Construction Concerns: Adhesives and Glues

Article and photos by Gregory Havel

We are all familiar with adhesives and glues: the materials used to make things stick to each other:

Simple water-soluble pastes used to attach wallpaper to walls and clippings to scrapbook pages
The sticky backing on duct tape.
Water-based polymer glues used for furniture repair and woodworking.
Solvent-based glues used for plastic models and appliance repairs.
Complex resins and polymers used to assemble manufactured wood products.
Epoxy adhesives used to join steel, concrete, and other materials.

For the best results, the right glue must be used with each material and must be selected based on the amount of weight it will be expected to support.

For an adhesive to work properly, the surfaces to be joined must be clean and prepared for joining. Both surfaces must be compatible with the adhesive to be used. The adhesive must be allowed to cure under the proper conditions for at least the minimum amount of time to achieve full strength.

Some adhesives work best with two smooth surfaces; others require the surfaces to be roughened or coated with a primer. If the surfaces aren’t properly prepared or aren’t clean enough, the joint will not be strong and will fail under stress. If the adhesive cures at a temperature that is too hot or too cold or if the joint is stressed before it has cured long enough, the joint will also fail.

Firefighters must be aware that many of today’s construction components are manufactured using adhesives or are assembled with adhesives during construction.

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Manufactured wood products are made of thin veneers, shavings, chips, slivers, or fibers of wood joined by adhesives (usually phenolic resin or urea-formaldehyde glue) that are cured in a heated press and then cut into the sizes and shapes needed. Photo 1 shows the end of a manufactured wood beam made of parallel-strand lumber (PSL), using wood slivers and phenolic resin glue. Photo 2 shows the face of a sheet of oriented strand board (OSB) using wood shavings mixed with adhesive. Some wood trusses are also assembled with adhesives instead of mechanical fasteners.
Plastic products are often assembled at the construction site using adhesives and glues. They include PVC drain, waste, and vent (DWV) pipe; piping for water, natural gas, compressed air, and other fluids; rain gutters and downspouts; sheets of flooring material; plastic decorative beams and trim; and others.
Manufactured wood products are often glued to each other and to dissimilar materials at the construction site for added strength or stability. Subflooring (OSB or plywood) is often glued to the joists that support it either for more strength than is provided by nails alone or to prevent the floor from squeaking in the future. Gypsum drywall board is often glued to wall studs and ceiling joists in addition to, or in place of, the traditional nails or screws.

Failure of adhesives under fire conditions can lead to partial or total structural collapse.

The adhesives used in manufactured lumber are known to begin to weaken at or near the temperature at which they were cured, which is hundreds of degrees below the temperature at which the wood ignites. When ignited, the adhesive will burn like wood and may have a higher rate of heat release and flame spread than the wood it joins.
The adhesives used to join lumber and other products will burn. If used in the proper quantity for the application, they may or may not accelerate the flame spread. If there is a lot of excess adhesive, it will add fuel to the fire and increase its rate of flame spread.
Failure of adhesives in wood trusses or I-joists by heating or burning can cause the f floors, ceilings, and roofs to collapse under or on top of firefighters.
Failure of adhesives attaching gypsum drywall board to wall studs or ceiling joists can drop these panels onto firefighters.
Failure of adhesives used to attach plastic cornices and decorative beams to walls and ceilings can injure or trap firefighters.
Even if the adhesive was manufactured with a flame-retardant chemical in its formula, it will still burn; however, it will ignite at a higher temperature and burn more slowly and with more smoke. If burning, it will extinguish itself when the flame impingement or other heat source is removed.

Adhesives are known to fail without fire present. We have all opened a 50-plus-year-old photo album or scrapbook and watched as the glue or paste used to attach the photos or clippings disintegrated. Anyone who has renovated an older home knows that the old wallpaper must be removed before the new paper is hung or the new paint is applied. Old wallpaper tends to become loose and to peel easily. The adhesive used to attach vinyl floor tile and sheet flooring can loosen with age.

Adhesives can be said to achieve their maximum strength at the time they finish curing and to gradually begin to lose their strength as they age. This aging is a combined function of age, seasonal and daily temperature changes, seasonal changes in humidity, exposure to ultraviolet light (sunlight), vibration, flexing (loading and unloading), wetting and drying cycles, and other stresses and factors. The more factors that are involved at a location and the more frequently they change, the more rapidly the adhesive will age and weaken.

Perhaps we can say that adhesives have a “half-life,” something like radioactive materials. After exposure to aging influences, adhesives will reach a point at which they will be only half as strong as they were at the time they finished curing, a point at which there no longer will be a safety factor. This half-life could be as short as a few minutes if the surfaces joined by the adhesive were not clean or properly prepared, if the adhesive was incompatible with either or both of the surfaces that were joined, or if the joint is severely overloaded. This half-life could be years or decades, depending on the strength of the adhesive bond and the aging influences present.

In any case, we need to be aware that today firefighters work inside structures that depend on adhesives for their stability and unity and that these adhesive bonds may not be as permanent as their manufacturers claim in advertisements.

Gregory Havel is a member of the Burlington (WI) Fire Department; a retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. Havel has a bachelor’s degree from St. Norbert College; has more than 30 years of experience in facilities management and building construction; and has presented classes at FDIC.