A Letter from Hexion on
PVAc- and PUR-based Adhesives

Dear Customer,

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 the Industry.

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.

1. 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.
2. 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.
3. 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 system.
4. 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.
5. 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).