Brick repointing questions, answered straight.

Run a key along the joint. If mortar crumbles out or the key catches more than a few millimetres in, the joint is open enough to admit water. Visible recessing from the brick face, dark staining in the joints after rain, white salt deposits (efflorescence) on the brick face, and interior dampness on an exterior wall are all signs the joints are failing. Hairline surface cracks alone are not necessarily an emergency but are worth watching.

On pre-1960 soft-fired brick, yes. It is probably the most important decision in the job. Hard Portland cement mortar is stiffer than the brick it is repointing. When the wall expands and contracts through freeze-thaw cycles, the strain goes into the brick face, which spalls. The damage to the brick is generally permanent. The mortar can be replaced again; the brick face cannot. Ask the contractor to confirm the lime versus Portland decision based on your specific brick before any joints are raked.

Water gets in and the freeze-thaw cycle does the rest. Each winter the water in the open joint freezes, expands, and widens the gap. On a typical Niagara winter with dozens of freeze-thaw cycles, a joint that is a few millimetres open in October can be significantly worse by April. Eventually the brick face spalls or the wall begins to shift at structural ties. Early repointing is always less expensive than late repointing.

April through October is the safe window. The Building Code puts a legal floor under the season: Article 9.20.14.1 requires mortar and masonry to be maintained at not below 5 degrees C during installation and for not less than 48 hours after, with no frozen material in the mix, and 9.20.14.2 requires the top of uncompleted masonry to be covered with a waterproofing material whenever work is not in progress. That period is a temperature rule, not a keep-it-dry rule, and a contractor can meet it outside the natural season with tenting and heat. St. Catharines benefits from Lake Ontario moderation, so the shoulder seasons are sometimes workable. The calendar typically fills in May and June as homeowners act on what they noticed over winter, so reaching out early in the season generally gets a better date in the core summer window.

Efflorescence, the white salt deposits on brick faces, means water is moving through the wall. Cleaning the surface addresses the cosmetic problem; finding and closing the path the water is taking addresses the real one. On a house where the mortar joints are deteriorated, the joints are usually the path. A good contractor checks the joints first on every efflorescence call before recommending surface treatment. Treating the surface without fixing the joints is a temporary answer.

No verified Niagara or Ontario figure for what this costs exists in any authoritative source, so this guide does not give one. Ask for a written, itemized quote from a local masonry contractor (there is no provincial licence for this trade), and a second one itemized the same way, so the two can be compared line by line.