To Power Stretch Or Not To Power Stretch
That’s a question? You’re darn right it is, and I get it all the time. “What size room do you have to power stretch?” “Why do we have to power stretch – my jobs are tight and look good; I don’t get call backs?” Or my favorite statement about kicking, “I’ve been kicking carpet for fill-in-the-blank years, and my knees are fine!” Well, let’s deal with those last two bull…er, I mean male bovine excrement…statements right off.
First of all, about kicking: It is not your knees that take the main abuse from using a knee kicker. It is your hips and the small of your back. Think about it – you rocket your knee forward powered by the muscles in your hip and the small of your back, and smash the bottom of your femur into a stationary object. The rebound of that force is absorbed by your hip socket and the small of your back. So, Mr. I-Have-Been-Doing-It-For-20-Years-And-My-Knees-Are-Fine, ever wonder why your lower back hurts so bad every morning?
What size room needs to be power stretched? My rule of thumb is, “If it is bigger than a phone booth, power stretch it! If you can get your power stretcher into a phone booth, power stretch it!”
As to why we need to power stretch, besides the obvious that it saves wear and tear on your body, it makes a better installation. Simple as that. If you have been kicking in all your jobs and say you don’t get call backs, either your customers don’t complain or you’re fibbin’.
The majority of the carpets we are stretching-in over pad have woven polypropylene primary and secondary backing, commonly known as “Action Bac,” the trademarked backing from what used to be Amaco fibers. They were the first to come out with it, so Action Bac has become the catch-all name like Coke is sometimes for soda or Kleenex for tissues.
Anyway I digress. Unlike rubber or vinyls which have memory, meaning when they are stretched they want to return to their original shape. Polypropylene has “creep,” meaning you stretch it and it wants to “grow” to that shape. Wall-to-wall installed carpet is tight to the room walls. When the carpet expansion hits the wall, it has nowhere to go. Now the carpet is too big for the room so it buckles, providing a place for the excess carpet to go. The stretch on a room of carpet is meant to be a vehicle to absorb that expansion and contraction, which happens with heat and humidity changes.
You cannot get the proper stretch on woven polypropylene backing with a knee kicker. I don’t care how big you are. Kicking is also hard on the carpet. Think about it. Power stretching is a consistent pressure applied over a 12” wide gripping surface. Kicking is a hard, sudden blow delivered by a 4” gripping surface. Which would you prefer: A slow push across the room, or getting cold-cocked and knocked across the room?
There is some confusion on proper stretching patterns for installing wall-to-wall carpet. In my opinion there is no one right way to do it. The stretching requirements will be dictated by the individual carpet and job layout. One constant that holds true is that the majority of the stretch in all carpet is in the length (with the exception of a couple of odd knitted pieces and some Wiltons).
Keeping this in mind: When stretching a piece of carpet the majority of the stretch should be angle stretches (approximately 15 degrees) along the length of the material, followed by straight or slight angle stretches across the width. Now this puts me at odds with the stretching diagrams in the back of the CRI manuals, but I disagree with those stretching patterns anyway so that’s OK.
While carpet stretches mostly in the length, some carpets (Karaloc and Axminister for example) stretch only in the length and not at all in the width. It is recommended by CRI 104 & 105 to stretch synthetic backed carpets (Action Bac) 1 to 1 1/2 percent in both the length and width. Well, that might seem a little extreme for a 12’ width when you consider 1% is 1.44 inches and 1 1/2 % is 2.16 inches, but don’t spare the horses. Stretch the carpet tight!
The following drawings are the stretching techniques that work for me.
Figure 1. This is the basic stretch for a square or rectangular room. The classic method is to reverse steps 1 & 2 so that your first stretch is at an angle to the corner. I have change this because that stretch will cause the carpet to pull away from wall B toward wall D, requiring you to whale away on a knee kicker to get it straightened out. Way too much like work for me. This way allows the stretcher to do all the hard work.
Secure 3 to 4’ of wall A, place stretcher tail on wall A approximately 2’ from the corner of A&B, stretch straight from that point to wall C. Make sure the carpet has not pulled away from wall B; if it has bump the stretcher head slightly with a kicker to straighten it out.