General Guidelines For The Repair Of Sheet Metal Aluminum Features
- Procedure code:
- Developed For Hspg (Nps - Sero)
- Metal Materials
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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
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:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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.
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
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.
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.
- For roofing over non- or poorly vented spaces, use a vapor barrier or polyethylene sheet not less than 4 mils thick.
- 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-part synthetic or rubber-base sealants. Use shall be in conformance with manufacturer's recommendations.
- 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.
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
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.
A. Surface Preparation:
- Prior to making repairs, remove all oil, dirt, and other debris from the surface.
- 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.
- 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.
- Dissimilar metals: To prevent galvanic corrosion from occurring, aluminum in contact with dissimilar metals shall be protected by a
- non-absorptive, insulative coating.
- 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.
- For repairs to aluminum sheet metal roofs and flashing, follow recommendations of the aluminum association. See also the following procedures:
- 07602-01-R, "Repairing Pinch Cracks in Long Copper Gutters".
- 07610-02-R, "Installing a Transverse Expansion Joint in a Standing Seam Copper Sheetmetal Roof".
- 07610-03-R, "Repairing a Bowing Sheetmetal Roof".
- 07610-04-R, "Repairing a Wind-damaged Copper Sheetmetal Roof Ridge and Installing a New Ridge Cap".
- 07620-02-R, "Repairing Chimney Flashing".
B. For Brazing:
- For temperatures above 8400F, brazing must be done under shop conditions only by an experienced craftsperson.
- 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.
- 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.
- Use gas tungsten-arc or gas metal-arc welding processes only.
- 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.
- Use materials and methods that minimize distortion and develop strength and corrosion resistance of base metals.
- Obtain fusion without undercut or overlap.
- Remove welding flux immediately.
- 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.
- Advantages of welding:
- Arc welding produces a strong, durable connection and, if properly executed, is at least as strong as the surrounding metal.
- It is faster and less expensive than threaded connections, which require drilling a pilot and then tapping to accommodate screws or bolts.
- 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.
- Disadvantages of welding:
- 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.
- 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.
- Use ONLY under shop conditions to insure complete removal of corrosive fluxes.
- 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.