The Secretary of the Interior's Standards for the Treatment
of Historic Properties emphasize the retention and preservation
of historic building material. Preservation and repair treatments
are always preferable to replacement.
Mortar Joint Repair. Deteriorated mortar joints and loose
mortar or grout can generally be repaired. First, the entire
floor should be checked for loose tiles that need to be regrouted.
Damaged mortar should be carefully removed by hand and the joints
wetted or a bonding agent applied in preparation for regrouting.
When making mortar repairs, it is important to use grout that
matches the old in color and consistency as closely as possible.
Tile Repair. Trying to remove one tile can endanger surrounding
tiles. Thus, it may be better to preserve and retain an original
historic tile that is only slightly damaged, rather than replace
it. Sometimes cracks may be repaired, or a corner or piece of
tile that has broken off may be re-attached, using an epoxy glue,
or grout. If a tile is chipped or a small corner or edge is missing,
a carefully executed patch of epoxy-mixed with colored enamel,
or mortar tinted to blend with the tile, may be less conspicuous
than trying to replace every tile that has even the slightest
damage. And, it is a better preservation treatment.
In limited instances, glaze failure or surface powdering of ceramic
floor tiles may sometimes be treated successfully by a conservator
with a specially formulated, solvent-based, mineral densifying
agent (such as silicic acid), followed by a siloxane sub-surface
repellent, applied 24 hours later. Under the right circumstances,
such a treatment can harden and bind the surface, and lower the
absorbency of the tile, and still maintain the vapor transmission.
But this is a highly complex undertaking and should only
be attempted by a conservator after appropriate testing. Not
only are these chemicals highly toxic and dangerous to handle,
but if used improperly, they can cause greater damage to the tile!
 This inappropriate ceramic tile repair is easy to spot. Photo: NPS files. |
Tile Replacement. When an individual tile or a larger
portion of an historic ceramic tile floor is missing or so severely
damaged that it cannot be repaired, or if it has become a safety
hazard, then it should be replaced. When a ceramic tile floor
has deteriorated as a result of long term wear and abrasion, or
from settlement or vibration damage to the setting bed, there
are a number of factors that need to be considered before choosing
a preservation treatment. If damage to tiles is the result of
more than normal wear and tear, the source of the problem needs
to be identified, and the problem corrected before replacing the
damaged tiles.
Successful replacement not only depends on the availability of
matching tiles, but on the condition of the substrate on which
the tiles are laid. Before installing the replacement tiles,
any problems, such as settlement or vibration, will have to be
addressed, and the height of the new setting bed may have to be
adjusted for the thickness of the new tiles.
Selective Replacement of Individual Tiles. This cautious
approach, typically an attempt to replace only the most seriously
damaged tiles, is often taken or considered when only a small
number of tiles are involved. Unless old, matching tiles can
be found and reused, replacement often requires specially fabricated
reproduction tiles. In some instances, individual historic tiles
that are damaged may be replaced with matching tiles salvaged
from other, less prominent areas of the floor or from other buildings.
This is most feasible if the tiles to be replaced are either
plain, and easy to match, or decorated with a common historic
floor tile pattern.
"Preserving Historic Ceramic Tile Floors" an Historic Preservation Brief
