How to Install Exterior Trim Around a Stone Chimney

In this video, This Old House general contractor Tom Silva shows how to custom-fit PVC trim to a stone surface.

Steps for installing exterior trim around a chimney

1. Measure 1 inch from the edge of a length of 5/4 x 5-inch PVC trim and draw a pencil line.
2. Hold the trim board against the stone chimney and use a 4-foot level to ensure it’s plumb.
3. Spread the legs on pencil scribers to span from the pencil line to the nearest stone on the chimney. Lock the scribers.
4. Use the scribers to follow the stone profile, transferring the irregular line from the chimney to the PVC trim board.
5. Adjust the bevel angle on a jigsaw to 45 degrees, and cut the PVC trim board along the scribed line.
6. Hold the trim board in place against the chimney and check its fit. If necessary, use the jigsaw to fine-tune the cut.
7. If there’s any mortar protruding from the chimney, chip it off with a hammer and cold chisel.
8. 8. Staple a 6-inch-wide strip of 15-pound builders paper to the house right beside the chimney.
9. Run a thick bead of acrylic-latex caulk onto the stone close to the house.
10. Press the scribed PVC trim board into the caulk and tight to the stone. Fasten the trim board to the house with 2½-inch-long siding nails.
11. Run a thick bead of caulk along the upper, angled portion of the stone chimney.
12. Bend a length of lead flashing to 90 degrees, then press it down into the caulk and hand-form it tight to the stone.
13. Set PVC trim on top of the lead flashing and nail it to the house.
14. At the upper, vertical section of chimney, cut a straight line along the stone using a circular saw equipped with a diamond-impregnated blade.
15. Chip away the waste stone from the saw cut with a hammer and cold chisel.
16. Screw together two pieces of PVC trim to fill the gap between the chimney and house. If necessary, rip the trim pieces to width on the table saw before screwing them together.
17. Push the L-shaped piece of trim into the space between the chimney and house. Secure with 2½-inch-long screws.

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