ICS Magazine

What Every Cleaner Should Know About Direct-Glue Installation

April 8, 2009


Cleaning commercial carpet installed with the direct-glue method is probably one of the easiest challenges a professional technician will face.

This is especially true when the carpet has attached cushion, or when it is installed with the double-glue method.

If the carpet is installed directly onto a subfloor and there is no cushion present to absorb the impact of traffic, and especially if daily vacuum maintenance is lacking, the carpet eventually shows the effect of exposure to abrasive soil – a condition called shading. Traffic lanes become dull and dingy due to the action of abrasive soil rubbing against the sides of plastic-like fibers, which causes a physical change in their appearance. Not much a cleaner can do about that.

Direct-glue adhesive holding the carpet to the subfloor can fail for a variety of reasons. Sometimes that failure isn’t noticed until cleaning is completed. At that point, carpet components can absorb moisture and swell, showing unsightly ripples in traffic lanes.

The cleaner isn’t the cause. He’s simply the last to touch the carpet, and therefore, he gets the blame!

Since forewarned is forearmed, cleaners should raise the question, “What causes a direct-glue installation to fail?” Usually, there isn’t one simple answer.

Recently, I inspected a new installation of nylon-faced, polypropylene-backed unitary-constructed carpet direct-glued to concrete slab in which a number of seams separated due to carpet shrinkage.

“What?” you say, “How could an all-synthetic carpet shrink?”

The answer is, normally it doesn’t – if installation specifications are followed meticulously.

While there isn’t much that a cleaner can do about direct-glue installation failure by the time cleaning is called for, he or she should at least be aware of potential problems that might contribute to that failure. Both the Carpet and Rug Institute standards for residential and commercial installation, as well as carpet manufacturer instructions, provide guidance for direct-glue installations.

Specifications for preparing and direct-glue installing carpet (double-backed or unitary) to concrete slab can include, but are not limited to:
  1. Ambient temperature should be between 65-95°F/18-35°C, with a maximum RH 65%. These conditions should be maintained for at least 48 hours before and during installation, and for 72 hours after completing installation.
  2. Installers should ensure that the building HVAC system is operational, and that ambient installation conditions are met.
  3. Building owners, or, in the case of new construction, the general contractor should ensure that the concrete slab vapor emission rate is three pounds per 1000 ft2 over 24 hours (ASTM 1869-98 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride), or <80% RH (ASTM F2170-02, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In-situ Probes).
  4. Installers should ensure that slab temperature is at least 65°F/18.3°C to avoid dew point or condensation temperatures that decrease vapor pressure on slabs relative to atmospheric conditions above it, and prolong adhesive curing.
  5. The carpet should be delivered to the job site at least 24 hours before installation. The carpet should be unrolled to relax and acclimate it to site conditions.
  6. Installers should ensure that that the subfloor is clean and dry and that:
    • hydrostatic pressure is relieved
    • free of standing or excess moisture
    • free of contaminants (particles, dust, oil, grease, solvents, wax, floor finish, alkali residue, paint, cut-back adhesive, or other substances) that might impede adhesion.
  7. Installers should ensure that the subfloor pH is between 7 and 9; if over 9, corrective measures are required.
  8. Installers should ensure that the subfloor is structurally sound.
  9. Installers should prepare the subfloor by:
    • patching and leveling joints, cracks and uneven areas with appropriate compounds,
    • curing patching and leveling compounds at least 24 hours before applying adhesive.
  10. Installers should select and use a carpet-manufacturer-approved adhesive.
  11. Installers should apply adhesive with an appropriate trowel that ensures adequate coverage by:
    • selecting the proper notch configuration (“V” or “U” notch),
    • ensuring proper notch width and depth,
    • trowels should be repaired or replaced before beginning the installation, and re-notched periodically on large jobs when wear is encountered.
  12. Installers should ensure 100% adhesive coverage of the subfloor surface.
  13. Installers should consider the texture of the carpet (e.g., unitary, attached cushion, woven or spun polypropylene) being installed, and ensure adequate adhesive transfer to the carpet backing, including recessed areas. With cushion backed goods, 100% transfer of adhesive from the subfloor to the backing is possible; with unitary carpet or other textured backings, this can be a challenge.
  14. Installers should allow 20 minutes for adequate curing (longer if atmospheric conditions are damp or a concrete slab is <65°f/18.3°c). Installers should check adhesive curing by laying out carpet and then, lifting the carpet and observing to see if the adhesive develops strands or “legs” between the subfloor and carpet backing when lifted.
  15. Installers should compression roll the carpet to ensure adhesive contact and penetration. With smooth, cushion-backed carpet, rolling can be achieved with a carpet core. However, with highly textured backings, a compression roller (<75 pounds) is required to achieve adequate adhesive transfer. Over-rolling the carpet, especially before the adhesive is allowed to “tack up,” can lead to adhesive failure. In some cases, it may be prudent to re-roll the carpet within 3-12 hours of installation.
  16. Installers should advise building owners or managers to restrict foot traffic, and especially rolling traffic, for 24 hours after installation.


While skipping or minimizing one single specification above might not cause problems, two or more in combination can result in adhesive failure or seam separation over time. Carefully adhering to industry installation specifications is particularly important when unitary carpet constructions are involved, which inherently have less dimensional stability. Without a secondary backing, more latex should be used to achieve unitary dimensional stability. When that latex absorbs moisture – especially if not adequately acclimated to site conditions – it swells upward and draws the carpet in from the outer perimeter and at seams.

OK. Probably a lot more than any cleaner ever wanted to know about direct-glue failure, right? But the information may come in handy at sometime in the future when all fingers point to you as the cause of direct-glue failure.