Sealants & Waterproofing

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• No rod in half these joints, it's three-sided adhesion everywhere, that's why they're all split down the middle.

  TranslationThe installer skipped the backer rod, so the sealant bonded to the back of the joint, could not stretch and tore through its middle.

• Pull tests on the precast came back adhesive, they skipped the primer, it's R&R on the whole elevation.

  TranslationAdhesion tests showed the sealant peeling cleanly off the concrete because no primer was used, so every joint on that side must be cut out and resealed.

• Positive side is backfilled, so it's injection and crystalline from the negative side.

  TranslationThe outside of the foundation wall can no longer be reached, so the leak will be fixed from inside with resin injection and a crystalline coating.

• Through-wall flashing has no end dams and the weeps are full of mortar droppings, no wonder it's a leaker.

  TranslationThe masonry wall's internal flashing lets water run off its ends and the drainage openings are blocked, so water is getting inside.

• Wrap's reverse lapped at the sill pan, cut it and lap it right or every window on the stack will leak.

  TranslationThe weather barrier was overlapped the wrong way at the window base, so it has to be cut and relapped so water sheds outward over the flashing.

• Owner won't pay for R&R this year, so band-aid the worst drops and we'll come back in spring.

  TranslationThere is no budget to cut out and replace the failed sealant, so the worst sections will get a sealant band over the old joints as a temporary repair.

• Fill the bugholes before you spray or the concrete will outgas through the fluid-applied and you'll be chasing holidays all week.

  TranslationPatch the concrete surface voids first, or trapped air will blow pinholes through the liquid membrane that then have to be found and repaired.

Joint types, backer materials and the geometry that lets sealant stretch without failing.

• Backer rodalso backer, rod
  A round foam cord pushed into a joint to set sealant depth and keep the sealant from bonding to the back.
• Band-aidalso band-aid joint, overband
  A bridge joint applied over an existing sealant joint as a repair, without removing the old material. Shop talk
• Bond breakeralso bond breaker tape, bond-breaker tape
  A tape or material at the back of a joint that sealant will not stick to, preventing three-sided adhesion.
• Bridge jointalso bridge seal, overband
  A band of sealant laid over the face of a joint, bonding to the surfaces on either side instead of filling the gap.
• Cold jointalso pour joint
  The seam where one concrete pour meets a later one, a classic leak path in below-grade walls and slabs.
• Control jointalso contraction joint, CJ
  A cut or formed groove that makes concrete or masonry crack in a straight, planned line instead of randomly.
• Expansion jointalso movement joint, EJ
  A designed gap between building elements that lets them move with temperature, settlement and load without cracking.
• Fillet jointalso fillet bead, angle joint
  A triangular sealant bead run into an inside corner where two surfaces meet at an angle.
• Hourglass profilealso hourglass shape, hourglass joint
  The ideal cross-section of a sealant joint: thick at both bond faces and thinner in the middle.
• Movement capabilityalso joint movement capability, movement class
  How far a sealant can stretch and compress, as a percentage of joint width, while keeping its seal.
• Precompressed foamalso expanding foam tape, impregnated foam
  Impregnated open-cell foam supplied squeezed flat that slowly expands to fill and seal a joint.
• Roddingalso rod, rod the joint
  Installing backer rod into joints ahead of the sealant crew. Shop talk
• Three-sided adhesionalso 3-sided adhesion, three-point adhesion
  Sealant bonded to both joint faces and the back of the joint, which locks it in place so it tears when the joint moves.
• Two-stage jointalso dual-seal joint, double seal
  A joint with an outer rain seal and an inner air seal separated by a drained cavity.
• Width-to-depth ratioalso shape factor, W:D ratio
  The proportion between a sealant joint's width and the sealant's depth, usually targeted at about 2 to 1.

Sealant chemistries, grades, properties and the packaging and guns crews use to apply them.

• Bleedalso staining, bleeding
  Staining from fluids or plasticizers that migrate out of a sealant into porous stone or masonry.
• Bulk gunalso barrel gun, sausage gun
  A barrel caulking gun filled straight from a pail or sausage rather than from a cartridge. Shop talk
• Butylalso butyl tape, PIB
  A rubber-based sealant or tape with very low vapor transmission but little movement capability.
• Caulkalso caulking, caulking compound
  Everyday word for any gun-applied gap filler; in the trade, a lower-movement material than a true sealant. Shop talk
• Modulusalso secant modulus
  How stiff a cured sealant is, meaning how much force it pulls on its bond faces when stretched.
• Non-sagalso NS, gun grade
  Describing a sealant thick enough to stay in vertical and overhead joints without slumping.
• Painter's caulkalso acrylic latex caulk, latex caulk
  Acrylic latex caulk used to fill interior trim gaps for painting, with little movement capability. Shop talk
• Polysulfidealso Thiokol, PS sealant
  An elastomeric sealant, usually two-part, chosen for joints exposed to fuel, chemicals or constant immersion.
• Polyurethane sealantalso urethane, PU sealant
  A tough, paintable elastomeric sealant used widely on concrete, masonry and traffic joints.
• Sausagealso sausage pack, foil pack
  A soft foil or film tube of sealant loaded into a barrel gun, used instead of rigid cartridges on big jobs. Shop talk
• Sealantalso elastomeric sealant, joint sealant
  A material that fills a joint or gap to stop water and air, while accommodating movement.
• Siliconealso silicone sealant
  A sealant with a silicon-oxygen backbone, prized for UV resistance and high movement capability.
• Skin timealso skinning time, tooling time
  How long after application a sealant forms a surface skin, which ends the window for tooling.
• STPEalso hybrid sealant, MS polymer
  Silyl-terminated polyether, a moisture-curing hybrid sealant that is paintable, weather-resistant and free of isocyanates.

Foundation, blindside and deck waterproofing, membranes, protection, drainage and leak detection.

• Bathtubalso tub, full wrap
  A fully wrapped below-grade waterproofing system that encloses the foundation like a tub. Shop talk
• Bentonitealso bentonite clay, bentonite mat
  A sodium clay that swells into a watertight gel when wet, used in panels, mats and strips for below-grade waterproofing.
• Blindsidealso blind-side waterproofing, pre-applied membrane
  Waterproofing installed on the shoring or soil face before the wall is poured against it.
• Bugholesalso bug holes, blowholes
  Small surface voids in formed concrete left by trapped air bubbles against the formwork. Shop talk
• Covealso cant, cant strip
  A rounded or angled fillet built into an inside corner so a membrane turns the corner without bridging or tearing.
• Crack injectionalso injection, chemical grouting
  Pumping polyurethane or epoxy into a leaking concrete crack through ports to seal it from the inside.
• Crystalline waterproofingalso crystalline admixture, crystalline coating
  A cementitious treatment whose chemicals grow insoluble crystals inside concrete pores and cracks to block water.
• Dampproofingalso damp-proofing, dampproof coating
  A thin coating that slows soil moisture through a foundation wall but cannot resist water under pressure.
• Detail coatalso detailing, reinforcing coat
  An extra reinforced layer of membrane at corners, cracks, drains and penetrations before the main coat goes on.
• Drainage compositealso drain mat, drainage board
  A dimpled or ribbed plastic core with filter fabric that carries water down to drains instead of letting it sit on the membrane.
• ELDalso electronic leak detection, vector mapping
  Electronic leak detection, using a small electric current to pinpoint breaches in a membrane.
• Fishmouthalso fish mouth
  An open wrinkle at the edge of a membrane lap that forms a channel water can run into. Shop talk
• Flood testalso flood testing, ponding test
  Damming a membrane area and filling it with water for a day or more to prove it does not leak.
• Fluid-applied membranealso liquid membrane, fluid-applied waterproofing
  A liquid waterproofing applied by roller, squeegee or spray that cures into a continuous rubbery film with no laps.
• Holidayalso pinhole, skip
  A gap, pinhole or thin spot in a membrane or coating where it fails to cover the substrate.
• Hot mopalso hot mopping, hot-mopped pan
  Waterproofing built from layers of felt mopped down with hot asphalt, or the act of applying it. Shop talk
• Hot rubberized asphaltalso HRA, hot rubber
  A rubber-modified asphalt melted in a kettle and squeegeed onto decks as a thick membrane with no seams.
• Hydrostatic pressurealso hydrostatic head, head pressure
  Pressure from standing groundwater against a wall or slab, rising with the depth of water above that point.
• Negative sidealso negative-side waterproofing, dry side
  The interior face of a wall or slab, opposite the water, where waterproofing must resist water pushing it off.
• Peel-and-stickalso self-adhered membrane, SAM
  Field name for self-adhered membrane: rubberized asphalt or butyl sheet with a release liner on the back. Shop talk
• Plaza deckalso podium deck
  A waterproofed structural slab over occupied space, topped with pavers, soil, planters or a wearing slab.
• Positive sidealso positive-side waterproofing, wet side
  The face of a wall or slab that touches the water source, where waterproofing works best.
• Protection boardalso protection course, prot board
  A rigid sheet laid over a finished membrane so backfill, rebar and foot traffic cannot puncture it.
• Sheet membranealso sheet waterproofing, roll membrane
  Waterproofing supplied in rolls of factory-made sheet with a controlled thickness, joined at overlapping laps.
• Termination baralso term bar
  A flat metal or plastic strip fastened along the top edge of a membrane to clamp it to the wall.
• Waterstopalso water stop
  A strip cast into concrete joints to block water from traveling along the joint plane.

Flashings, laps, weeps, barriers and wall designs that collect water and send it back outside.

• Bootalso pipe boot, penetration boot
  A preformed or field-built collar that seals a pipe, rod or conduit where it passes through a membrane. Shop talk
• Counterflashingalso counter flashing, cap flashing
  Flashing set into the wall above a base flashing, overlapping it downward to shed water off its top edge.
• Dog earalso dog-eared corner, folded corner
  A corner of flashing or membrane folded into shape without cutting, so the corner stays watertight. Shop talk
• End damalso end dams, dam
  An upturned end at the termination of a flashing that stops water from running off the end into the wall.
• Flashingalso flash, flashings
  Thin sheet metal or membrane installed at joints and interruptions in a wall or roof to direct water back outside.
• Mortar droppingsalso droppings, cavity debris
  Mortar that falls into a masonry cavity during laying and piles up on the flashing, blocking drainage. Shop talk
• Rainscreenalso rain screen, drained and back-ventilated cladding
  A wall design with cladding held off the WRB by a vented, drained gap so water can escape and the wall can dry.
• Reverse lapalso reverse-lapped, wrong-way lap
  A lap installed the wrong way, with the lower layer over the upper, so water is channeled behind it. Shop talk
• Shingle lapalso shingle-lapped, shingling
  Overlapping layers so each upper piece lies over the one below, sending water down and out like roof shingles.
• Sill panalso pan flashing, sill flashing
  A tray of flashing under a window or door with a raised back and ends, catching any water that gets past the unit.
• Strip-inalso strip in, stripping in
  To seal the flange of a flashing or fixture to the surrounding membrane with an overlapping strip of tape or sheet. Shop talk
• Through-wall flashingalso TWF, thru-wall flashing
  Flashing that runs from the back of a masonry cavity out through the wall face to drain water outside.
• Weepalso weep hole, weeps
  An opening at the base of a wall or window system that lets collected water drain out.
• WRBalso water-resistive barrier, building wrap
  Water-resistive barrier, the layer behind cladding that sheds water that gets past the outer skin.

Glass setting, curtain wall seals, masonry repair and the access and repair methods of facade work.

• Bosun's chairalso bosun chair, boatswain's chair
  A single-person seat suspended from roof rigging, used by caulkers and restoration workers on facades. Shop talk
• Cap beadalso cap seal, capping bead
  A sealant bead on the outside face of the glass where it meets the stop or frame, sealing the glazing pocket from rain.
• Curtain wallalso CW
  A non-load-bearing exterior wall of glass and metal framing hung off the building structure floor by floor.
• Dropalso drops, stage drop
  A vertical strip of facade worked from top to bottom on one setup of a swing stage or bosun's chair. Shop talk
• Dutchmanalso dutchman repair, inset repair
  A patch of new stone, brick or wood cut and set into a damaged area of an original piece. Shop talk
• Efflorescencealso bloom, salt bloom
  White crystalline salt deposits left on masonry or concrete as water moving through it evaporates.
• Heel beadalso heel seal, heel bead seal
  A sealant bead at the inside edge of the glass where it meets the frame, forming a continuous air and water seal.
• IGUalso insulating glass, IG unit
  Insulating glass unit, two or more lites sealed around a spacer with a dry air or gas space between.
• Litealso light, pane
  A single pane or unit of glass in a window, door or curtain wall opening.
• R&Ralso remove and replace, cut out and reseal
  Remove and replace: cutting out old sealant completely and installing new sealant in the cleaned joint. Shop talk
• Repointingalso pointing, repoint
  Raking out deteriorated mortar joints in masonry and refilling them with new mortar.
• Setting blockalso setting blocks, glazing block
  A small rubber block under the bottom edge of the glass that carries its weight and keeps it off the frame.
• Spallingalso spall, spalled concrete
  Concrete, brick or stone breaking off in flakes or chunks at the surface.
• SSGalso structural glazing, structural silicone
  Structural silicone glazing, where glass is held to its frame by silicone instead of exterior caps or stops.
• Tuckpointingalso tuck pointing, tuckpoint
  Common trade name for repointing brick, though strictly it is a decorative technique with a contrasting thin joint line. Shop talk
• Water repellentalso penetrating sealer, water repellant
  A clear penetrating treatment that makes masonry and concrete shed rain while still letting vapor out.
• Wet glazingalso wet seal, wet-glazed
  Sealing glass into its frame with gun-applied sealant instead of preformed rubber gaskets.

Field and lab tests, mock-ups and the ways sealants and membranes break down.

• Adhesive failurealso adhesion loss, adhesion failure
  A sealant pulling cleanly away from one joint face, leaving the substrate bare.
• Alligatoringalso alligator cracking
  A pattern of surface cracks on aged sealant or asphalt that looks like alligator skin.
• Cohesive failurealso cohesive tear, cohesive split
  A sealant tearing apart within itself while staying stuck to both joint faces.
• Compatibility testalso compatibility testing, C1087
  A lab check that a sealant and the materials it touches do not react, discolor or lose adhesion together.
• Field adhesion testalso pull test, cut-and-pull test
  A test that cuts a tab of cured sealant from an installed joint and pulls it to see whether it lets go of the substrate.
• Hose testalso water test, spray test
  A field water test spraying a controlled stream from a calibrated nozzle at joints and windows to find leaks. Shop talk
• Leakeralso leaking unit
  Any window, joint or unit that is letting water in, as tracked on a leak investigation punch list. Shop talk
• Mock-upalso mockup
  A full-size sample of a wall, window or joint assembly built and tested before the real work starts.
• Outgassingalso out-gassing, gassing
  Gas escaping into curing sealant or membrane from punctured rod or damp concrete, leaving bubbles and pinholes.
• Reversionalso reverting
  Cured sealant breaking down and turning soft, sticky or gooey again with heat, sun or chemical attack.
• Substrate failurealso substrate cohesive failure
  The joint face itself breaking, so sealant comes away with a skin of concrete, coating or EIFS still attached.

Surface preparation, priming, tooling and removal steps that decide whether the work lasts.

• CSPalso concrete surface profile, surface profile
  Concrete surface profile, a 1 to 10 scale of how rough a prepared concrete surface is.
• Dry toolingalso dry tool
  Tooling sealant without water, soap or solvent on the tool, as most manufacturers require.
• Laitancealso cement skin, weak surface layer
  A weak, powdery skin of cement and fines on the surface of concrete that sealants and membranes cannot hold onto.
• Primeralso sealant primer, membrane primer
  A thin liquid brushed or wiped onto a joint face or deck so the sealant or membrane bonds reliably.
• Rake-outalso raking out, cut-out
  Cutting and clearing old sealant or mortar out of a joint so it can be refilled. Shop talk
• Spoonalso tooling spoon
  Caulker's word for a tooling tool, often an actual bent spoon or a spoon-shaped steel blade. Shop talk
• Toolingalso tool
  Pressing and shaping freshly applied sealant with a tool to force it against the joint faces and give it a neat profile.
• Two-rag wipealso two-cloth wipe, two-cloth method
  Cleaning a joint face with a solvent-wet cloth followed immediately by a dry cloth, before the solvent evaporates.

Frequently asked questions

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