How to Make a Form for a Chimney Crown

Make the Form

• 1

  Rip a 2-by-4 inch board so it has a 15-degree bevel on one edge. Nail the 2-by-4 to a 1-by-6 board. The square edge of the 2-by-4 should be flush with the bottom of the 2-by-6.

• 2

  Cut this piece into four sections with mitered corners so they fit snugly around the top layer of chimney bricks. The beveled edges should fit together. This will make a 2-inch-thick crown.

• 3

  Drill two holes at the ends of the mitered sections. Screw them together.

• 4

  Drive two duplex nails into each section at an angle so their tips barely graze the top of the bevel. A duplex nail has a collar so you can’t drive it in all the way, and it is easy to remove.

• 5

  Oil the inside of the form. The oil will make the form easy to remove.

Install the Crown

• 6

  Mix small aggregate concrete. Hoist the concrete onto the roof in buckets

• 7

  Moisten the top of the chimney around the flue. Lay the form on top of the chimney with the beveled edge down. This will create a 1 1/2 inch drip edge when you pour the concrete.

• 8

  Strap a binder around the outside of the form to strengthen it. Fill the form with enough concrete to fill the beveled edge plus about 1 inch above the brick chimney base.

• 9

  Cut and install rebar about 2 inches from the edge of the form and between flues.

• 10

  Fill concrete to the top. Trowel a smooth top tapering to the edge. Cover the crown with plastic if the weather is hot or windy.

• 11

  Wait 24 hours. Remove the clamp and screws. Remove the form. Seal joints with caulk. Seal the crown with waterproofing.