How to Use Miter Bolts With Countertops

C.L. Rease

Miter bolts tighten and add strength to two pieces of countertop that each have a factory cut 22.5- or 45-degree mitered cut. The amount of miter bolts required to connect the miter varies by manufacturer. Each miter bolt rests in a recessed area referred to as a mortise.

Both countertops that comprise the mitered corner will have matching mortises for the miter bolts. Once the miter bolts are in place and tightened, the miter joint will be strong and secure.

  1. Align the two mitered sections of countertop. Push them together, but leave roughly 1 inch between the pieces.

  2. Insert the tube of waterproof adhesive into the drop-in caulk gun. Cut the nozzle of the adhesive on a 45-degree angle with a 1/8- to 3/16-inch opening with the utility knife.

  3. Run a small bead of adhesive 1/4 inch from the top edge of the miter on one of the pieces of countertop. On the other mitered countertop, run the bead of adhesive 1/4 inch from the bottom edge.

  4. Slide the two pieces of countertop together. Make the seam as tight as possible.

  5. Loosely install the miter bolts from underneath the countertop. Start with the miter bolt toward the back corner of the miter, and work your way forward, placing each miter bolt into the corresponding mortise cut into the countertop.

  6. Tighten the rear miter bolt, putting slight pressure on the miter joint. Perform the same procedure on the front miter bolt. Do not tighten the center miter bolts at this time.

  7. Clean any adhesive that has squeezed out from the miter joint and onto the surface of the countertop.

  8. Run your hand across the miter seam. If you have an uneven seam, set the piece of scrap wood on the high side of the seam. Tap on the wood with the hammer to force the side down. Repeat this step until the seam is even from front to back.

  9. Tighten the miter bolts. Start with the rear miter bolt, then the front miter bolt, second miter bolt from the rear of the counter, and the second miter bolt from the front of the countertop last. Do not over tighten the miter bolts as this could result in the center section of the miter joint buckling up.