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Historic Preservation - Technical Procedures

Spectitle:

Repairing A Wobbly Or Broken Exterior Cast Iron Newel Post

Procedure code:

0552301R

Source:

Developed For Hspg (Nps - Sero)

Division:

Metals

Section:

Iron Railings

Last Modified:

11/12/2014

Details:

Repairing A Wobbly Or Broken Exterior Cast Iron Newel Post



REPAIRING A WOBBLY OR BROKEN EXTERIOR CAST IRON NEWEL POST

 

REFERENCES:

Margot Gayle, David Look, John Waite. Metals in America's Historic Buildings. Washington,DC: National Park Service, 1995.

L. William Zahner. Architectural Metals. New York: John Wiley & Sons, 1995.

PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on repairing a wobbly or
         broken exterior cast iron newel post.  THIS TYPE OF REPAIR
         SHOULD BE PERFORMED BY A PROFESSIONAL IRONWORKER.

    B.   A wobbly newel post may be caused by water from the
         setting concrete or stone, improper setting, and/or
         joints not caulked.  

    C.   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).

    D.   For additional information on the characteristics, uses
         and problems associated with cast iron, see 05010-04-S;
         for guidance on inspecting cast iron failures, see 05010-01-S.

1.02 DELIVERY, STORAGE, AND HANDLING

    A.   Storage and Protection:

         1.   Cast iron railing or balustrade should be stored as
              to protect from surface damage at all times,
              carefully packed and should remain so from the time
              of delivery until set.  Keep uninstalled and
              unpainted metal materials in a dry, rust-free
              storage facility; surfaces to be welded are
              generally not primed.

         2.   Salvaged historic material shall be carefully
              packed and stored under cover and in the building
              away from working or traffic areas. Mark salvaged
              material with the year of removal.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Molten lead or lead wool

    B.   Screws and bolts

    C.   Wiping cloths

2.02 EQUIPMENT

    A.   Wire brush - removes rust and flaking metal as well as
         loosened paint

    B.   Eye and skin protection

    C.   Heavy gloves and protective gear

    D.   Screwdriver

    E.   Welding equipment

    F.   Electric drill

    G.   Electric grinder


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Before proceeding with steps to repair cast-iron newel
         post, it is important to first determine the cause and
         extent of the problem.  Determine the age of the
         railing/balustrade and examine the condition of the
         entire surface.  Inspect for:

         1.   Joints - which are open or misaligned, thus
              allowing water into the railing or newel.

         2.   Parts - which have failed or which are unsecured,
              broken, cracked, missing, distorted, or loose
              (check screws and bolts).

         3.   Paint - coating failures such as chips, losses,
              peeling, checks, bubbling, and wear.

         4.   Rust corrosion - caused by moisture including, sea
              water and sea air, deicing salts, acids and some
              soils.

         5.   Galvanic corrosion - corrosion caused when iron is
              in direct contact with a dissimilar metal and is
              wetted by rain, fog, condensation, etc.

         6.   Determine the source of the moisture which causes
              the deterioration.

         7.   Determine if the railing/balustrade can be
              salvaged.

         8.   Measure the dimensions of the various metal parts
              needing replacement.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   Repairing A Wobbly Newel Post:  This can usually be
         repaired on site by a professional or in the shop by an
         ironworker.  

         1.   Reset the center rod in the base and weld small
              supports at the base of the newel.  

         2.   Drill holes in the masonry step or walk to
              correspond with the supports.  

         3.   Pour molten lead into the holes before setting the
              newel.

         4.   Caulk all the joints and prime and paint the entire
              assembly.  See 05010-13-S and 09900-07-S for
              guidance on painting cast iron.

              NOTE:  IRON THAT IS SET IN CONCRETE OR STONE SHOULD
              BE PACKED IN LEAD TO PREVENT THE IRON FROM RUSTING.
              LEAD IS SOFT ENOUGH TO STILL ALLOW THE IRON TO
              MOVE.

    B.   Repairing Posts That Are Broken in Half:  The posts must
         first be internally reinforced with steel pipes.

         1.   Before attaching the elements, clean the surface of
              any traces of dirt, oil/grease stains, peeling
              paint, or rust.  See 05010-05-R for guidance on
              cleaning cast iron.

         2.   Weld the original elements of the posts back
              together, using a professional welder.  Grind down
              any visible beads of welding material.

              NOTE:  SUCCESSFUL WELDING OF CAST IRON CAN BE A
              RELATIVELY EXPENSIVE OPERATION.

              NOTE:  WELDING OF CAST IRON IS VERY DIFFICULT TO DO
              IN THE FIELD.  IT SHOULD BE EXECUTED ONLY BY A
              SKILLED WELDER UNDER CAREFUL SUPERVISION.

              CAUTION:  DURING WELDING THE METAL BECOMES VERY HOT
              AND CAN UNDERGO TREMENDOUS THERMAL SHOCK.  IT MAY
              RECRYSTALLIZE IF EXCESSIVE HEAT IS APPLIED.  

              a.   For large sections, welding should take place
                   off site.  The piece must be removed and
                   transported  to a workshop where it can be
                   preheated before welding and postheated after
                   welding to ensure a gradual temperature change
                   within the metal.  

              b.   Advantages of welding:

                   1)   Arc welding produces a strong, durable
                        connection and, if properly executed, is
                        at least as strong as the surrounding
                        metal.  

                   2)   It is faster and less expensive than
                        threaded connections, which require
                        drilling a pilot and then tapping to
                        accommodate screws or bolts.  

                   3)   Welding is the most preferred for the
                        attachment of the decorative castings and
                        for other non-structural repairs for
                        economic reasons and because it allows to
                        preserve the original damaged elements,
                        which otherwise would have to be
                        replaced.

              c.   Disadvantages of welding:

                   1)   In cases where the original attachments
                        are bolted, the use of this method may
                        result in internal stresses (welds cannot
                        move with seasonal expansion/ contraction
                        cycles) which may in turn lead to further
                        breaks.

                   2)   Welding may leave a 'bead' along the
                        surface of the connection which may be
                        unacceptable in some restoration
                        projects, even though much of the weld
                        may later be ground down, depending on
                        the location and the welding material.

                   3)   Metallic bond (gas) welding is more
                        reliable than fusion (arc) welding in
                        repairing large sections of cast iron,
                        because a lower temperature is used and
                        heat is applied and removed at a slower
                        rate.  

                         END OF SECTION
 


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