Carpet

Peaked and Visible Seams

Why stretched seams peak, what CRI says about seam visibility, and how iron temperature, tape, edge sealing, rollers and weights affect the result.

Updated · 3 min read

Some seam visibility is normal. Seams are a necessary part of carpet, and no one can guarantee they'll be invisible.[1] What you can control is peaking, gaps and fuzzing, and most of that comes down to seam placement, iron temperature and how the seam is built.

Symptoms

Match what you see to the likely cause.

What you see Usually
A raised ridge along the seam, one side lighter than the other Peaking
Backing showing, or a gap between edges Poor trimming or edges not butted
Fuzzing or yarn pulling out along the seam Edges not sealed
Shrunk or discolored backing Iron too hot

Why seams peak

Some peaking is expected whenever carpet is stretched. As the carpet is stretched, the tape is pulled upward toward the center of the backing, lifting the seam and opening the pile in a V. Light falling across it makes one side look lighter.[1]

Likely causes

These turn normal peaking into a callback.[1]

  • Iron too hot: excess heat distorts and shrinks synthetic backings, and the shrinkage makes peaking worse.
  • Narrow tape: wider 6" tape spreads the stretch over more area.
  • No pre-stretch: pre-stretch parallel to the seam, 1% to 1-1/2%, for about 18" on both sides.
  • Soft work surface: seams should be made over a firm, flat surface. Thick, soft cushion makes a good seam hard to build.
  • Seam placement: where you can, run seams toward the main light source.

Building a seam that lies flat

The installation standard sets these seaming rules.[2]

  1. Plan seams to run the length of the room, parallel to traffic, and not across light or doorways.
  2. Trim edges cleanly. See Cutting carpet seams.
  3. Seal both edges unless the carpet maker says otherwise, and let the sealer dry.[2]
  4. Work over a seam board. Use tape with at least 2-3/4" of adhesive width.[2]
  5. Set the iron for the tape. For Roberts Heat Bond tapes, start at 2 to 3 on the dial and test the iron on scrap tape first.[4] A Crain No. 905 at full heat seams at 3 to 4 ft per minute.[5]
  6. Run the iron in the direction of the pile with a heat shield.[2]
  7. Roll the seam, but not with a star or spike roller, especially on cut or cut-loop carpet.[1]
  8. Weight the seam with wood or another non-conducting weight. Metal traps heat and moisture.[1]

How to fix it

What to do depends on the cause.

  • For peaking from inadequate stretch, restretch with a power stretcher. Stretch 1% to 1-1/2% in each direction; a knee kicker can't get there.[3]
  • For a seam with gaps, unsealed edges, or backing damaged by heat, the seam has to be cut out and remade with new tape.
  • Check the pad under the seam. Make sure the cushion hasn't wrinkled.[3]

When to replace instead of repair

Scorched or shrunken backing can't be recovered. Cut back to undamaged carpet, seam in a new piece, and test the iron on scrap first.

Tools we carry

These are the irons, weights and rollers we stock.

Iron problems are covered in Seaming iron troubleshooting, and technique in Hot-melt seaming.

References

  1. CRI: Peaked seams in stretch-in carpet installation
  2. CRI 105: Residential carpet installation standard
  3. CRI: Guidance for restretching
  4. Roberts: Heat bond iron owner's manual
  5. Crain No. 905 manual
  6. Roberts 10-286G 6" seaming iron (product page)
  7. Taylor 893 seaming iron (product page)
  8. Gundlach seam weight (product page)
  9. Roberts 10-124 cut pile seam roller (product page)

Linked PDF documents are archived copies saved by PreFloor Tools so they stay available if the publisher moves or removes them. Check the publisher's website for the latest revision.

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