Carpet backing delamination:
Excess heat can affect the latex binders used in the making of most common carpet backings. Too much heat can cause them to degrade rapidly and break down. The result would be a seam that was bonded on the base but would still peak since the bond between the primary and secondary backings had broken.
Many urethane rebond and other carpet pad types are also sensitive to excessive heat. Leaving a hot iron in one place for an extended period of time will cause the pad to compress and lose resiliency. This will result in a channel (lower profile) running the length of the seamed area (Illustration B and Photos 5-7). How do you avoid this? Seaming on a hard surface ensures tight seams and proper hot melt adhesive transfer, and low melt point seam tape should be used.
Carpet texture is created using a heat process. Adding heat back into the material (face yarn) and then crushing it or deforming it with the wrong type of seam roller or the wrong type of seam weight can re-crimp the face pile, leaving a telegraph of where the seam was placed (Illustration C). How do you prevent this? Never use a star roller on a hot seam; always seam in the direction of the pile; and use a heat-dissipating seam weight.
Seam tape bonding to the pad: Allowing the iron to get too hot over most any tape or not moving a hot iron fast enough can cause the hot melt adhesive to bleed through the paper, causing it to adhere to the top of the padding. This becomes a problem during the stretch-in process, and can cause a bunching up effect of the pad under the carpet (Illustration D). How do you avoid this? Use a low melting point seam tape.