Waterproofing Masonry Joints Using Molten Lead, Lead Wool Or A Proprietary Lead Cap System
- Procedure code:
- Outdoor Sculpture Manual - Cpb
- Masonry Restoration
- Last Modified:
WATERPROOFING MASONRY JOINTS USING MOLTEN LEAD, LEAD WOOL OR A
PROPRIETARY LEAD CAP SYSTEM
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.
A. 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
2. Molten lead and lead wool are often called lead
B. 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
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
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.)
C. Safety Precautions: Provide protective clothing to
workers to protect them from extremely high temperatures
of molten lead.
D. 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
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. Weathercap, Inc.
C. Dow Corning Corporation
D. GE Silicones
D. H.B. Fuller Automotive Technical Systems
A. Pure Lead: Available in 5-lb. bars at plumbing supply
centers (NOT hardware superstores).
B. Lead Wool: Available at plumbing supply centers.
C. "Weathercap Type A (Flat) or Type B (90o Cove) Cap" as
required by joint being sealed, or approved equal.
D. 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
A. Heat-proof crucible and source of heat to bring solid
lead to melting point of 621degrees F (320 degrees C).
B. Ladle to pour molten lead into joint.
C. Hammer and chisels (variety of sizes) for packing lead
wool into joints.
D. Hack saw (18T x 12 inch. blade), pliers and clippers to
cut, notch and bend lead cap as required by installation.
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
A. Waterproofing with Molten Lead (horizontal joints only)
and Lead Wool:
1. Rake and clean joints of all loose mortar and
2. For long joints or reglets into which molten lead
is to be poured, temporarily plug ends with heat
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.
B. 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.
a. Outside angles: notch anchor shaft of cap
piece a full 90 degree and bend to fit angle of
masonry being sealed.
b. Inside angle: make single cut in anchor shaft
and bend to fit angle of masonry being sealed.
c. Outside curves: notch anchor shaft at
intervals to allow cap to fit curve.
d. 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
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
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.
END OF SECTION