Why does new trim look wavy on my Nepean walls?

Wavy trim can come from the wall behind it, the fitting or the stock itself, and a carpenter checks all three.

Older plaster-and-lath walls can bow and belly between studs. When a straight piece of trim is nailed across an uneven surface, it follows the high spots and bridges the low ones, and the gap or curve becomes visible once the caulk dries and the paint goes on.

A few things a carpenter checks when trim looks wavy:

• Whether the wall was scribed or back-cut to follow the surface before the trim went up
• Whether the nails hit solid framing, which affects how firmly the trim pulls down
• Whether the trim stock itself had a bow before it was installed
• Whether the reveal on a door casing is consistent, because an inconsistent reveal makes a straight piece look curved

The fix depends on what the carpenter finds. On a badly bowed wall the trim may need to be removed, the wall brought to a flatter plane, and the trim re-installed with the back edge relieved so it sits tight at the face. On a mild wave, careful nailing sequence and a flexible caulk joint can close the gap. We found no Ontario Building Code (O. Reg. 163/24) rule that sets a flatness tolerance for trim or specifies how it is fastened, and trim is on neither of the City of Ottawa's permit lists, so the standard is what looks right at a normal viewing distance.

If the trim is on an individually designated heritage property, original profiles may be a protected feature under the designation by-law, and City heritage staff should be consulted before anything is removed or replaced.

Comparing quotes? Check that each one names the same scope of work in writing, says who is responsible for any design and permit if the job grows into structural territory, lists the trim material by species and profile, and spells out what patching, caulking and clean-up are included before the painter arrives.