Like everything old, hydraulic mortars are new again, finding a place in historic restorations.

Millions of dollars are spent each year on repointing mortar and associated masonry repairs to old commercial and residential buildings in Toronto's predominately brick 19th century inner city.

As part of a multiyear restoration of the complex, work on the 74-year-old Peace Tower was completed in 1996, and a 3-year restoration is in progress for the older Library of Parliament, which opened in 1876. Hydraulic line mortar was used to restore the Peace Tower and now is specified for the Library. Both buildings originally used hydrated lime.

The masonry industry has learned from its mistakes and now looks to repointing and repairing historic masonry structures with mortars that are similar, or at least equivalent, to the original hydrated lime mortars.

While proponents say hydraulic mortars have proven themselves in Europe and have earned a place in North American masonry buildings, critics claim that hydraulic mortars have not undergone comprehensive testing in North America.

A mistake contractors make when using lime-based mortar, be it hydraulic or hydrated, is to apply it too late in the building season.

One deterrent to hydraulic mortar it is price. It costs up to five times more than hydrated line mortars.