Do I Need to Seal a Terracotta Roof?

What Is Terra Cotta?

• The term terra cotta, which translates from Latin as “cooked earth” identifies a high-grade clay and sand mix shaped then fired for architectural or ornamental use. Sometimes ground-up fire clay is used instead of sand. Any tile made from clay gives a somewhat Spanish, rustic look to a property. For this reason terra cotta roofs are more popular in the southwestern portions of the United States. This area is also subject to extreme high temperatures. Terra cotta also is chosen for its worth in reflecting solar energy and thereby reducing cooling costs.

Deterioration in Terra Cotta

• Deterioration caused by heat and water is oddly similar; crazing and spalling both occur. Tiles that are grainy to the touch have become to some extent porous and also require rehabilitation.
  Terra cotta tiles that are not a shade of the soft, warm ruddy color associated with fired clay have been glazed. Sound glazed tiles have excellent weather-resistance. However, if the tiles’ glaze has crazed -- meaning countless tiny, random cracks have formed in the surface -- sealing is appropriate.
  Spalling describes the incremental loss of the baked clay itself, in small pieces, as flakes or as dust. Spalling typically presents as blisters if the tile surface is glazed. While crazing may not allow for increased water ingress, the friable material caused by spalling almost certainly will. Evidence of spalling is an indicator that sealing would be appropriate.

Terra Cotta and the Sealing Process

• Sealing can improve aesthetic appearance enormously, renewing color and discouraging the growth of moss and mold. Furthermore, roof sealing can increase the resale value of a property and, potentially, reduce insurance premiums.
  Reglazing of terra cotta tiles is not possible. Glazing is part of the process of firing raw clay; once the clay has been fired, it cannot be fired again. Replacement or sealing are the only viable options. Start the sealing process by pressure washing, especially in locations prone to heavy urban soiling. Then address any revealed structural failings. Rectify the faults that have led the tile to require attention; solar radiation cannot be stopped, but water incursion -- for instance through deteriorated caulking or flashing -- can. Prime, then use a high-build filler before applying at least two coats of sealant.
  It is a good idea to treat a few additional tiles with the same product and number of applications, then store the spares somewhere safe. If replacement tiles are needed in the future, they will match the rest of the roof.

The Value of Professional Help

• Having roofing professionals work on your roof can also reveal pre-existing faults that need attention. Sagging areas not visible from ground level can indicate batten damage; broken tiles can be replaced; loose cement in ridges and gables can be addressed; and loose flashing in gullies can be refitted.