the product and know how it will respond in the installation environment in every way. It’s not enough to determine if the product is stable when you make it, but it also has to be determined if it will remain stable when installed, using different adhesives, on different substrates with varying atmospheric (heat and humidity) influences.
How big an issue is this really? If the last month is any indication, this is a major concern in the commercial environment. I have had calls and letters from commercial flooring dealers with shrinking carpet problems lately that we are addressing as well as conversations and meetings with commercial carpet manufacturers recently. What’s happening is this. The carpet is laid out, the selvedge trimmed and the product acclimated on site, in most of these cases. The substrate, again, in most of the cases, has been checked and tested for moisture vapor emission. A high quality adhesive is applied, or so it has been said, in most cases, and the carpet installed with the seams being sealed. After as little as 24 hours the seams, which were tight when the installation was completed, separate and the panels on either side shrink as much as ½ inch total.
This occurs either uniformly or sporadically. In almost all of these cases the carpet is a graphics tufted (step over stitched) nylon. The significance of the nylon yarn is that it will gain and lose moisture, up to 4 ½% and in doing so it will expand and contract. The significance of the step over stitch construction is that the yarn is stepped over, making it intertwined on the backing. The gain and loss of moisture in the nylon yarn will cause the carpet to contract or shrink in the width because the step over is in the width. Simply put, all the tension in the carpet will be in the width, not in the length. The volatizing (drying and evaporating) moisture from the adhesive can act as a catalyst in the gain and loss of moisture and cause the carpet to shrink. Is this reaction any different with a straight row stitched product? Yes. The straight row stitch construction has no cross over in the yarn. Each row is separate and does not intermingle with any other yarn, therefore there is no inherent tension built into the carpet. Even though the nylon will still gain and lose moisture, which may effect some movement in the carpet, there is no widthwise reaction that will affect the seams.
The shrinkage can and does occur in periods of time greater than 24 hours. In some cases it has been months since any shrinking was noticed. Why is this? There can be several reasons. First, there may be an ambient change in the environment caused by changes in the settings of the air handling systems. There can be changes in the natural air from increases or decreases in heat and humidity. There could be a compromise of the adhesive from tackifier destruction caused by moisture vapor emission in the substrate that carries with it alkalinity which will destroy adhesive tackifier. The adhesion of the carpet may have been weak to start with and, over a period of time, enough compromise may have occurred in the adhesion, either from traffic, cleaning or stresses of moisture gain and loss, to break the bond of the adhesive allowing the carpet the freedom to move. Using seam sealer is no guarantee the seams will not open up. The force exerted across the plain of the carpet from the stress created in the gain and loss of moisture can pull the seams apart. In fact, the sealer may hold and the carpet itself could pull apart at the edge. What is this inherent tension built into the carpet in a graphics tufted product? You have to understand the manufacturing process to understand the physics in place here. First, the carpet is tufted into a woven polypropylene primary backing which is held very taught during the tufting process. When the two shifting needle bars insert the yarn they exert a lateral force on the backing. When the tufted material is finally released from the tension on the tufting machine the backing material will naturally want to return to where it was but the yarn is pulling in another direction. When this material goes to the finishing range for backing it is again pulled out in the width. Either a latex unitary or low pic woven polypropylene backing is applied at this point and then the product goes into the drying range for curing. The length of the drying range, temperature and time in the range could effect additional tension or dimensional changes in the polypropylene backing as well as drying out the yarn, this instigates some dimensional change in the product. Now, at the job site the carpet has a built in memory and it will try to get back to where it wants to be as well as being influenced by environmental reactive changes affecting the material. The nylon will react to gain and loss of moisture and the polypropylene will react to gain and loss of heat. There’s a fight going on in the product for positioning. This is the law of science and physics at work.
Can this shrinkage be prevented and how? There are several ways it can be. The first is to tuft into a non-directional primary backing. These types of backings tend to keep the carpet much more dimensionally stable. Second is to put a more dimensionally stable secondary backing on the product. Shaw and SI, for example, have developed a few new backings which hold the product stable and enhance installation. Application of a polyurethane backing will keep the carpet much more dimensionally stable as well. The carpet must be acclimated on site, the temperature and humidity must be controlled and the substrate tested for moisture. A premium adhesive must be used and transfer of adhesive between the substrate and the carpet backing complete. Using the contact method of installation will help immensely in tenaciously holding the carpet in place. The seams must be sealed and, if deemed necessary and reasonable, a very low profile seam tape used as insurance.
Shrinking, or movement in the carpet, is an inherent condition built into the product. Excessive movement indicates the product is not under control. Shrinking may be blamed on installation but the movement is actually a physical reaction of the carpet to an on site stimulus or the product trying to get back to the position it remembers. Despite the best installation practices, shrinkage may still occur. In fact, if the adhesive is heavy and has a lot of body, developing lots of legs, the reacting carpet may move right across the top of it. Once energy is allowed to build up in the carpet there is a tremendous amount of force generated across the carpet and one way or another it will find a way to move and distort itself. This movement is exhibited most graphically in the seams shrinking when in fact the entire carpet has shrunk.
As long as the conditions exist, either inherently in the construction of the or on the job site, you have to be keenly aware that the potential exists for graphics tufted carpets to shrink when glued directly to the substrate. This is nothing new. Have your concerns before the job instead of headaches afterwards. Call me if you have any questions or when you need help. Remember, the carpet never lies, it will always tell you what’s wrong if you know how to interpret what it’s saying. And, there is always a conclusive answer for every problem, accept nothing less.
Author – Lewis G. Migliore – The Commercial Flooring Report
LGM and Associates – The Floorcovering Experts