Decide whether to apply a water repellent or consolidant to historic masonry

Steps

1. Default to not applying a water-repellent coating unless there is a documented, specific water-related problem it is meant to solve, per Preservation Brief 1's general caution against routine application.
2. Rule out other causes of moisture problems first (faulty flashing, grading, gutters, open mortar joints), since a coating masks symptoms rather than fixing the underlying moisture path.
3. If a water repellent is still under consideration, test it on a sample panel and monitor vapor-permeability compatibility, since a repellent that blocks outward vapor drive can trap moisture behind the surface.
4. Distinguish a true consolidant (intended to restore cohesion to a deteriorating, friable stone matrix) from a water repellent; per Brief 1, don't assume repellents provide meaningful consolidation on their own.
5. On tax-credit or landmark projects, get the specific product and application plan reviewed and approved before application, since these coatings are difficult to reverse.