What to do when polyurethane glue works too well.
Q. The base of my lamp separated so I applied a small ring of Gorilla Glue around the Lucite bottom and set the top of the lamp on it. I used only a small amount.
A few days later, I went to lift the lamp, and the top again separated from the base. The glue had seeped down inside of the Lucite and glued it to the top of my wooden TV stand. How do I fix this without ruining the top of the cabinet?
A. Gorilla Glue, with a name that's been a huge marketing success, is one of the best-known brands of polyurethane glue, a category that performs very differently from the white and yellow glues familiar to most consumers.
The Gorilla Glue Co. puts its brand name on a variety of adhesives, including epoxy and traditional water-based wood glue, but its Original Gorilla Glue, a polyurethane adhesive, is the most well-known.
That's the product you used, judging from the ring of foamlike adhesive residue visible in the photo you sent. And from the label on Original Gorilla Glue, it would certainly seem to be an appropriate choice. "Bonds Virtually Everything," the big print says. And in smaller print: "Bonds: Wood, Stone, Metal, Ceramic, Foam, Glass & More!"
The instructions say to scuff up shiny surfaces, such as metal or some plastics, then mist one surface with water, apply glue to the other surface, and clamp them securely for at least one to two hours while the glue cures. (With dense hardwoods, the instructions say to mist both surfaces first.)
Embedded in those simple instructions are some nonobvious technical issues that make polyurethane glue different from white or yellow glues, which are classified as polyvinyl acetates, or PVA glues. PVA glues, which include the white glue used in classrooms and waterproof formulas such as Titebond III Ultimate Wood Glue, cure by dehydration.
The moisture in the PVA glue needs to evaporate or get soaked into the surface being glued. One side effect: The glue shrinks as it dries, to compensate for the loss of water.
Polyurethane glue, however, doesn't cure by drying. It cures through a chemical reaction that requires moisture. Misting at least one surface before applying the adhesive ensures enough moisture to cause the adhesive to foam and expand, and then cure.
Polyurethane glue can be helpful in certain situations, such as when you want to glue the end grain of a piece of wood to another piece of wood. Wood fibers are like straws, and when you spread any kind of glue on the end grain of a board, the glue is sucked up into the wood. PVA glue shrinks as it cures, so when you glue the end grain, the joint winds up with almost no glue and is weak. But because polyurethane glue expands, it creates a much stronger joint. For a landscaping project, in which you are probably using fairly wet wood, the benefits multiply.
But the expansion of polyurethane glue is a benefit only if the two surfaces are securely held together with screws, clamps or even tightly wrapped tape while the adhesive cures. Polyurethane glue expands to three or four times its initial thickness, said Danielle Guido, consumer affairs specialist for Gorilla Glue. "So if you don't clamp it, it pushes the two surfaces apart."
In your case, the weight of the lamp clearly didn't provide enough clamping pressure, and the base of the lamp was probably less porous than the wood cabinet underneath. So you're left with a lamp base that didn't glue to the Lucite and with Lucite glued to the wooden cabinet. What a mess!
While the adhesive is still wet, the best way to remove excess is to just carefully wipe it away, Guido said. "It's a moisture-activated glue, so if you get it on your skin and add water, it could increase the chance of it curing on your skin." When Gorilla Glue is still wet, it can be removed using acetone, mineral spirits or paint thinner.
Dry adhesive is trickier. On the web, you'll find advice about softening polyurethane glue with denatured alcohol, acetone or more powerful organic solvents.
But once polyurethane adhesive cures, it resists the solvents that some websites say to use. Mechanical removal is the only option, Guido said.
That means cutting, scraping or grinding it away. The foamy residue is fairly easy to scrape away when it has oozed out from a joint. But in your case, you will need to cut through the adhesive that's between the plastic and the top of your cabinet, a more difficult task.
Use a thin putty knife or a razor scraper, held as flat as possible against the top of the wood. The biggest problem will be reaching deep enough to cut through all of the glue. Try to work from the center out. The kind of utility knife that has an extendible, snap-off blade might be helpful. You might need to resort to threading a hacksaw blade under the plastic and moving it back and forth to cut through the adhesive, although this is more likely to damage the top of the cabinet.
Once the plastic is off, try to cut off the remaining residue with a razor blade. You can also sand it off, using fine sandpaper and a sanding block, but this almost guarantees that you will need to refinish the top of the cabinet.
If you do damage the surface and the cabinet has a real-wood look but is actually made of material that has only a thin layer of wood with particleboard underneath, switching to a painted look might be the best option.
Or you could install new veneer over the surface, using peel-and-stick veneer. Rockler (rockler.com) sells pressure-sensitive veneers in a variety of woods and sizes, with pieces 24 inches by 32 inches costing $34.99. You would need to trim the edges carefully and then stain and finish the veneer to match the rest of your cabinet.