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3.2.8 Creep-Rupture Performance of Adhesively-Bonded Roofing Seams

Mark G. Vangel

James J. Filliben

Statistical Engineering Division, ITL

Walter J. Rossiter

Building Materials Division, BFRL

Adhesively-bonded EPDM (a rubber material) is widely used for low-slope industrial roofing. There are two main types of adhesive systems for seams on these roofs: a liquid adhesive, and several varieties of tape adhesive. Liquid adhesive is widely used, but it is volatile and relatively expensive to apply. An objective demonstration that tape adhesives are at least as reliable as the liquid will greatly increase the use of these adhesives. A consortium of NIST, professional roofing trade associations, and roofing adhesive manufacturers was formed, in part, to perform such a study.

The chosen measure of performance for the experimental seams is creep lifetime; i.e. the time-to-failure under a constant load. In Phase I of this investigation, specimens from two tape systems and a liquid adhesive were tested in creep-rupture at various loads. The main conclusion of this phase was that the tape-bonded seams appear to perform at least as well (in terms of creep life) as adhesive-bonded seams.

Phase II of this investigation concerns the performance of tape-bonded seams under laboratory simulations of field preparation conditions. A 25-1 fractional factorial experiment involving application factors was designed and analyzed, for each of 22combinations of material factors. The application factors are

Factor Level 1 Level 2
Primer Not Primed Primed
Surface Condition Clean Contaminated
Application Pressure Low High
Application Temperature Low High
Time-at-Temperature Short Long
The material factors are two tape systems, each obtained at a thickness that is typical of what is used in practice, as well as a lesser thickness.

The figure displays the means of eight replicates for ordered factor combinations, with the material factors indicated by plot symbols. The average lifetime for liquid adhesive specimens is taken from Phase I of this study. It appears that if tape systems are well prepared (primed, cleaned, etc), then tape-bonded seams can be expected to have creep-life at least comparable to that of well-prepared adhesively-bonded seams.


Figure 18: Creep-rupture lifetime of tape-bonded EPDM seams for various combinations of application conditions.

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Date created: 7/20/2001
Last updated: 7/20/2001
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