Waterproofing Masonry Joints Using Molten Lead, Lead Wool Or A Proprietary Lead Cap System

CSI Division
Division 4- Masonry
Section
Masonry Restoration
Last Modified

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Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.

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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.

THIS PROCEDURE USES LEAD, A HIGHLY TOXIC SUBSTANCE. THE WORKPLACE MUST BE ADEQUATELY PROTECTED TO PREVENT INGESTION OF LEAD BY WORKERS, OR THE SPREAD OF LEAD BEYOND THE WORK SITE. ALL ENVIRONMENTAL LAWS MUST BE FOLLOWED CONCERNING CLEAN-UP AND DISPOSAL OF WASTE MATERIALS.

PART 1–GENERAL

1.01 SUMMARY

  1. This procedure provides guidance on waterproofing masonry joints using molten lead, lead wool (similar to steel wool), or a proprietary lead capping system which uses appropriate caulks or sealants.
    1. Leading joints is a traditional technique of filling joints to obtain the maximum possible waterproofing.
    2. Molten lead and lead wool are often called lead caulk.
  2. Leading, in one of these three forms, is most commonly found, and appropriately used for:
    1. Joints between stone units in the same plane, i.e. coping joints and balustrades; cross joints on cornices and belt courses; top joints on window and door lintels, entrance porticos, brackets, pilasters, watertables and any other piece of masonry which projects beyond the face of the building.
    2. Joints between stone units set approximately at right angles to each other, i.e. at parapet or side walls, or at stair risers and treads.
    3. Expansion and control joints.
    4. Anchor holes, i.e. iron fence members into masonry or concrete.
    5. Reglets - horizontal reglets generally filled with molten lead, vertical generally with lead wool. (Molten lead should NOT used where lead wedges are also used to help secure flashing into reglet.)
  3. Safety Precautions: Provide protective clothing to workers to protect them from extremely high temperatures of molten lead.
  4. 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).

PART 2–PRODUCTS

2.01 MANUFACTURERS

  1. Weathercap, Inc. www.weathercap.net/
  2. Nuclead nuclead.com/
  3. Dow Corning Corporation www.dowcorning.com
  4. GE Silicones www.ge.com
  5. H.B. Fuller Automotive Technical Systems www.hbfuller.com

2.02 MATERIALS

  1. Pure Lead: Available in 5-lb. bars at plumbing supply centers (NOT hardware superstores).
  2. Lead Wool: Available at plumbing supply centers.
  3. “Weathercap Type A (Flat) or Type B (90o Cove) Cap” as required by joint being sealed, or approved equal.
  4. Exterior grade caulk as appropriate for type of joint being sealed (for use with Weathercap or Nuclead), such as “Corning 790” or “Corning 791” (Dow Corning), “Ultraglaze 400” or “”Silpruf 2000” (GE Silicones), “PTI 738”, “PTI 707” or “PTI 7130” (H.B. Fuller Automotive Technical Systems), or approved equal.

2.03 EQUIPMENT

  1. Heat-proof crucible and source of heat to bring solid lead to melting point of 621degrees F (320 degrees C).
  2. Ladle to pour molten lead into joint.
  3. Hammer and chisels (variety of sizes) for packing lead wool into joints.
  4. Hack saw (18T x 12 inch. blade), pliers and clippers to cut, notch and bend lead cap as required by installation.

PART 3–EXECUTION

3.01 PREPARATION

  1. Protection:
    1. Work must be done on a warm day, while the masonry itself is warm, so that extreme high temperature of molten lead does not cause masonry to crack.
    2. Make sure masonry is completely dry.
    3. If using proprietary capping system, measure width of joint to determine width of cap required. Width required equals measurement of joint opening, plus the maximum percentage of joint movement experienced per scribe test, plus 1/4-inch.

3.02 ERECTION, INSTALLATION, APPLICATION

  1. Waterproofing with Molten Lead (horizontal joints only) and Lead Wool:
    1. Rake and clean joints of all loose mortar and debris.
    2. For long joints or reglets into which molten lead is to be poured, temporarily plug ends with heat resistant material.
    3. Pour molten lead, or pack lead wool tightly, into joint to seal. If molten lead is being used to waterproof the joint between a stone base and an iron picket or newel, make sure bottom of hole has lead in it before setting iron piece.
  2. Waterproofing Using a Proprietary Lead Capping System:
    1. Rake and clean joint(s).
    2. Mark off width of cap onto masonry.
    3. Apply 1-inch wide masking tape along marks.
    4. Using a clean, dry cap piece, cut, notch and/or miter sections of cap as required to fit joint.
      1. Outside angles: notch anchor shaft of cap piece a full 90 degree and bend to fit angle of masonry being sealed.
      2. Inside angle: make single cut in anchor shaft and bend to fit angle of masonry being sealed.
      3. Outside curves: notch anchor shaft at intervals to allow cap to fit curve.
      4. Inside curves: make straight cuts in anchor shaft at intervals to allow cap to fit curve.
    5. Pre-fit and contour cap after cutting or notching anchor shaft to fit joint. Lift cap out of joint and apply metal primer to cap, if required by sealant manufacturer. Allow to dry until tacky.
    6. Seat foam backer rod into masonry joint to proper compressed depth.
    7. Prime masonry if required by sealant manufacturer. Allow to dry until tacky.
    8. Apply small bead of sealant/caulk to tacky metal surface to prevent air entrapment when seated in place.
    9. Fill masonry joint to approximately 1/8-inch above face of stone with sealant/caulking compound.
    10. Set cap in place, pressing firmly into sealant/caulking compound for seating and shaping. Turn down at all angles and edges.
    11. Remove excess sealant/caulking compound with a putty knife, being careful not to get excess on masonry and leaving finished joint neat and clean.
    12. Remove masking tape.
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Last updated: Nov 7, 2023
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