Replacing Damaged Terra Cotta Units

Procedure code:
Developed For HSPG (NPS - Southeast Regional Office)
Terra Cotta Unit Masonry
Last Modified:





    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

         3.   Submittals

         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)


         1.   General:

              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
              the architect.

    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

    C.   Paint:  

         1.   "Zinc Chromate Primer" (Sherwin Williams), or
              approved equal.

         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,
              Type S

         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
              replacement pieces.


    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
                   nominal 4".

         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
                   the wall.

              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"
                   horizontal centers.  

              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".

         6.   Grouting:

              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)
                   at joints.  

              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
                   setting drawing.

              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:

         1.   Setting:

              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
                   ceramic veneer.

                   (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
                        into place.  

              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
                   setting bed.  

              d.   The combined thickness of the ceramic veneer
                   and the mortar coat, when so installed, will
                   average 1-3/4".  

              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
                   above procedure.

         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
              concave joint.  

         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
              left clean.


    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

Last Reviewed 2015-11-24