A Letter from Hexion on
PVAc- and PUR-based Adhesives
Over the past few months, we’ve sent you a series
of letters regarding the heat performance of various adhesives
used in finger-jointed lumber for fire rated assemblies. This
heightened correspondence has reflected a new level of scrutiny
by industry associations and building code agencies for fire-resistance-rated,
finger-jointed wall assemblies.
Here’s where we stand today.
- Questions about the performance of finger-jointed lumber
used in fire-rated walls were raised in a 2006 research program
conducted by the American Lumber Standard Committee (ALSC). Specifically,
studs made with Polyvinyl Acetate (PVAc) and Polyurethane
(PUR) adhesives did not pass the ASTM E119 one-hour burn
test, at that time.
- In response, the ALSC developed fire-resistance qualification
criteria for finger-jointed lumber adhesives. Only adhesives
which passed test Method A or wall systems which passed test
Method B (both of which prescribe an E-119 procedure) would
receive certification for use in commercial construction
and multi-family dwellings, which require fire ratings.
- A heat-resistant adhesive (HRA) labeling system was also
put in place for easy identification of fire-rated assemblies
by building officials.
- Adhesive suppliers, in partnership with finger-jointed
stud manufacturers, began conducting tests of their products
prior to and as soon as the new standards were announced
in the hopes of attaining HRA certification on behalf of
Hexion has been diligent in testing adhesives, working within
the new protocols and providing data to the grading agencies.
Based on our experience, we have come to the following conclusions.
- The key to safe structural finger-jointed lumber products
is an adhesive system with a polymer mix that remains virtually
intact as temperatures continue to rise. Thermoset resins
are the most stable polymers known to exist and should, therefore,
in our opinion, be the industry standard.
- Hexion thermosetting adhesive systems – including
our melamine adhesives MR84A/M-605LY and MR84A/M-610LY – have
passed test Method A and are being certified for unrestricted
use in fire-rated finger-jointed stud applications.
- PVA- and PUR-based adhesives simply cannot match the heat stability of melamine and resorcinol based adhesive systems. Third party testing has shown PVAs and moisture cure PURs fail ALSC's Elevated-Temperature Adhesive Qualification Procedure. We are skeptical
that any PVA or PUR adhesive will ever qualify for HRA certification
under test Method A, which most fully stresses the test wall
- Finger-jointed lumber has seen steady market share growth
over the past ten years because it has promised benefits
over solid sawn (such as straightness and ease-of-use) with
interchangeability in fire performance. Specifying adhesives
that deliver anything less than absolute interchangeability
undermines the industry’s value proposition and opens
manufacturers up to public relations issues.
- Because of our concerns, Hexion is not currently planning
to continue research on PVAc- or PUR-based adhesives for
structural engineered lumber applications, including finger-jointed
studs for fire rated assemblies.
At Hexion, we believe the best way to move forward is to embrace
rigorous testing protocols and hold ourselves up to the highest
heat and fire performance standards.
If you have any questions about our position on PVAs and PURs,
or would like more information on our products that have met
the highest Heat Resistant Adhesive (HRA) standard, please
contact Dan Allen (+1 336 884 8918), Greg Clark (+1 630 400
9820) or Scott McIntyre (+1 541 517 3433).