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Historic Preservation - Technical Procedures

Spectitle:

General Guidelines For The Repair Of Sheet Metal Aluminum Features

Procedure code:

0501008R

Source:

Developed For Hspg (Nps - Sero)

Division:

Metals

Section:

Metal Materials

Last Modified:

02/24/2012

Details:

General Guidelines For The Repair Of Sheet Metal Aluminum Features



GENERAL GUIDELINES FOR THE REPAIR OF SHEET METAL ALUMINUM FEATURES


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure provides general guidelines for making
         simple repairs to aluminum features made from sheet
         metal.  These include roofing, flashing, gutters,
         downspouts and leader heads, and miscellaneous other
         rainwater goods.  For repairs to other types of aluminum
         features see procedure 05010-09-R, "General Guidelines
         for the Repair of Three-dimensional Aluminum Features."

    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).

    C.   For general information on the characteristics, uses and
         problems associated with aluminum, see 05010-08-S.

1.02 REFERENCES

    A.   Technical Report #C-6:  "Aluminum and its Alloys," The
         Aluminum Association, September 1978, fourth printing,
         February 1984.

    B.   Technical Report #35:  "Specifications for Aluminum Sheet
         Metal Work in Building Construction," The Aluminum
         Association, August 1980.

    C.   "Metal's in America's Historic Buildings:  Uses and
         Preservation Treatments", U.S. Department of Interior -
         National Park Service - Preservation Assistance Division,
         Chapters 8 and 18, Revised 1993.

    D.   Aluminum Association
         900 19th Street NW, Ste. 310
         Washington, DC  20006

1.03 MAINTENANCE

    A.   Protect aluminum architectural elements with non-
         absorptive, insulating coating to prevent direct contact
         with corrosive agents.

    B.   Protect aluminum architectural elements from rainwater
         run-off from wood and copper roofs and copper gutters.

    C.   Where concealed aluminum touches masonry, coat with a
         heavy-bodied bituminous paint followed by two coats of
         aluminum metal and masonry paint.

    D.   When aluminum is painted for cosmetic reasons and there
         is no incompatibility with other building materials,
         prime with a zinc chromate primer and apply two finish
         coats of compatible paint from the same manufacturer.  DO
         NOT USE lead-based paints or paints with copper
         containing anti-fouling agents.


PART 2---PRODUCTS

2.01 MATERIALS

    A.   Aluminum to match existing in finish, alloy (unless
         failure was caused by the use of an unsuitable alloy for
         the conditions), temper, thickness, color and appearance.

    B.   Aluminum cleats of same finish, alloy, temper, thickness,
         color and appearance as sheet goods being repaired.

    C.   Aluminum nails, screws, bolts, nuts washers, expansion
         inserts, rivets, wedges and plugs as required by repair.
         Must be of an appropriate thickness, alloy, temper, etc.,
         for intended use.

    D.   Building paper or roofing felt:  Minimum weight shall be
         15 lbs.  Papers containing additives of heavy metals or
         chemicals corrosive to aluminum shall not be used.

         1.   For roofing over non- or poorly vented spaces, use
              a vapor barrier or polyethylene sheet not less than
              4 mils thick.

         2.   For roofing over well vented spaces, use a water-
              repellent material (not necessarily water proof).

    E.   Sealants (for use with mechanical methods of joining
         sheet goods where watertightness cannot be achieved with
         a standard seam):  

         1.   1-part synthetic or rubber-base sealants.  Use
              shall be in conformance with manufacturer's
              recommendations.

         2.   2-part synthetic or rubber-base sealant.  Use shall
              be in conformance with manufacturer's
              recommendations.

    F.   Elastic cement

    G.   Paint for back painting/priming shall be bituminous paint
         of cut-back type.  Where appearance is a factor, use
         methacrylate type lacquers.

    H.   Filler as appropriate for base metal and joining
         technique being used.  Consult manufacturer.

    I.   Flux as appropriate for metal and joining technique being
         used.

2.02 EQUIPMENT

    A.   Gas tungsten-arc or gas metal-arc equipment as
         appropriate for welding repair.

    B.   Torch, iron or hot plate as appropriate for brazing
         repair.

    C.   Fire extinguisher


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Verify the aluminum type prior to the installation of
         replacement material.  Failure of feature may be the
         result of using the wrong type of alloy for the
         environmental conditions encountered.

3.02 PREPARATION

    A.   Surface Preparation:

         1.   Prior to making repairs, remove all oil, dirt, and
              other debris from the surface.

         2.   All surfaces which are to be covered with aluminum
              shall be smooth, even and free of small bumps and
              hollows.  All surfaces shall be dry both before and
              during the placing of the aluminum.

              a.   Wood:  Lumber shall be well seasoned, straight
                   and free of knotholes and splits.  All joints
                   shall be true and even and firmly attached
                   with all fastener heads flush with the top
                   surface.  All surfaces shall be covered with
                   building paper or painted with two coats of
                   any quality exterior type paint or the
                   aluminum shall be back primed.

              b.   Dissimilar metals:  To prevent galvanic
                   corrosion from occurring, aluminum in contact
                   with dissimilar metals shall be protected by a
                   non-absorptive, insulative coating.

              c.   Concrete and masonry:  These surfaces shall be
                   covered with building paper or the back side
                   of the aluminum shall be painted.  Where
                   aluminum is to be inserted into slots or
                   reglets, the slots or reglets shall be filled
                   with sealant so that the sealant covers both
                   surfaces of the aluminum in the slot or
                   reglet.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   For Mechanical Joining:  

         NOTE:  REPAIRS TO FLASHING, GUTTERS AND DOWNSPOUTS,
         ROOFING, ETC. CAN BE MADE USING STANDARD SHEET METAL
         REPAIR TECHNIQUES.  

         1.   For repairs to aluminum sheet metal roofs and
              flashing, follow recommendations of the aluminum
              association.  See also the following procedures:

              a.   07602-01-R, "Repairing Pinch Cracks in Long
                   Copper Gutters".

              b.   07610-02-R, "Installing a Transverse Expansion
                   Joint in a Standing Seam Copper Sheetmetal
                   Roof".

              c.   07610-03-R, "Repairing a Bowing Sheetmetal
                   Roof".

              d.   07610-04-R, "Repairing a Wind-damaged Copper
                   Sheetmetal Roof Ridge and Installing a New
                   Ridge Cap".

              e.   07620-02-R, "Repairing Chimney Flashing".

    B.   For Brazing:

         1.   For temperatures above 8400F, brazing must be done
              under shop conditions only by an experienced
              craftsperson.  

         2.   Use brazing only on those items where joint design
              allows for the complete removal of flux residue.

    C.   For Field Welding:  

         NOTE:  WELDING SHOULD BE EXECUTED ONLY BY A SKILLED
         WELDER UNDER CAREFUL SUPERVISION.

         NOTE:  USE CAUTION IN HANDLING FLAME TOOLS WHEN WELDING.
         THE DANGER OF SETTING THE STRUCTURE ON FIRE IS ALWAYS
         PRESENT.  COMPLY WITH FIRE, SAFETY AND ENVIRONMENTAL
         PROTECTION REGULATIONS.

         CAUTION:  DURING WELDING THE METAL BECOMES VERY HOT AND
         CAN UNDERGO TREMENDOUS THERMAL SHOCK.

         1.   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.  

         2.   Use gas tungsten-arc or gas metal-arc welding
              processes only.  

         3.   If the aluminum has anodized coating, the coating
              must first be removed from the surfaces to be
              welded to permit proper fusion of the surfaces.

         4.   Use materials and methods that minimize distortion
              and develop strength and corrosion resistance of
              base metals.

         5.   Obtain fusion without undercut or overlap.

         6.   Remove welding flux immediately.

         7.   At exposed connections, finish exposed welds and
              surfaces smooth and blended so that no roughness
              shows after finishing and contour of welded surface
              matches those adjacent.

         8    Advantages of welding:

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

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

              c.   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.

         9.   Disadvantages of welding:

              a.   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.

              b.   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.

    D.   For Oxyfuel-gas Welding:  

         NOTE:  WELDING SHOULD BE EXECUTED ONLY BY A SKILLED
         WELDER UNDER CAREFUL SUPERVISION.

         1.   Use ONLY under shop conditions to insure complete
              removal of corrosive fluxes.

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

    F.   DO NOT SOLDER ALUMINUM SHEETMETAL.

                         END OF SECTION