Replacing Damaged Terra Cotta Units
- Procedure code:
- Developed For HSPG (NPS - Southeast Regional Office)
- Terra Cotta Unit Masonry
- Last Modified:
REPLACING DAMAGED TERRA COTTA UNITS
THIS PROCEDURE SHOULD BE PERFORMED UNDER THE DIRECTION OF AN
HISTORICAL ARCHITECT OR ENGINEER TO DETERMINE THE MOST EFFICIENT
AND LEAST DESTRUCTIVE MANNER FOR EXECUTING THE WORK. APPROVAL
THE REGIONAL HISTORIC PRESERVATION OFFICER IS REQUIRED.
A. This procedure includes guidance on removing and
replacing severely damaged ceramic veneer, both adhesion
type and anchor type. Sculptural elements are not
covered in this procedure.
B. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. American Society for Testing and Materials (ASTM),
A. Shop Drawings:
1. The historical architect shall furnish all
drawings, details and other information, including
structural drawings, necessary for the manufacture
of replacement material.
2. Shop drawings showing details of construction and
jointing of replacement material shall be submitted
by the manufacturer to the contractor for approval
by the RHPO before any of the material is
processed. Drawings shall show sections,
dimensions, and the connection with other work.
(If anchored, the typical and special anchors,
grooves, etc., shall be shown.)
3. The manufacturer shall complete setting drawings,
numbered and marked to correspond with numbers and
other marks on the replacement pieces. These
drawings shall also show all other necessary data
to properly and efficiently set the material,
including dimensions and sizes of joints, anchors,
hangers, expansion and control or pressure-relieving
joints, etc., which shall be furnished by others.
A. Boston Valley Terra Cotta
B. Gladding, McBean & Co.
C. Ludowici Celadon
E. The Sherwin Williams Co.
F. Studio S Pottery
G. Superior Clay Corp.
A. Terra Cotta Replacement Units (ceramic veneer)
NOTE: ALL REPLACEMENT UNITS SHALL MATCH ORIGINAL IN SIZE
APPEARANCE, COLOR AND FINISH.
a. All materials shall be in accordance with the
architect's drawings and details.
b. All pieces shall be of even thickness
throughout, and shall be true and even on each
c. Each piece shall be thoroughly burned and free
of cracks, air bubbles and other defects.
d. All edges and details shall be crisp and
2. Adhesion Type Ceramic Veneer: Approximately 1"
thick, with ribs, grooves or dovetails on back.
Individual units shall not have a surface area
greater than 720 square feet.
3. Anchored Type Ceramic Veneer: Machine or hand
made, with a wall thickness of approximately 1-5/8"
with dovetail ribs projecting on the back.
Handmade units shall have profiles as detailed by
B. Anchoring system pieces as required - either stainless
steel, AISI (American Iron and Steel Institute) Type 316,
polyester resin, or as recommended by the ceramic veneer
1. "Zinc Chromate Primer" (Sherwin Williams), or
2. Top coat(s): Number and type of paint as
recommended by manufacturer of primer. Paint shall
be water tolerable and made by the same
Manufacturer should be same as the primer.
D. Setting Mortar:
1. 1 cu. ft. Portland Cement, ASTM C 150-67,
Type I or Type II
2. 1/2 cu. ft. approved high calcium slaked lime
putty, screened and aged at least 20 days,
containing no more than 4% magnesium oxide
3. or, 1/2 cu. ft. hydrated lime, ASTM C 206 or C 207,
4. 4 cu. ft. clean, sharp siliceous sand graded from
fine to very fine, ASTM C 144
6. 1 qt. "Hydratite Liquid" or approved equal
E. Pointing Mortar:
1. 1 vol. portland cement as above.
2. 1/4 vol. aged high calcium lime putty as above, or
3. 1/4 vol. hydrated lime as above.
4. 3 vols. very fine sand as above.
5. Gauge above with mix of one volume "Konset"
thoroughly mixed in six volumes water, or of "Anti-Hydro"
or "Suconem Red Label" or "Tricosal" or approved
equal used according to manufacturer's directions.
F. Grout Mix #1: For all vertical voids back of anchor-type
ceramic veneer and handmade ceramic veneer shall be wet
and sloppy composed of the following:
1. 1 vol. portland cement as above.
2. 3 vols. clean sharp sand as above.
3. 2 vols. top gravel, well graded from fine to
G. Grout Mix #2: For all handmade ceramic veneer sills,
copings, balusters, and rails, cornices, etc., shall be
lean and composed of the following:
1. 1 vol. portland cement as above.
2. 4 vols. clean sharp sand as above.
3. 3 vols. top gravel, well graded from fine to
H. Clean, clear potable water
A. Paint brushes
B. Hawks and trowels as required
C. Hose and spray nozzle
D. Grouting equipment
A. Surface Preparation:
1. Soak replacement pieces in a vat or box of clean
water for one hour or more just prior to
installation. The pieces should be noticeably damp
at the time of setting. Drain pieces sufficiently
to eliminate surface water.
2. At the beginning of setting each day, soak all
walls to be faced with clean water. Apply water
with a hose and spray nozzle. Soak again with
water not more than one hour before setting of
A. Removing Damaged Terra Cotta Units:
1. Remove mortar from around damaged units by hand
being careful not to chip the edges of adjacent
sound units. Insert wedges as required as mortar
removal progresses to hold damaged units in place
until they can be removed.
2. Carefully remove damaged units and all loose grout
in cavity behind unit.
B. Installing Anchored Type Ceramic Veneer:
1. Preparing the anchoring system:
a. Inspect the anchors and reinforcing armature
thoroughly for any sign of corrosion.
b. Remove any rust from anchors which can be
reused. Coat with one coat of a rust
inhibiting primer and top coat(s) of water
tolerant paint as recommended by the primer
c. Install new anchors as required and as
recommended by the ceramic veneer
2. Setting anchors and grooves:
a. The general contractor shall be guided by the
drawings for the placing of all loop-dowel
anchors or other anchors, and the provision
for the 1" x 6" horizontal grooves in the
concrete to permit the proper anchoring and
grouting of the ceramic veneer.
b. Grooves shall be 12" on vertical centers in
all spandrels and 30" elsewhere.
c. Alternate detail: 1/4" x 6" grooves
approximately 12" on vertical centers
accomplished by the use of alternate surfaced
and unsurfaced form lumber.
d. The loop-dowel anchors, or approved equal
anchors, shall be installed in vertical
alignment on about 12" centers; and shall be
spaced on equal horizontal centers of
approximately 12" but not greater than 18",
and so located, where practical, that a
vertical line of loop-dowel anchors will be
directly in back of each vertical joint of
ceramic veneer. Keep loop-dowel anchors out
of 1" x 6" horizontal grooves.
e. Dimension from face of masonry or concrete
wall to face of anchored veneer shall be a
3. Installing pencil rods:
a. Install 1/4" pencil rods vertically through
loops of loop-dowel anchors.
b. Install approximately 1" away from the face of
b. Above openings, the lower end of the pencil
rods should have 4" or more bent at right
angles over ceramic veneer soffits, and should
lie loosely thereon.
4. Installing loose anchors:
a. All loose anchors shall be located in bed
joints and/or interior webs on 12" to 18"
b. One end of each anchor shall be securely
hooked around a pencil rod, dowel rod, or
structural steel member and the other end
securely hooked into the ceramic veneer.
c. Loose anchors shall hook around 1/4" dowel
pins in joints of soffit pieces. These
anchors shall pass through loops and hook
around loop-dowel anchors.
5. Special loop-dowel anchors:
a. In deep ceramic veneer anchored soffits the
special loop-dowel anchors shall extend
vertically down to within 1" of the ceramic
veneer soffit, and shall be threaded
horizontally with 1/4 pencil rods.
b. The long dowel end of the special loop-dowel
anchor shall have 2" or more bent at right
angles and lay flat against the top of the
ceramic veneer soffit.
c. The loop ends of the special loop-dowel
anchors shall extend down vertically at least
5" from the concrete soffit.
d. Special loop-dowel anchors are to be of the
same material as the loop-dowel anchors.
e. Dimension from face of concrete soffit to face
of anchored veneer shall be a nominal 8".
a. All anchored ceramic veneer shall be set in a
full bed of mortar and all voids back of the
ceramic veneer shall be filled solid with
grout as specified under Grout Mix #1, and
shall be well rodded to eliminate all air
b. Where possible to do so, grout should be
poured to a height of 6" only behind each
continuous course of anchored ceramic veneer
and the grout allowed to set sufficiently to
"freeze" the piece in place before pouring the
balance. Grout shall have sufficient
plasticity to fill the joints from the rear.
c. All copings and cornices of handmade ceramic
veneer shall have filler pieces (grout plugs)
d. Before being set in place, all handmade
ceramic veneer copings, etc., shall be turned
bottom side up and filled solid with a lean
wet grout as specified under Grout Mix #2, and
shall later be set in place on the wall and
anchored in vertical joints as indicated on
e. Vertical joints shall be grouted solid through
openings at joints, provided in ceramic veneer
before grout plugs are placed.
f. This pre-grouting procedure is also to be used
in grilles, etc., as directed and where
required to solidly fill all voids.
B. Installing Adhesion Type Ceramic Veneer:
a. Just prior to application of mortar coats, a
limited area of the wall and the entire back
of the piece of soaked ceramic veneer about to
be set shall be given a brush coat of neat
portland cement and water.
b. Immediately thereafter spread on-half of the
mortar coat on a limited area of the wall and
the other half over the back of the piece of
(1) The mortar troweled on the back of the
piece of ceramic veneer shall be screeded
to a uniform thickness as measured from
the face of the ceramic veneer.
(2) The other half of the mortar bed applied
to the wall surface shall be screeded to
a true and plumb level.
(3) The total thickness of the mortar coat
shall average 3/4", but sufficient mortar
shall be used to create a slight excess
which will be forced out at the joints at
the edge of the piece when it is tapped
c. When the piece is set against the wall it
shall be driven home by repeated tapping with
a rubber mallet to eliminate all voids in the
d. The combined thickness of the ceramic veneer
and the mortar coat, when so installed, will
e. Minimum thickness of mortar bed shall be not
less than 1/2".
f. Any piece of ceramic veneer tipped away from
the wall for readjustment or improperly set
for any reason shall immediately be removed,
cleaned of all mortar, including the wall
surface, and reset in accordance with the
2. Soffits: Each piece of ceramic veneer, in addition
to the usual centers and wooden wedges, shall be
supported by suitable bent vertical wooden shores
exerting a constant upward pressure until the
mortar coat is set for several days.
C. Tooling and pointing:
1. If pointing is not specified, all mortar joints
shall be tooled as the setting progresses to form a
2. When pointing is specified, all mortar joints shall
be raked to a depth of 1/2".
3. Before pointing, joints shall be saturated with
clean water, after which they shall be filled
solidly with pointing mortar and tooled.
4. All surplus mortar and stains shall be removed as
the setting progresses and the surface shall be
A. Wipe all excess mortar as the work progresses. Dry brush
at the end of each day's work.
B. After mortar is thoroughly set and cured, wash new
masonry surfaces, walls, sills, overhangs, etc., of all
loose mortar, and dirt with soap or washing powder
detergent and rinse thoroughly with clean water.
Abrasives or metal tools shall not be used.
END OF SECTION