The Carpet That Rippled After Six Months

Why this matters

Ripples in wall-to-wall carpet are the callback every carpet crew has handled, and the reflex fix is a restretch. Usually that is right. This case is the one where the restretch was right, done properly with a power stretcher, and the ripples came back anyway the next summer, because the carpet was sitting on a cushion it could not hold its stretch over. The second fix meant telling a homeowner that the soft cushion they had asked for was the reason their carpet kept failing.

The first failure

A homeowner had the shop install cut-pile carpet in a 12 by 14 foot primary bedroom in February. She had asked for the softest cushion available, and the salesperson sold an upgrade: a 1/2-inch, low-density cushion, noticeably plush underfoot. The install crew stretched the room with a knee kicker only and trimmed in.

By August, six months on, the carpet had loose waves running across the room, worst along the path from the door to the closet and beside the bed. The homeowner said they showed up during a humid stretch in July and did not go away when the air conditioning caught up.

The first diagnosis came from a different crew on the callback: the carpet was loose, and it was loose because it had been kicked in, not power stretched. That was correct. A knee kicker is a positioning tool. It grips the carpet a few inches from the wall and gets it onto the tackless strip, but the stretch it produces comes from one knee strike over a short distance, and it cannot pull the slack out of a full room. A power stretcher braces against the opposite wall with a tube and puts a controlled, sustained pull across the whole run. The Carpet and Rug Institute's installation standard, CRI 105, in substance calls for power stretching on wall-to-wall carpet installed over separate cushion, with the kicker reserved for positioning and small areas like closets; check the current edition.

The first fix was correct too. The crew released the carpet from the strip on two walls, power stretched it length and width per the carpet maker's instructions, reattached it to the tackless, and trimmed off about an inch of excess on the length wall. The ripples were gone and the carpet sat tight. The ticket was closed in September.

It came back

The following June the homeowner called again. Same room, same pattern, ripples across the traffic path and beside the bed, a little milder than the first time. The tackless strip was still nailed down, the carpet still on its pins, nothing torn loose at the walls.

That combination is a specific signal. Carpet that relaxes again after a proper power stretch, with the edges holding, is not a stretching problem anymore. The carpet itself grew, or something is working it loose from the inside of the room. The crew lead who took this call went looking at what the carpet was lying on, after clearing three faster explanations.

• The edges let go. Tackless with pins worn flat, strip nailed too far from the wall, or carpet tucked without catching the pins all let a stretched carpet creep back. He ran a hand along every wall: the carpet was hooked on firm strip all the way around. Cleared.
• A heavy load dragged across it. Sliding a loaded dresser or a bed on casters can shove a wave into carpet that then never relaxes out. The homeowner had moved nothing, and the ripples followed the walking path rather than any piece of furniture. Cleared.
• The restretch went one way only. A crew that stretches length but skips width leaves slack in the unstretched direction. The September ticket recorded both directions stretched. Cleared.

None of those fit, so the carpet was relaxing from within the room, and the next place to look was underneath.

What the cushion was doing

He pulled the carpet back from the closet corner and lifted the cushion. It measured just over 1/2 inch with a ruler, and its label gave a density well under what the carpet maker listed.

The carpet maker's installation and warranty documents for that style specified a maximum cushion thickness of 7/16 inch and a minimum density (both figures are this product's; read yours, and see related: Carpet Cushion Types and the Maker's Cushion Spec, which owns the cushion rules). The installed cushion was over the thickness limit and under the density.

The mechanism is mechanical and it is why the restretch could not last.

• A soft, thick cushion lets the carpet flex deeply with every step. The backing bends down into the cushion and back up, thousands of times along a traffic path. Each flex works the backing's yarns and its latex bond, and a carpet worked that way slowly lengthens.
• Stretch is stored tension. A power stretch puts the carpet in tension wall to wall. Deep flexing over soft cushion bleeds that tension off over a season, faster where traffic concentrates, which is exactly where the ripples formed: the door-to-closet path and the side of the bed.
• Humidity speeds the relaxation. Carpet backings and their latex take up some moisture in humid weather, and a carpet already losing tension shows it first in summer. That is why both failures appeared in summer. Humidity was the timing, not the cause; a carpet held tight over a firm cushion rides through the same summer.

The first callback crew had fixed the symptom with the right tool. Nobody on that ticket had asked what was under the carpet, because the kicker-only install was such an obvious cause that it ended the search.

The conversation about the cushion

The crew lead's job on site was to explain why the fix the homeowner was paying attention to, the stretch, was not the fix that mattered. He showed her the ruler on the cushion and the carpet maker's page with the limit on it.

He told her the cushion she liked was the reason the carpet kept loosening: soft enough that the carpet moved with every step, and over the maker's limit. Restretching again over the same cushion would buy another season and fail the same way, and each restretch trims more carpet off the length, which runs out eventually. He also told her plainly that a cushion over the maker's limit could put the carpet's warranty at risk if she ever needed it, which is the maker's position written in its own document.

She asked whether a thinner cushion would feel hard. His answer was that a denser cushion at 7/16 inch or less still feels like carpet, and a firmer feel under the traffic path was the trade for a floor that stayed flat. She agreed to the change. The shop also owned its part: the cushion was its sale and its install, and the cushion swap went on the shop's warranty ticket.

The repair

1. Inspect the carpet before committing to reuse it. A carpet flexed over the wrong cushion for sixteen months can delaminate, its secondary backing separating from the primary. The crew lead tested at the edges by pulling the secondary backing at a corner: it held firmly, and there were no soft, bubbled areas in the traffic path. The carpet was reusable. Had it delaminated, the carpet would have been replaced, not restretched.

2. Pull the carpet and cushion. Furniture out of the room first, with two people on the dresser and bed frame. The crew released the carpet from the tackless on all four walls and rolled it back face in. Tackless pins are sharp and angled toward the wall: gloves on whenever hands work along the strip, and the strip inspected for loose sections and renailed where needed.

3. Install a cushion that meets the maker's spec. A firm cushion at 7/16 inch and the maker's density went down, seams butted and taped, stapled per the cushion maker, and trimmed to the tackless. See related: How to Install Tackless Strip and Carpet Cushion. At each wall the finished edge sits like this:

     wall
       |  stretch pulls the carpet toward the wall  <---
       |\__________________________________________ carpet
       | | \ \ \ \  |::::::::::::::::::::::::::::: cushion
       | |[tackless]|  firm, 7/16 in
 ======|=|==========|============================ subfloor
         ^          ^
         carpet     strip's inside edge: the cushion
         tucked     butts here, never up on the strip

4. Power stretch the room. The crew ran the stretcher in the pattern set out in 'How to Power Stretch Carpet into a Room', starting from a corner hooked on the strip, length then width, with the stretcher's foot braced on a wall plate or protected block against the opposite wall so the brace does not punch through drywall. The power stretcher's head can kick back if the teeth slip; the operator keeps the lever under control with both hands and nobody stands in line with the tube. The trimming knife goes away from the body with the blade changed often.

5. Trim, tuck and check. About another 3/4 inch came off the length. The carpet was tucked at the walls and the transition at the bedroom door was refit.

How it was confirmed

The finish test on day one was a walk across the room in socks along the traffic path: no waves, no soft drag, the carpet sitting flat and taut. The real test was the next summer. The shop scheduled a check in late July, after the humid stretch that had triggered both earlier failures: the carpet was flat across the traffic path and beside the bed.

What changed at the shop

Two things, both upstream of the crew. The cushion upgrade list was cut to cushions that meet the specs of the carpet lines the shop sells, and the sales sheet now prints the carpet maker's cushion limits next to the cushion choices, so a customer asking for "softer" is offered softer within the spec. And the callback checklist for ripples now has a cushion line before the restretch line: thickness and density measured and compared against the carpet maker's spec, every time, before anyone picks up a stretcher.

References

• CRI 105, Standard for Installation of Residential Carpet, Carpet and Rug Institute, current edition.
• Carpet manufacturer's installation and warranty documents, including cushion thickness and density limits.
• See related: Carpet Cushion Types and the Maker's Cushion Spec; How to Power Stretch Carpet into a Room; How to Install Tackless Strip and Carpet Cushion.
• See related: Carpet Construction for Installers.