Completing a piping system requires selecting the right sealant for every penetration and
connection. This lesson covers joining consumables at a glance, thread sealants, silicone
and spray foam, and firestop products for rated penetrations.
1.4.1 — Joining Consumables: Alloys, Fillers, and Fluxes
Joining consumables must match the process and base metals, and must be applied using correct
technique — including cleaning, heat control, and post-joint inspection — to achieve
acceptable results. The table below consolidates the alloys, fillers, and fluxes covered in
earlier lessons as a quick-reference summary.
Soldering and Brazing Alloys
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95/5 Tin-Antimony (Lead-Free Solder)
Standard lead-free solder for copper tube. Melting range 232–240°C
(450–464°F). Required for potable water under OBC. Needs external paste
flux on cleaned copper. Used with air-fuel torch for joints up to ~50 mm (2 in).
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BCuP-2 / BCuP-5 (Copper-Phosphorous)
Self-fluxing on copper-to-copper; no external flux required or recommended.
Melting range ~645–815°C (1,190–1,500°F). Standard for refrigerant
copper piping. Never use on brass, bronze, or ferrous metals —
phosphorous embrittles zinc and iron alloys.
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BAg-7 / BAg-28 (Silver-Alloy)
Silver-alloy brazing filler for copper-to-copper and copper-to-dissimilar joints
(brass, steel). Requires AWS FB3-A brazing flux. BAg-7 (56% Ag) is cadmium-free and
preferred for HVAC/R. Melting range ~630–760°C (1,165–1,400°F).
More costly than BCuP; used where BCuP is prohibited.
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Welding Fillers (ER70S / E6013)
Used for structural steel welding on HVAC/R equipment frames, supports, and angle
iron. ER70S-6 is the common MIG wire for mild steel; E6013 is a common stick electrode.
Selection depends on the welding process (GMAW, SMAW), base metal, and the applicable
welding procedure specification (WPS).
Fluxes
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Flux Selection at a Glance
Soldering paste flux (water-soluble): for 95/5 solder on copper-to-copper and copper-to-brass; apply thin coat to cleaned tube and fitting cup; clean residue after soldering
Brazing flux (AWS FB3-A, white/off-white paste): required for BAg silver-alloy brazing on all joint types; active up to ~870°C (1,600°F); clean residue after joint cools
No flux (BCuP on copper-to-copper): the phosphorous in BCuP alloys is self-fluxing; adding external flux interferes with filler flow and creates unnecessary residue
Active flux for ferrous or high-zinc brass: some copper-to-steel or copper-to-high-zinc brass joints require a more aggressive flux rated for the alloy; confirm compatibility with the SDS before use
Never reuse flux from a contaminated container; once a brush has touched the copper or picked up oxide particles, the flux in the container is compromised
1.4.2 — Thread Sealants
Thread sealants fill the helical leak path created by tapered pipe threads (NPT) and
provide lubrication to prevent galling during assembly and disassembly. Selection must
consider the fluid being sealed, operating temperature, pressure, and whether the
connection will need to be disassembled for service. Applying the wrong product or
too much of the correct product can cause joint failure or system contamination.
Types of Thread Sealant
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PTFE Tape (Thread Seal Tape)
Thin polytetrafluoroethylene tape wound onto male threads before assembly.
Fills the thread helix and provides lubrication. Easy to apply, leaves no residue,
and is suitable for water, gas, and refrigerant connections where approved. Use
2–3 wraps in the direction of thread engagement (clockwise when viewed from
the end). Do not use on flare or compression fittings — tape has no place in
metal-to-metal seats.
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Thread Seal Paste (Pipe Dope)
Anaerobic or non-hardening paste applied to male threads. Provides excellent
gap-filling for course threads and uneven surfaces. Non-hardening (e.g., Rector Seal,
La-Co) remains pliable and allows disassembly; anaerobic (e.g., Loctite 565) cures
in the absence of air and locks the thread permanently. Confirm the paste is rated
for the fluid, pressure, and temperature of the specific application.
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What Not to Use
Never use PTFE tape or pipe dope on flare fittings, compression fittings, or
SAE O-ring fittings — these connections rely on metal-to-metal or elastomer-to-metal
seating; thread sealant on the seat contaminates the sealing surface and causes leaks.
Do not over-apply paste on any fitting — excess paste extruded into the pipe
bore contaminates refrigerant oil and can restrict small-bore components.
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PTFE Tape Application Procedure
Clean the male thread; remove all burrs, cutting oil, and debris before applying tape
Start the tape at the second thread from the end (leaving the first thread bare improves initial thread engagement) and wrap tightly in the direction threads will be engaged — clockwise as viewed from the thread end
Apply 2–3 wraps for standard threads; 3–4 wraps for gas lines where code requires it; overlap each wrap by half the tape width
Stretch the tape slightly as you wrap to seat it into the thread profile; finish by tearing cleanly and pressing the end down
Do not use yellow (gas-rated) PTFE tape on water connections, or white (water-rated) PTFE tape on gas lines; the density and thickness differ and are rated for different pressures
1.4.3 — Silicone and Spray Foam Sealants
Silicone and spray foam sealants are used to seal penetrations, gaps, and openings in
building envelopes, ductwork, and equipment enclosures. Each product has a distinct
purpose, and selection must account for temperature, exposure, movement, and whether
the location is subject to building code requirements for air sealing or vapour control.
Silicone Sealant
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General-Purpose Silicone
A flexible, waterproof elastomeric sealant suitable for sealing around pipe penetrations
through walls and floors where fire-rating is not required, sealing equipment cabinets,
and weatherproofing outdoor refrigerant line set penetrations. Service range typically
−55°C to +260°C (−65°F to +500°F). Paintable grades are
available; standard acetoxy-cure silicone is not paintable and has a vinegar smell during cure.
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High-Temperature Silicone
Formulated for surfaces that exceed general-purpose temperature limits; used around
flue pipes, heat exchangers, and boiler connections. Red or grey in colour. Read the
product datasheet to confirm the maximum continuous service temperature — ratings
vary by formulation (some up to 315°C / 600°F). Do not substitute high-temp
silicone for a listed firestop product; high-temp silicone is not a firestop material.
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Application Notes
Silicone requires a clean, dry surface for adhesion; wipe with isopropyl alcohol
and allow to dry before applying. Cut the nozzle at a 45° angle to match the joint
width; tool the bead before skinning begins (5–10 minutes after application in
typical conditions). Do not apply silicone over existing silicone without full removal
of the old material — adhesion to cured silicone is poor.
Spray Foam Sealant
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Uses, Limitations, and Safety
Purpose: single-component polyurethane foam used to fill irregular gaps around pipe penetrations, seal between insulation and framing, and air-seal service penetrations where fire-rating is not required
Straw foam (low-expansion): preferred around pipe penetrations; low-expansion formula minimizes pressure on rigid pipe or conduit inside the opening; high-expansion foam can bow framing and compress insulation
Fire-rated foam: where a fire-rated assembly is penetrated, a listed intumescent foam (that expands under heat to seal the opening) must be used — standard polyurethane foam is combustible and is not an acceptable firestop in rated assemblies
Skin protection: uncured polyurethane foam bonds permanently to skin; wear nitrile gloves during application; remove uncured foam with acetone, not water; cured foam can only be removed mechanically
Vapour barrier: foam is an effective vapour retarder where required; confirm compatibility with the overall vapour barrier strategy for the building envelope
1.4.4 — Firestop Sealants and Penetration Seals
Wherever a pipe, refrigerant line set, or conduit passes through a fire-rated wall, floor,
or ceiling assembly, the penetration must be sealed with a listed firestop system to restore
the fire-resistance rating of the assembly. This is a building code requirement under the
Ontario Building Code and the National Building Code of Canada — failure to firestop
rated penetrations is a code violation that exposes the occupants to increased fire spread
risk and creates a liability for the contractor.
Firestop Product Types
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Intumescent Firestop Sealant
A caulk-like product that expands rapidly when exposed to heat (typically above
150°C / 300°F), sealing the annular space around a pipe. Available in acrylic
or silicone base. Applied from a caulking gun into the annular gap between the pipe
and the sleeve or opening. Suitable for metallic pipes, rigid plastic pipes, and
multi-trade penetrations.
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Intumescent Firestop Collar
A prefabricated collar containing intumescent material that is secured around a
plastic pipe penetration. When fire melts the plastic pipe, the collar expands inward
and seals the opening before flame can pass through. Required for combustible plastic
pipes (PVC, CPVC, ABS) in fire-rated assemblies where sealant alone is insufficient
to close the annular gap left by a melted pipe.
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Firestop Mortar and Putty
Mineral-based firestop mortar or flexible putty pads used to seal large openings,
cable trays, and multi-pipe penetrations. Mortar is mixed and trowelled into the
opening; putty is pre-formed and hand-pressed around cables and pipes. Both products
resist fire and smoke and are non-combustible. Suited to retrofits where sealant
cannot fill a large annular space.
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Firestop Installation Requirements
Use only listed firestop systems — a system that has been tested and certified to a specific fire-resistance rating (e.g., UL 1479 or ULC S115) for the combination of wall/floor assembly, pipe material, and pipe size
The firestop system selected must match the actual penetration conditions: assembly type (concrete, gypsum board, masonry), pipe material (copper, steel, PVC), pipe diameter, and annular space dimension
Follow the manufacturer’s installation instructions exactly — depth of sealant, sleeve requirements, and clamping details are all part of the listed system; deviating from the listed installation voids the listing
Mark or document all firestop installations; building inspectors and fire marshals may require identification of the firestop product used at each penetration
Do not disturb or penetrate a completed firestop installation without re-sealing with a listed system; a single unsealed opening can negate the fire separation provided by the entire assembly
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Standard Silicone and Spray Foam Are Not Firestop Products
General-purpose silicone and standard polyurethane spray foam are combustible and
provide no fire resistance. They cannot be substituted for a listed firestop product
in a fire-rated assembly — even if they physically fill the gap. If in doubt
whether an assembly is fire-rated, consult the drawings or the building authority
having jurisdiction before sealing the penetration.