Urethane adhesive has the strength and durability to join just about any surface, be it wood, plastic or metal. It comes in water or oil-based formulas, with some types designed for water-resistant applications. Urethane has become popular with the wood-crafting community, where it has shown potential in joining tiles, wood panels and floor joints. The auto industry has found it performs adequately for plastic and small metal repairs, as well as some window installations and fabric repair. The use of urethane as an adhesive comes with some precautions and special procedures, since it can be very unforgiving if not applied right.
Things You'll Need
- Mixing bowl
- Mixing stick
- Putty knife
- Wood wedges
- Cinder blocks or weights
- Sandpaper (assorted grits)
- Bristol brush (stiff)
- Urethane glue (squeeze bottle or caulking gun tube)
- Dish washing soap
Applying Urethane Glue
Prepare the surface about to be glued, keeping in mind what type of material you will be bonding. Read the directions on the urethane container thoroughly, and pay strict attention to the instructions for your material type. Note the cure or drying time, mixing instructions and room temperature required.
Prepare two metal surfaces for bonding by sanding both parts of the metal surfaces with heavy, 240-grit sandpaper. Sand back and forth, using a crosshatch pattern. Follow up additional sanding with a lighter 400- or 600-grit sandpaper. Wipe the surfaces with acetone. Remove every trace of sanding residue, grease, oil or wax. Any foreign substance will contaminate the adhesive qualities of the glue.
Remove any wire brush residue from the bonding surface if, for example, you have cleaned out a window channel for the installation of auto glass. Leftover iron bristles will rust with the application of a water-base urethane and ruin the adhesive qualities.
Squeeze some urethane glue into a small mixing bowl and stir the contents with stick. Do not froth the mixture, which might introduce air bubbles.
Work a putty knife back and forth, using downward pressure. Use the putty knife to apply a thin film (coat) on both surfaces that will be joined. Smooth the surfaces, removing all air pockets and bubbles. Stick the surfaces together by hand.
Apply a clamping device to hold the pieces together, such as C-clamps, a wood wedge or weights. Apply stiff pressure on the joint to remove any trapped air because air bubbles weaken urethane bonding properties, and the glue expands when it dries. Let dry according to directions. Some oil-based urethane adhesives might take as long as three days to completely cure.
Prepare wood surfaces that will be joined by sanding both pieces, using the coarse and then fine sandpaper. Remove all sanding dust residue and any moisture that might be in or around the area. Buff it dry with a clean towel. Apply the urethane glue to both surfaces, using a putty knife to smooth out all air pockets and bubbles. Either cinch the surfaces together or use heavy weights to compress the bond. Let dry according to instructions.
Prepare plastic surfaces with coarse and fine sanding. Clean the surfaces with dishwashing soap and water. Completely dry the surfaces to remove any moisture. Apply urethane glue to both surfaces, smoothing out the glue. Clamp, wedge or weight the surfaces together and let dry according to instructions.
Remove any excess glue that has seeped out between the bonding surfaces with a putty knife. Do this quickly. If the glue has set up and dried, use the sharp end of the putty knife to chip the excess away, then wipe down any leftover film with a small amount of acetone.
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