Traffic deck waterproofing and coating field guide

Traffic coating, and why it protects the structure not just the surface

A traffic coating is an elastomeric waterproofing membrane bonded to the top of a concrete deck: a parking garage floor, a plaza or podium over occupied space, a balcony, a stadium concourse. People see the textured wear surface they walk and drive on and call it the floor finish. That is not what it is for. The job of a traffic coating is to keep water, and the chlorides dissolved in it, out of the concrete, because the deck below is structural and the water is what destroys it.

The system is built in layers, each with a job. A primer wets the concrete and grips it. A base coat, the elastomer, is the waterproofing and bridges the cracks that move. An aggregate broadcast, usually silica sand, sets into a coat to give traction and take the wear of tires and feet. A top coat locks the aggregate down and takes the UV. Miss the prep or coat a wet slab and none of the layers matter, because the whole thing lets go at the bottom.

This guide is the deck-top sibling to two others. The below-grade foundation waterproofing guide covers holding back groundwater under hydrostatic head on a wall you backfill. The low-slope roof coating restoration guide covers fluid-applied coatings that renew an aging roof. A traffic coating shares their chemistry and their failure modes, but it lives where people drive and walk, so it carries an aggregate wear course the other two do not.

Why is a traffic coating corrosion protection, not just a wear surface?

A traffic coating is corrosion protection because the thing it protects is the reinforcing steel inside the deck, not the concrete surface you can see. Concrete is strong in compression and weak in tension, so a deck is reinforced with steel, the rebar and often post-tensioning tendons, to carry the loads. Steel in sound concrete is protected by the concrete's high alkalinity, which holds a passive film on the metal. Two things break that protection: water, and the chlorides dissolved in it.

Chlorides come from road salt and deicers tracked in on tires, from marine air, sometimes from chloride accelerators used in the original concrete. When chloride-laden water reaches the steel and the concentration passes a threshold, the passive film breaks down and the steel starts to corrode. The coating's real job is to stop that water and salt at the surface so it never reaches the bar. A wear surface that holds up but leaks has failed at the only job that mattered.

Frame it for the owner the way the structural engineer does. The coating is not a floor finish you replace for looks. It is the corrosion protection on a structural element, and the cost of letting it lapse is measured in concrete repair and shored decks, not in a fresh coat. Hedge the chloride thresholds and the assessment to the engineer and the testing, because the numbers depend on the cover, the concrete, and the exposure.

How water and chloride destroy a concrete deck

The deterioration runs in a cycle, and the coating exists to break it at step one. Water carrying chloride soaks into the concrete through the pores and, faster, through every crack and joint. It reaches the reinforcing steel. The steel corrodes. Here is the mechanism that does the damage: rust occupies several times the volume of the steel it formed from, so the corroding bar swells and pushes outward on the concrete around it.

That expansion first delaminates the concrete, splitting it along the plane of the steel into a layer that sounds hollow when you sound it with a hammer or a chain drag. Then the delaminated layer breaks free and falls away, the spall, exposing the rusting bar to the open air and more water. Once a bar is exposed it corrodes faster, loses section, and the deck loses the steel it was designed around. On a post-tensioned deck a corroded tendon is worse, because it carries far more load and fails with far less warning.

Stop the water and the chloride at the surface and the cycle never starts. That is the whole argument for the coating, and it is why a coating that is worn through or split is not a cosmetic problem. It is the protection failing on a structure that keeps failing until someone pays to repair the concrete and reinstate the membrane. The below-grade guide covers the same corrosion chemistry from the other side of the structure, where the water comes from the soil instead of the road.

The traffic-coating system, layer by layer

The system is a stack of liquid-applied coats, usually one or two-component polyurethane, built up to a specified thickness over a prepared deck. Each coat has one job and the order is not negotiable. ASTM C957 is the specification that describes this family: a high-solids, cold liquid-applied elastomeric waterproofing membrane with an integral wearing surface, for decks not under hydrostatic pressure, rated for pedestrian and vehicular traffic. The base coat is named in that standard as the coat providing the primary waterproofing.

Two-component urethanes cure by reaction and set faster, which speeds the recoat between layers. One-component urethanes cure by reacting with moisture in the air and are simpler to handle. Other chemistries, polyurea, PMMA, and PUMA, show up on fast-track or heavy-duty decks where the cure speed or the chemical resistance earns them. Which chemistry and how many coats is the manufacturer's system, not a mix-and-match across brands, because the primer, base, and top are formulated to bond to each other.

The base coat: the waterproofing and the crack-bridging

The base coat is the waterproofing, full stop. It is the elastomeric urethane membrane that actually keeps the water out, and everything above it exists to protect it from traffic and sun. If the base coat is continuous, bonded, and built to thickness, the deck is waterproof. If it is thin, pinholed, or unbonded, the deck leaks no matter how good the top coat looks.

The other job of the base coat is crack-bridging. Concrete decks crack, and many of those cracks move with temperature and load. An elastomer has the elongation to stretch across a moving crack without tearing, so the membrane stays continuous while the concrete underneath opens and closes. That flexibility is the reason the system is elastomeric and not a rigid coating. The base coat carries the bulk of the specified film thickness, and on a traffic deck the manufacturer ties the mils to the traffic class.

Build it to the spec mils and confirm it as you go. A base coat applied too thin to save material is the most direct way to a leak, because it bridges less crack movement, holds less wear reserve, and pinholes where the wet film ran light. The thickness is the membrane. The roof coating guide makes the same point on a roof: the dry mils are the warranty, not where you find savings.

The aggregate broadcast: traction and the wear layer

The aggregate broadcast is what turns a waterproof membrane into a surface people can drive and walk on. It is kiln-dried silica sand, sometimes a harder specialty aggregate, broadcast into a wet coat of urethane so the grains set into the membrane and stand proud of it. The grains do two jobs. They give slip resistance, the traction a ramp or a wet pedestrian deck needs, and they take the abrasion of tires and feet so the wear hits the sand and the aggregate-rich coat instead of the waterproofing below.

The broadcast rate and the grain size come off the manufacturer's data sheet and they change with the traffic. A pedestrian deck takes a lighter broadcast for a finer texture underfoot. A vehicular deck, and especially a ramp or a turning lane, takes a heavier broadcast and often a second one in an intermediate coat, because turning tires grind the surface hardest. Broadcast to refusal where the spec calls for it, which means seeding the wet coat until it will not absorb more sand.

The embed is what makes it last. Sand thrown onto a coat that has started to skin sits on top and sweeps away under traffic. Sand broadcast into a properly wet coat is locked by the urethane around each grain and held by the top coat over it. Get the timing and the rate right and the wear surface lasts. Get it wrong and the deck polishes smooth and slick in the drive lanes first, which is also where it is most dangerous.

The top coat and the sacrificial wear surface

The top coat goes on over the aggregate and does the finishing work. It saturates and locks the broadcast sand so the grains cannot dislodge under traffic, it carries the color and the UV-stable resin that keeps the system from chalking and degrading in sunlight, and it is the sacrificial layer that wears first so the base coat does not. On many systems the top coat is an aliphatic urethane, chosen because aliphatics hold their color and resist UV better than the aromatic resins used lower in the stack.

Because the top coat is sacrificial, it is also the renewable part of the system. The maintenance recoat is a fresh top coat, and sometimes a fresh broadcast and top coat, applied before the wear reaches the aggregate and the base. The color matters more than it looks. A contrasting or line-marked top coat lets you see where traffic has worn the surface thin and where the recoat is due. Pick the top coat for the exposure, the sunlight, the tire marking, and any chemical contact, from the manufacturer's system for that base.

What is the difference between vehicular and pedestrian traffic coating?

The difference between vehicular and pedestrian traffic coating is the load the surface takes, and it drives the thickness, the aggregate, and sometimes the chemistry. A pedestrian system carries foot traffic on a balcony, a plaza, a walkway, or a stadium concourse. A vehicular system carries cars and trucks on a parking deck, a ramp, or a service route. Tires, especially turning and braking tires, grind and shear the surface far harder than feet, so the vehicular system is built heavier.

Heavier means more total dry film and more aggregate. Manufacturers commonly build pedestrian systems on the order of 20 to 35 dry mils exclusive of aggregate, and vehicular systems thicker, often around 40 to 55 dry mils, with the high end on ramps, turn radii, and drive aisles where the wear concentrates. Those ranges are typical published figures, not a standard you can cite, so pull the exact mils and broadcast rate from the system data sheet for the traffic class and the deck.

The zones inside one deck are not equal either. The drive lanes, the ramps, and the turning areas of a parking structure see the worst wear and often get the heavy vehicular build with a double broadcast, while the parking stalls can take a lighter build. Map the deck by use before you price it. The engineer and the manufacturer set the system for each zone.

How do you prepare the concrete for a traffic coating?

You prepare the concrete by mechanically cleaning and profiling it until the surface is sound, clean, and rough enough for the primer to grip, and this is the single biggest controllable failure point on the job. The coating bonds to the surface you give it. A urethane laid over laitance, curing compound, oil, dust, or an old coating bonds to that contaminant and lets go at the first stress, taking the whole system with it.

Profile means texture. The reference is the International Concrete Repair Institute's concrete surface profile, the ICRI CSP scale from 1 (smooth) to 9 (very rough), set out in ICRI Guideline 310.2. Traffic coatings commonly call for something in the CSP 3 to 4 range, achieved by shot blasting, which is the workhorse, or by grinding or scarifying on smaller and detail areas. Shot blasting strips the weak laitance and any curing compound and opens the surface pores in one pass. Confirm the required CSP against the manufacturer's system, because it varies by product.

What you remove matters as much as the profile. Laitance, the weak cement-rich film on the surface, has to come off or the coating bonds to a layer that is already loose. Curing compounds and form release have to go, because most coatings will not stick to them. Oil and tire rubber on a recoat have to be cut out. The way to settle whether the prep is good enough is not the eye, it is the adhesion test covered later. Prep is unglamorous and it is where the bond is won or lost, the same logic that governs any coating over concrete, below grade or on a floor.

Why a wet or green slab delaminates the coating

Coat a wet, green, or uncured slab and the membrane delaminates. This sits with surface prep as the top cause of traffic-coating failure, and it is worth being blunt about. New concrete has to cure and dry before the coating goes on, commonly a 28-day cure as a starting point, and just as important it has to be below the moisture limit the manufacturer sets. Cure time alone does not prove a slab is dry. A 28-day-old slab in a humid, poorly drained structure can still be wet enough to fail a coating.

The mechanism is vapor drive. Water in the slab moves toward the surface as vapor, and when a sealed coating is in the way the vapor pressure builds under the film and breaks the bond, blistering and delaminating the coating from below. The water does not have to be standing. It only has to be moving, and it moves out of any slab that has not dried.

Test it, do not guess. The common methods are the in-situ relative humidity probe, ASTM F2170, which reads moisture at depth in the slab and is the more predictive test, the calcium chloride moisture-vapor-emission test, ASTM F1869, which reads the surface, and the plastic-sheet test, ASTM D4263, as a rough field check. The pass-fail limit is the coating manufacturer's, not a universal number, so test to the method and the threshold the product calls out. On a suspended deck drying from one side, on a slab over occupied space, or on any deck poured under a tight schedule, this is the test that saves the job. Skip it and you own the delamination.

Treating the cracks before the membrane

Treat the cracks before you coat, because the coating cannot fix what it cannot bridge. The base coat has the elongation to span hairline and minor cracks that move a little, but a wider or actively moving crack telegraphs straight through a plain field coat and splits the membrane over it. So cracks get detailed first, sized and treated to what they are.

The treatment scales with the crack. Static hairline cracks may need nothing beyond the field membrane. Non-structural cracks up to a small width commonly get a detail coat, a stripe of base material run over the crack, for example on the order of 4 inches wide at a heavier wet film and centered on the crack, before the field coat goes on, so there is extra membrane and crack-bridging right where the movement is. Wider or working cracks get routed out and filled with a compatible sealant or the manufacturer's detail material, then detailed over. A moving structural crack is the engineer's call, not the applicator's, because it may signal something the coating is not meant to address.

The exact crack widths and treatments are the manufacturer's and the engineer's to set, and they vary with the system and the deck. The point in the field is simple. Walk the deck and find the cracks before the membrane, treat each to its width, and never trust the field coat to cover a crack that was left raw. The crack you skip is the line the membrane splits on later.

The detailing: coves, drains, penetrations, terminations

The field of a deck rarely leaks. The details leak: the edges, the drains, the penetrations, the joints, and the wall-to-floor corners. So the detailing is the job and the flat field is the easy part, the same truth that governs the below-grade and roof guides.

The cove is the first one. Where the deck meets a wall, a curb, or a column, the membrane has to turn up the vertical surface so water cannot run behind it at the corner. A cant or fillet at the inside corner keeps the membrane off a sharp 90 degree angle, where it would tent or thin, and the base coat carries up the wall to a defined height and terminates into a sealed reglet or under a counterflashing. Drains are next. The membrane has to tie into the drain so water sheds into it and not under it, which on many drains means dressing the membrane into the drain body or under a clamping ring so the termination is sealed and mechanical. Penetrations come after, every pipe, post, conduit, and sleeve through the deck, each with the membrane dressed up and sealed to it, often with a detail coat and reinforcement.

Detail these before you roll the field, not after. The field goes fast and the details are slow, and the schedule pressure to skip them is exactly why most deck leaks trace to a corner, a drain, or a penetration rather than the middle of a sound membrane.

Expansion joints: do not bridge them with the coating

Expansion and control joints are not details you coat over. They are designed to move, often more than any elastomer can bridge and survive, so running the traffic coating across a working expansion joint asks the membrane to do something it tears doing. The joint gets its own system: a joint sealant rated for the movement, or a dedicated expansion-joint assembly, and the traffic coating terminates into it on each side rather than spanning it.

The distinction that matters is movement. A true expansion joint accommodates structural movement and gets a movement joint system, with the sealant or assembly selected for the joint width and the expected travel. A fine control or saw-cut joint that barely moves can sometimes be filled and detailed under the coating, but only where the manufacturer and the engineer say it qualifies. When in doubt, treat it as moving. Manufacturers publish lists of joint sealants approved for use under their traffic coatings, because the sealant and the coating have to be chemically compatible or the coating will not bond over the treated joint.

Bridge a moving joint with the field coat and the failure is predictable. The membrane splits along the joint the first hot or cold day, and water pours straight into the structure at the one line you most needed sealed. Detail the joints to their movement, and let the engineer set the joint system.

Slope to drain, and why ponding kills a coating

Water has to leave the deck, and the coating does not change that. A traffic coating is waterproofing, not drainage, and a deck that ponds holds water on the membrane around the clock, soaking the details and accelerating wear and any UV or chemical attack at the low spots. Standing water also finds the one pinhole or thin spot the wet film left, where a deck that drains would have shed the water before it could.

Slope is the fix and it belongs in the design, not the coating. The deck should be sloped to the drains, commonly cited around a minimum of 1 to 2 percent for positive drainage, so water sheds to the drains and scuppers instead of pooling. The exact slope is the engineer's and the code's call, so confirm it rather than assuming the deck has it. Where an existing deck ponds because it was built flat or has deflected, the long-term fix is to correct the slope or add drains, not to trust a coating to live underwater. A coating restores the surface, it does not restore the slope, the same point the roof coating guide makes about a ponding roof.

Keep the drains clear, too. A blocked drain turns a sloped deck into a ponding one, and the water goes back on the membrane it was designed to shed.

Wet-film and dry-film: building the mils

The system performs and carries its warranty only at the specified film thickness, measured in mils, thousandths of an inch. A traffic coating is sold and applied by mils, and the mils are the membrane: the waterproofing, the crack-bridging, and the wear reserve all scale with thickness. Go thin to stretch the pail and you get less of all three, plus pinholes where the wet film ran light.

There are two numbers and you have to hold both. Wet-film thickness is what you read with a notched wet-film gauge as you apply, coat by coat, so you catch a thin pass while it is still wet and fixable. Dry-film thickness is what is left after the coating cures and loses its solvent or water, and it is the number the spec and the warranty are written to. You convert between them with the coating's volume solids: a high-solids coating loses less thickness drying than a thinner-bodied one. The data sheet gives the volume solids and the target dry mils, and the coverage rate in square feet per gallon follows from them, the same wet-versus-dry and coverage math worked in the roof coating mil and yield material.

Apply to the spec dry mils for the traffic class, read wet mils on a grid as you go, and confirm the dry film after cure. The thickness is not where the savings are. It is the whole point of the build.

The cure and the recoat window between coats

Each coat has to cure enough to take the next one, and the window when it will is set by the product, the temperature, and the humidity, not by the clock in your head. Recoat too soon and the coat underneath has not developed enough to hold the next, so you trap solvent or uncured material and get a soft film that blisters. Recoat too late and a fully cured urethane can lose its chemical grip on the next coat, so you may be forced to abrade or prime the surface to get the bond back.

This is why the recoat window comes off the data sheet for the exact product and the conditions on the day. A two-component urethane that cures by reaction sets on a fairly predictable schedule that shifts with temperature. A one-component urethane that cures by reacting with atmospheric moisture speeds up in humidity and slows in dry cold, which can stretch the window in ways that surprise crews used to the two-part material. Cold slows every chemistry down.

Plan the coats around the window, not the shift schedule. If the base needs overnight before the broadcast coat at the temperature you have, it needs overnight, and rushing it to keep the crew moving is how you build a delamination between layers that nobody sees until traffic finds it.

Weather, temperature, and the dew point

Weather decides whether the coating cures into a membrane or never gets the chance, so the application window is part of the spec. The coating goes on within the product's temperature range, with the surface and air inside the limits on the data sheet and the relative humidity under the stated cap. Confirm the numbers for the product, because they shift by chemistry.

The dew point is the one crews skip and regret. A common rule across coatings is to keep the substrate at least 5 degrees F above the dew point during application and cure, because a surface at or below the dew point has invisible condensation on it, and the coating then goes down onto a film of water and never bonds. Check the surface temperature and the dew point with a meter, first thing in the morning and again as the deck cools in the evening, not by feel. Rain is the other hard line. A coating washed off before it cures is a full redo, so hold the rain-free window the manufacturer calls for.

One-component urethanes add a twist worth knowing. They are moisture-cure, so they need humidity in the air to cure and can cure too fast in heat or stall in dry cold. The same dew-point and rain discipline the roof coating guide spells out applies here, on a deck that cannot be left half-cured under traffic.

Testing: adhesion, wet-film, and the flood test

Prove the system instead of trusting it, and do it in three places: before, during, and after. Before the field coat, run an adhesion test to confirm the coating actually bonds to the prepared concrete. The pull-off test, with a dolly bonded to a cured patch and pulled with a gauge, is the common method, and the read is simple: a bond that fails in the concrete or at the spec value passes, a coating that peels clean off the slab means the prep or the primer is wrong and you fix it before you coat the whole deck. Run it in several spots, because a deck reads differently in shaded, oily, and chalked areas.

During application, read wet-film thickness on a notched gauge across a grid so the dry mils land where the spec wants them, and watch for holidays, the pinholes and skips a single pass leaves. After cure, confirm the dry film, and where the design calls for it, flood-test the deck or the detail areas: dam the surface, flood it to a set depth for a set time, commonly on the order of a day, and watch for leaks below. Flood-test only where you can drain and dry afterward, because a leak puts water into the structure you are trying to protect.

Tie every reading to a place and a number. The adhesion values, the wet-mil grid, and the flood-test result are what turn the closeout into a signature instead of an argument, and they are the manufacturer's and the engineer's acceptance criteria, so test to their methods.

Curing before traffic

Cure before traffic, or the coating you just built gets damaged before it is ready to take the load. A traffic coating needs time after the final coat to develop its full properties, and driving or parking on it too soon marks it, tracks it, and can shear the uncured film. The open-to-traffic time is on the data sheet and it splits two ways: a shorter time to light foot traffic and a longer one to full vehicular load, both stretching out in cold weather.

Hold the deck closed for the time the manufacturer states, and stage the reopening if the schedule is tight, foot traffic first and vehicles later. The crew that reopens a parking deck on the calendar instead of the cure spends the savings on the repair.

Maintenance and the recoat cycle

A traffic coating is a maintained system, not a one-time install, and the part that wears is meant to. The top coat and the aggregate are the sacrificial wear surface, and the lifecycle plan is to renew them before the wear reaches the base coat and exposes the waterproofing. Catch it early and the recoat is a wash and a fresh top coat. Miss it and traffic grinds through to the base, then into the concrete, and now you are repairing the deck, not recoating it.

Inspect on a cycle and watch the zones that wear first: the drive lanes, the ramps, and the turning areas where the tires work hardest, and the details where movement and ponding concentrate. The tells are the aggregate worn smooth and showing through, the top coat thin or gone, color faded to the layer below, and any blistering that signals moisture working up from underneath. An annual condition review is a common cadence, and on a structure that depends on the coating for corrosion protection it is cheap against what it protects.

Re-up before the base is exposed. The recoat interval depends on the traffic, the system, and the exposure, so it is set by the wear you actually see, not a fixed number of years. The roof coating guide makes the same case for a coated roof: the surface is renewable on a cycle, and the owner who budgets the recoat as a scheduled item keeps the membrane ahead of the failure.

Restoring an existing traffic coating

Restoring an existing traffic coating starts with an honest assessment of what is there, because the recoat only works over a sound, bonded system. Where the old coating is still adhered and intact, the surface is cleaned, abraded or prepped to the manufacturer's requirement, an adhesion test confirms the new coat will bond to the old, and the system is recoated, often a fresh broadcast and top coat. Compatibility matters: the new coating has to bond to the old chemistry, so the assessment includes identifying what is down.

Where the old coating has failed, debonded, blistered, or sits over delaminated concrete, patching over it just buries the problem. The failed material gets removed back to sound concrete or sound coating, the substrate underneath gets assessed, and any concrete deterioration, the delaminations and spalls from corrosion, gets repaired before the new system goes on. Coating over delaminated concrete or live corrosion locks the failure in under a fresh membrane, and it surfaces again fast.

The line between recoat and remove-and-replace is the assessment, and on a structural deck it belongs to the engineer and the manufacturer, not to a quick look. Sound the deck for delamination, check the bond, identify the existing system, and let the condition set the scope.

What to document

The coating covers the deck and the deck covers the structure, so the record is the proof of what protects the building. When a leak or a spall shows up later, the documentation is what tells you whether the system was right and where to look, and it is what a warranty claim is decided on.

Capture it by area, because one deck rarely gets one build. Record the substrate and its prep, the CSP achieved, the moisture test method and result, the primer, the coating system and chemistry, the target and measured wet and dry mils by coat, the aggregate and broadcast rate, the crack and joint details, the adhesion and flood-test results, the weather at application, and the manufacturer's warranty. Carrying the prep, the mils, and the test results in one field record, the kind of estimate-to-closeout file a tool like FieldOS is built to hold, is what makes the closeout a signature and the warranty defensible.

Common mistakes

• Coating over a wet, green, or uncured slab, so vapor drive blisters and delaminates the membrane.
• Skipping or shortcutting surface prep, so the coating bonds to laitance, curing compound, or dirt and peels.
• Leaving cracks untreated and trusting the field coat to bridge them, so the membrane splits over the moving crack.
• Running the traffic coating across a moving expansion joint instead of terminating into a joint system.
• Building below the specified mils to stretch material, so the membrane is thin, pinholed, and short on wear.
• Coating a deck that ponds, with no slope to drain, so water stands on the membrane around the clock.
• Opening the deck to traffic before the coating has reached its full open-to-traffic cure time.
• Throwing aggregate onto a coat that has already skinned, so the sand sweeps away and the surface polishes slick.
• Skipping the adhesion test, then finding the whole deck did not bond after it is all coated.

Field checklist

Standards and references

The controlling document on a traffic deck is the coating manufacturer's published system and warranty. It sets the approved substrates, the prep and primer, the target dry mils by traffic class, the aggregate and broadcast, the detail and joint treatments, the application conditions, and who may apply it, and the closeout runs against it. Everything else is the framework around that document, so confirm the specifics against the actual product.

ASTM C957 is the material specification for this membrane family, the high-solids, cold liquid-applied elastomeric waterproofing membrane with an integral wearing surface, for decks not under hydrostatic pressure and rated for pedestrian and vehicular traffic. Surface profile comes from the International Concrete Repair Institute, whose CSP scale and Guideline 310.2 define the texture the prep has to reach. Concrete moisture is tested to ASTM methods, the in-situ relative humidity probe F2170, the calcium chloride F1869, and the plastic-sheet D4263, with the pass-fail limit set by the coating manufacturer. Adhesion is confirmed by pull-off testing to the applicable method and acceptance value. Confirm every designation and edition before citing it, because they are revised across cycles.

Two parties govern above the rule of thumb. The structural or waterproofing engineer owns the deck: the slope, the joints, the crack assessment, the corrosion repair, and whether a deck is a recoat or a tear-off. The manufacturer owns the product: the prep, the moisture limit, the mils, and the warranty. The coating is corrosion protection for the structure, so keep the chlorides out of the deck, prepare and dry the slab or it delaminates, detail the cracks, coves, drains, and joints, and build the specified mils. When a rule of thumb meets the engineer, the manufacturer, ASTM, or ICRI, the rule of thumb loses.

Units and terms

A traffic deck job reads across a data sheet, a spec, and an engineer's drawing, and the same idea shows up under different names, so a short glossary keeps the crew, the inspector, and the engineer talking about the same thing.

Thickness is in mils, one mil being one thousandth of an inch, about 25.4 microns, and it is quoted wet or dry, usually exclusive of the aggregate. Coverage is in square feet per gallon. Surface profile is the ICRI CSP number. The terms below are the ones specific to a traffic coating.

Traffic coating

An elastomeric waterproofing membrane on a concrete deck with an integral aggregate wearing surface for foot or vehicle traffic

Elastomeric / urethane membrane

A flexible, usually polyurethane, liquid-applied coating that cures to a continuous waterproof film with enough elongation to bridge cracks

Crack-bridging base coat

The base coat that provides the primary waterproofing and stretches over moving cracks without tearing

Aggregate broadcast

Silica sand seeded into a wet coat for slip resistance and to take the wear of traffic

Vehicular vs pedestrian system

Vehicular systems are built thicker with more aggregate for tires; pedestrian systems are lighter for foot traffic

Surface profile (CSP)

The ICRI concrete surface profile, 1 smooth to 9 very rough, the texture the prep must reach for bond

Wet-film / dry-film mils

Wet film is thickness as applied; dry film is what remains after cure, the number the spec is written to

Cove / detail

The membrane turned up at a wall or curb over a fillet, plus the reinforced treatment at drains, penetrations, and terminations

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