SC Cutback Bitumen: Slow-Curing Grades, Road Oils and What Replaced Them

The governing document is ASTM D2026, Standard Specification for Cutback Asphalt (Slow-Curing Type), with AASHTO M141 as the long-standing equivalent. Read the AASHTO title before anything else, because it states plainly something the ASTM title conceals: Slow-Curing Liquid Asphaltic Road Materials. There is no word cutback in it, and that is not an editorial accident. An SC material does not have to have been cut back at all.

Two production routes, and only one of them is a cutback

A slow-curing liquid asphalt can reach the specification by either of two quite different routes, and the standard accepts both.

• As a residual. Distillation of a suitable crude is stopped short of the point at which a paving-grade bitumen would be produced, and what is drawn off is already a liquid asphaltic material of the right consistency. Nothing has been added and nothing has been thinned. The diluent is simply the heavy oil fraction that was never removed.
• By blending, or fluxing. A harder base bitumen is softened with a heavy, low-volatility petroleum distillate until the blend falls inside one of the four viscosity bands. This is the route that genuinely is a cutback in the ordinary sense, and it is the route by which most SC material offered for export today is made.

The two routes can produce material that meets the same specification lines and behaves broadly the same way on the road, which is why the standard does not care which was used. They matter to a buyer for a different reason: a residual product’s properties follow the crude it came from, while a fluxed product’s properties follow a blending recipe. Where the specification is tight and the tonnage is large, ask which route the offer represents, because it tells you how much batch-to-batch movement to expect.

The diluent is the whole story

Every difference between the three cutback families comes from one decision: what the bitumen was thinned with. RC grades under ASTM D2028 use a gasoline or naphtha-range solvent that boils away in hours. MC grades under ASTM D2027 use a kerosene-range distillate that leaves over days — the mechanism is set out in detail on the MC-70 page. SC grades use a heavy, low-volatility oil in the gas oil range, and at any temperature a road ever sees, that oil is not going anywhere in a hurry. The next section deals with what actually happens instead, because it is the single most important thing to understand about this family and it is routinely described incorrectly, including by people selling it.

How the grade names are built

The naming logic is the same arithmetic used across the whole cutback system, and it is worth restating because it is the half of the designation that buyers misread. The number is the lower bound of the kinematic viscosity band at 60 °C in centistokes, measured by ASTM D2170, and the upper bound of every band is exactly twice the lower one:

• SC-70 — 70 to 140 cSt at 60 °C. The most fluid grade in the family, and the only one that will spray without substantial heat.
• SC-250 — 250 to 500 cSt. The general-purpose road oil of the series.
• SC-800 — 800 to 1600 cSt. Heavy enough that it must be worked hot and will not be applied cold under any circumstances.
• SC-3000 — 3000 to 6000 cSt. The stiffest grade in the family and the closest of the four to a paving binder in consistency.

Two observations follow directly. First, there is no SC-30. The 30-grade exists only in the medium-curing series, where MC-30 is the fluid prime coat material; the SC family starts at 70 because a slow-curing product of MC-30 consistency has no job that a lighter material does not do better. Second, the numbers repeat across families and mean nothing about cure. SC-70, MC-70 and RC-70 share one viscosity band and nothing else — different standards, different diluents, different flash point methods, different cure mechanisms and different applications. Ordering a cutback on the number alone is the most common and the most consequential mistake in this product family, and the grade-naming logic behind it is covered further on the bitumen grades page.

Why this page covers the family rather than the grade

Individual SC grades are rarely bought by name today. Where a slow-curing material is still specified, the enquiry usually arrives as road oil, as slow-curing cutback, or as a line copied out of an old national specification, and the grade is settled afterwards from the application temperature and the equipment available. Four thin pages, one per grade, would repeat the same explanation four times and answer nobody’s actual question. The question a buyer arrives with is not what is the viscosity band of SC-800; it is is a slow-curing material the right thing for this job, am I allowed to use it, and if not, what is. That is what this page is written to answer.

Where the name road oil comes from

Before hot-mix plants were common, before emulsion was industrialised, and before anybody measured volatile organic emissions, the simplest way to keep dust down and hold an unpaved surface together was to spray a heavy petroleum oil onto it. The oil bound the fines, waterproofed the surface for a season, and was reapplied when it wore off. When those materials were eventually brought under specification, they became the slow-curing series — which is why the AASHTO document calls them road materials rather than cutbacks, and why the trade name road oil is still the phrase most enquiries use. It is a fair description. An SC grade is much closer to a heavy oil that happens to contain asphalt than to a paving binder that happens to be liquid.

What SC is not

• Not a prime coat grade in modern practice. Priming is MC territory, and increasingly emulsion territory. Some older specifications permitted a slow-curing material on very absorbent bases, but the cure time makes it unworkable on any programme with a surfacing crew waiting. See prime coat vs tack coat.
• Not a tack coat material. A bond coat has to set quickly and stay at the surface. An SC grade does neither and will track under traffic for weeks.
• Not a structural pavement binder. The residue never reaches the stiffness of the base bitumen it was made from, because a substantial part of the oil stays in it permanently.
• Not a recycling or rejuvenating agent. The family of heavy petroleum oils used to restore aged binder in hot-mix recycling is classified separately under ASTM D4552, and those products are specified against different criteria. An SC grade is not a recycling agent and must not be substituted for one because the viscosity looks similar.
• Not a fuel oil, and not waste oil. Spraying used engine oil or unspecified waste hydrocarbon on a road is the practice that got petroleum dust palliatives regulated in the first place, and it is not what ASTM D2026 describes.

What an RC or MC grade does

A rapid or medium-curing cutback is a delivery system. Paving bitumen is thinned with a solvent light enough to boil away at ambient or near-ambient conditions, sprayed while it is fluid, and then abandoned by its solvent. The solvent evaporates, the binder left behind — the residue — stiffens back towards a working paving consistency, and the pavement ends up with something close to the material the refinery started with. The specification reflects that: ASTM D2027 requires a minimum distillation residue of 50 vol % for MC-30 and 55 vol % for MC-70, so up to half the volume in the drum is solvent that is expected to leave.

What an SC grade does instead

Now read the distillate column in the table above. SC-70, the most fluid grade in the slow-curing family, yields between 10 and 30 % distillate when driven all the way to 360 °C. SC-3000 may yield nothing. A road surface in a hot climate might reach 70 °C on a bad afternoon. The oil in an SC grade is not volatile at any temperature the material will ever experience in service, and the specification says so in numbers.

So evaporation is not the mechanism. Three slower processes happen instead, and they run in parallel over weeks and months rather than hours:

• The lightest tail of the oil does leave. Every distillate is a range rather than a single compound, and the very lightest end of an SC oil is volatile enough to escape slowly at pavement temperatures. That is the 10 to 30 % that SC-70 can give up. It is the smallest of the three effects and the only one that resembles what an MC grade does.
• The oil is absorbed. This is the dominant effect. Sprayed onto a granular base, a soil or an aggregate, the low-viscosity oil phase migrates away from the binder and into the material underneath and around it. It has not left the pavement; it has moved sideways. The binder film that remains is stiffer than the material that was sprayed, because the thing that was softening it has soaked away.
• What remains oxidises. Air and sunlight harden the residual film over months and years, exactly as they harden any bitumen film, and this slowly continues after the first two effects have run out.

The consequence: some of the oil never leaves at all

Absorption relocates the oil; it does not remove it. Beyond that, a fraction of the diluent remains dissolved in the binder film itself and stays there. The residue on the road is therefore permanently plasticised — softer than the base bitumen it was blended from, and softer than it would be if the same job had been done with a hot binder or an emulsion. It never fully hardens because there is nothing left to drive out.

Four practical consequences follow, and every one of them is a reason SC belongs to the jobs it belongs to:

• It is not a structural binder. A bound layer carrying wheel loads needs a binder that develops and keeps a defined stiffness. An SC residue does not. It binds fines, it waterproofs and it holds a surface together, and that is the ceiling of what it does.
• It stays temperature-susceptible. A permanently softened binder softens further in summer heat. SC-treated surfaces bleed and pick up under traffic in hot weather far more readily than a properly cured MC prime or an emulsion seal, which is a large part of why the material was confined to low-traffic work.
• It stays vulnerable to water for longer. A soft, oil-rich film is more easily displaced from a mineral surface by water than a fully cured one, so the adhesion question — covered on the adhesion and anti-stripping page — sits behind every SC application on a wet site.
• The oil is still in the ground. A hydrocarbon that was absorbed into a base, a shoulder or a subgrade is a hydrocarbon left in the environment. This is the argument that eventually closed most markets to the family, and it is dealt with further down.

Why the residue is measured by ASTM D243 rather than by distillation

This is the tidiest evidence that the family works differently, and it is written into the specification. For an MC or RC grade you distil the sample, weigh or measure what is left, and run penetration, ductility and solubility on that residue — the question being how much binder does this drum contain and how hard is it. Try the same thing with an SC-3000 and the test tells you almost nothing, because almost nothing distils.

ASTM D243, Residue of Specified Penetration, asks the question the other way round. The sample is heated and hardened under controlled conditions until the residue reaches a penetration of 100, and the test reports how much material is left at that point, by mass. Instead of measuring how much solvent goes, it measures how much material of a defined consistency you have. The requirement rises across the family — a minimum of 50 wt % for SC-70 up to 80 wt % for SC-3000 — and that ladder is simply the statement that a stiffer grade contains proportionally more useful binder and less oil.

The vocabulary problem

The industry settled on slow curing decades ago and the term is now fixed in every specification, so it has to be used. It should not be believed. What an SC material does is set up: it stiffens over weeks as oil migrates out of the film and the film oxidises, it never reaches the condition of a cured binder, and there is no point at which it can be called finished. Curing times quoted for SC are therefore an estimate of when the surface will take traffic, not a statement that a chemical process has completed. Those estimates belong to the national specification and the site trial, not to the product standard, which sets no cure time for any grade.

What this means for anyone who has already bought some

If a slow-curing material has been applied and the surface is still soft after the period the specification allowed, the diagnosis is rarely it needs more time. It is more often that the surface was too tight to absorb the oil, that the weather has kept it cool, that the rate was too high, or that the material was the wrong choice for the job. Adding heat, sanding the surface and waiting are the three field responses, and only the third of them works on the underlying mechanism. A blotter of clean sand or fine chippings will let a surface carry traffic while it continues to stiffen — that is common practice and it is worth planning for from the start rather than improvising it.

Why the number is higher

Flash point is the temperature at which a liquid gives off enough vapour to form an ignitable mixture with the air above it, and for a cutback it is set by the diluent rather than by the bitumen. An RC grade carries a naphtha-range solvent and flashes accordingly. An MC grade carries kerosene and flashes at a minimum of 38 °C for the two lightest grades. An SC grade carries a heavy oil that produces very little vapour at ordinary temperatures, and the specification minimum rises with it.

Notice how the requirement is laddered across the family: 66, 79, 93 and 107 °C for SC-70, SC-250, SC-800 and SC-3000 respectively. That is not a coincidence and it is not generosity. Each stiffer grade has to be heated further before it will spray or mix, so the specification raises the flash point requirement in step with the working temperature the grade will demand. The margin does not necessarily grow as you go up the series — the requirement moves because the operating temperature moves.

The method is not interchangeable, and neither is the value

ASTM D2026 sends the flash point test to ASTM D92, Cleveland open cup. ASTM D2027 and ASTM D2028 send RC and MC to the Tag open cup — ASTM D1310, with ASTM D3143 as the cutback-specific Tag open cup procedure, the apparatus written for liquids that flash at or near ambient temperature. These are different pieces of apparatus operated in different ways, and a value from one is not a value from the other. Three practical rules follow:

• Do not compare an SC Cleveland figure against an MC Tag figure and conclude anything about relative hazard. They answer the same general question in different equipment.
• Do not accept a Tag open cup result on an SC certificate, or a Cleveland result on an MC certificate. The wrong method on the wrong product is a documentation error at best and a safety-case error at worst, and it is one of the quickest signs that a certificate was assembled rather than measured.
• Neither open cup value is the transport number. Dangerous goods classification is assigned from a closed cup result, normally Pensky-Martens to ASTM D93, and a closed cup always reads lower than an open cup on the same material.

What the higher flash point genuinely buys

One thing, and it is worth having. A drum of MC-70 standing unshaded on a tropical quay reaches its own 38 °C flash point on weather alone, with nobody having connected a heater; the vapour space goes flammable by lunchtime. An SC drum does not do that. At 66 °C minimum for the lightest grade and 107 °C for the heaviest, ambient conditions do not put an SC container inside its flammable range. Storage, stacking, port handling and the ordinary life of a drum in a yard are materially less hazardous with an SC grade than with a light MC or any RC grade.

What it does not buy

• SC-70 has very little margin at the spray bar. Work it out from the specification rather than taking it on trust. SC-70 measures 70 to 140 cSt at 60 °C, and spray application wants a much thinner liquid than that if the bar is to lay an even fan. Getting there means warming the material into and past the region of its own 66 °C minimum flash point. SC-70 is therefore in exactly the position the MC grades are in: routinely worked at or above its own flash point, with the tank vapour space to be treated as flammable throughout the shift.
• The heavier grades are worked genuinely hot. SC-3000 at 3000 to 6000 cSt at 60 °C needs substantial heat before it will atomise or coat aggregate. Its 107 °C minimum flash point sounds comfortable until it is set beside the temperature the grade actually has to reach. Never assume the margin is wide; establish it from the batch value and the working temperature you intend to use.
• The specification value is a floor, not a description of your cargo. The 66 °C in ASTM D2026 is the minimum SC-70 must clear. The number that governs your tank is the measured Cleveland open cup value printed on the batch Certificate of Analysis. Chalk it on the tank and set the thermostat from it.
• A fire is still a hydrocarbon fire. A higher flash point means the vapour is harder to ignite. Once a body of hot oil is burning, the fact that it was difficult to light is of no help to anyone.

Heating rules

• Indirect heat only. A hot oil jacket, a steam coil or a hot water bath. Nothing that burns, glows or arcs goes near a vessel containing an SC material — no burner tube under a drum, no torch on a seized closure, no immersion element in a part-empty drum, no improvised heat trace. An SC material must never be heated with an open flame, and drums and tanks must never be stored or stood near an ignition source — a burner, a kettle, a welding or cutting bay, a generator or vehicle exhaust, or an electrical fitting not rated for a flammable atmosphere. The diluent is a petroleum distillate and the liquid is a combustible hydrocarbon regardless of how comfortable the flash point number looks.
• Keep the heating surface covered. Product must cover the coil before heat is applied and stay over it as the tank draws down. An exposed coil firing through a surface film locally overheats the oil, cokes it onto the tube, and puts hot metal into a vapour space.
• Two independent temperature controls. A control thermostat and a high-temperature cut-out on a separate sensor and a separate circuit, both proved before the season. An untested cut-out is a label.
• Heat what you will use. Holding an SC grade hot for days drives off the lightest fraction of the oil, and the viscosity of what remains climbs quietly out of its band with nothing appearing on any delivery note. On a heavy grade held hot, this is the mechanism that turns a sprayable material into one that will not pump.
• Never share a vessel with hot bitumen. The catastrophic flash that follows tipping an MC grade into hot binder is less likely with a heavy oil, but the rule stands: a tank, line, pump or distributor that has carried hot binder is cooled and cleaned before it sees a liquid asphalt, and a vessel that is merely empty still counts as hot. See bitumen storage tanks and the heating temperature guide.
• Do not blend or thin on site. Adding oil to a bitumen tank, or adding hot bitumen to a vessel containing a liquid asphalt, is how people are killed, and a site blend will not meet the specification in any case. Hitting a viscosity band says nothing about the distillate profile or the residue of specified penetration, which are the lines that determine what the road ends up with.

Water: the hazard that gets worse with SC, not better

ASTM D2026 allows up to 0.5 vol % water by ASTM D95, a looser limit than the 0.2 vol % ASTM D2027 applies to the MC grades. That looks like a relaxation. In practice it moves the hazard in the opposite direction, and the reason is the working temperature.

An MC-70 tank is normally operated in a 50 to 80 °C window — a working range taken from typical industry practice, not from ASTM D2027, which sets no application or storage temperature — entirely below the boiling point of water, so free water in a correctly operated tank spoils the work without ever flashing to steam. An SC-800 or SC-3000 tank does not have that protection: in practice those grades are worked at or above 100 °C, a working temperature set by the equipment and the job rather than by ASTM D2026, which specifies none, and water trapped beneath hot binder expands roughly seventeen hundredfold when it turns to steam. The result is a boil-over that ejects hot liquid out of the hatch. On the heavy slow-curing grades, water in the tank is a genuine steam hazard rather than a quality nuisance. Check drums and tank bottoms for standing water before charging, drain and dry transfer lines at the start of the season, keep closures tight, keep drums off wet ground and covered in wet weather, and treat any tank that has taken rain as suspect until it has been drained.

Vapour, confined spaces and personal exposure

• Assume hydrogen sulphide in the ullage. It accumulates in the vapour space of warm bitumen and liquid asphalt tanks even when the product itself carries very little, and at dangerous concentrations it destroys the sense of smell that would otherwise warn you. Nobody gauges, dips or samples over an open hatch on a warm tank without personal monitoring.
• Any SC tank is a confined space carrying a potentially flammable and oxygen-deficient atmosphere until a gas test read by a competent person proves otherwise.
• No hot work on anything that has held an SC material. Welding, cutting, grinding or drilling a drum or tank has killed people who reasoned that an emptied and drained container was safe. Cleaning, gas-freeing, a gas test, then a permit — in that order.
• Bond and earth every transfer, fill from the bottom or through a dip pipe below the surface, and measure continuity rather than eyeballing a clamp.
• Skin and clothing. Repeated contact with a petroleum oil strips the natural oils out of skin and produces dermatitis, and a soaked overall holds it against the body for hours. Nitrile gloves, gauntlet cuffs outside the sleeve, contaminated clothing off rather than worn for the shift. Never wash binder off skin with solvent, diesel or kerosene.
• Burns. Hot binder inflicts a thermal burn and the oil adds a chemical insult. Flood with clean cold water immediately, keep cooling for at least twenty minutes and continue on the way to hospital. Adhered bitumen stays where it is — once cool it acts as a sterile covering, and removing it takes skin with it. That decision belongs to a burns unit, not a first aider.
• Fire media are foam and dry powder rated for flammable liquids, with carbon dioxide acceptable on a small contained fire. A water jet into burning oil drives water beneath the surface where it flashes and throws burning liquid outward. Water fog from a distance, to cool vessels not yet involved, is its only legitimate role.

Dangerous goods: establish it, do not assume it

The UN entry that covers this family is UN 1999, Tars liquid including road oils and cutback bitumens, Class 3 flammable liquid — the entry name itself contains the words road oils. Whether a given SC batch actually falls under it is a measurement, not a deduction from the grade. Transport regulations classify a Class 3 flammable liquid from a closed cup flash point below 60 °C, closed cup reads lower than open cup on the same material, and an SC-70 with a Cleveland open cup result close to the 66 °C minimum does not prove a closed cup result above 60 °C. The heavier grades, with open cup minimums of 93 and 107 °C, are normally well clear. Two rules cover both directions honestly:

• Never assume an SC grade is exempt because the specification flash point looks high. Take the closed cup value from the batch data and the Safety Data Sheet.
• Never assume it is regulated either, and quietly ship it as Class 3 to be safe. A misdeclaration in either direction is a misdeclaration, and where a material sits outside Class 3 it may still attract separate provisions if it is offered or carried at elevated temperature.

Confirm the classification, the packing group where one applies, and the carrier’s and port’s acceptance with your freight forwarder before fixing the shipment. Where drums are used, specify new steel drums with sound closures — a leaking oil drum is a contamination claim and a slip hazard even where it is not a fire risk — and keep the current Safety Data Sheet with the cargo. Further detail sits on the logistics and shipping page.

One: the cure is too slow to schedule around

An MC prime is commonly surfaceable in 24 to 48 hours — a figure from typical field practice, since ASTM D2027 sets no cure period and the binding one is whatever the project specification allows. An SC treatment stiffens over weeks and never finishes. On a modern programme, where a base is compacted on Monday and paved on Wednesday and the surfacing crew stands idle every day it waits, a binder that is still soft a fortnight later cannot be scheduled around. The family survived as long as it did because it was applied to roads that had no programme — a gravel road treated in spring and left alone until the following year does not care how long the oil takes to set up. Where that is still the situation, the objection does not apply. Where a contractor has to hand a surface over, it is fatal.

Two: the solvent stays in the pavement

This is the engineering objection, and it is the one that cannot be designed around. As set out above, most of the oil in an SC material is absorbed rather than evaporated, and a fraction of it remains dissolved in the binder film permanently. Three things follow.

• The binder never develops its potential stiffness. A layer bound with an SC material has a permanently plasticised binder, so it cannot be given structural credit in a pavement design. Everything it does is surface protection.
• Temperature susceptibility persists. The residue softens again every summer, so bleeding, pick-up and rutting under even light traffic remain live risks for the life of the treatment rather than only during a cure period.
• The oil is left in the ground. A treatment that works by soaking hydrocarbon into a base, a shoulder or a subgrade puts that hydrocarbon somewhere it stays. On a rural gravel road in 1955 nobody was measuring it. Today it is a question about runoff, about groundwater and about what is left behind when the road is rebuilt, and it is asked at permitting stage.

Three: environmental regulation, from two directions

Cutbacks generally came under pressure from the 1970s onwards on air quality grounds. Solvent released from a cutback is a volatile organic compound, volatile organic compounds contribute to ground-level ozone formation, and regulators in North America and Europe responded by recommending or requiring substitution with emulsion, restricting cutback use to defined seasons, or banning the most volatile grades outright. Rapid-curing grades were hit hardest, medium-curing grades were commonly restricted to cooler months or to specific applications, and the pattern spread through national and provincial specifications over the following decades.

The slow-curing family faced a second and different problem. Its volatile emission is comparatively low — that is what the distillate column in the specification table means — so the air quality argument alone was never the strongest case against it. What caught it instead was the regulation of petroleum-based dust suppressants as a category, driven by contamination episodes involving unspecified oils and waste hydrocarbons applied to unpaved roads. Once a jurisdiction begins regulating what may be sprayed on an unsealed surface on soil and water grounds, a properly specified ASTM D2026 material and an unspecified waste oil often end up governed by the same rule, and the honest answer to a buyer is that the distinction has to be argued locally rather than assumed.

A commercial pressure ran alongside both. The diluent in a fluxed SC grade is a usable middle distillate, and permanently surrendering it into a road base became progressively harder to justify when the same material has other uses.

What replaced it: the slow-setting emulsions

Almost every job in the applications list above is now done with a slow-setting bitumen emulsion — CSS-1 or CSS-1h under ASTM D2397 on the cationic side, SS-1 or SS-1h under ASTM D977 on the anionic side. The grade-naming logic is set out on the emulsion grades page. The substitution works because an emulsion delivers the same thing an SC grade delivers — a low-viscosity liquid that penetrates and binds fines — using water as the carrier instead of oil:

• The carrier leaves. Water evaporates and the binder left behind is genuine bitumen at its own consistency, not a permanently plasticised film. The treatment develops real cohesion.
• No solvent, and for unmodified grades no flash point. That removes the air quality objection, most of the fire case, and in most cases the dangerous goods paperwork.
• More binder per delivered tonne than the arithmetic suggests. ASTM D2397 requires a minimum 57 wt % residue for CSS-1 and CSS-1h, and ASTM D977 the same for SS-1 and SS-1h, the residue being measured by distillation to ASTM D6997. Slow-setting grades are commonly diluted 1:1 with clean potable water for dust control and fog seal work — that ratio is established industry practice and neither standard specifies a dilution. Compare offers on residual binder, not on delivered tonnage.
• It handles fines. The cement mixing requirement that defines the slow-setting class — max 2.0 % coagulum, required by ASTM D2397 and ASTM D977 and measured by ASTM D6935 — is a direct proof that the grade survives contact with very fine, high surface area material — which is exactly what a soil stabilisation or dust control job presents.

Where the substitution is not automatic

An honest page has to say where emulsion does not simply win, because a buyer who is told it always does will be caught out by one of these:

• Emulsion must never freeze. The carrier is water; as a practical handling rule the product is at risk below about 4 °C — a figure from industry practice, since neither ASTM D2397 nor ASTM D977 sets a storage temperature — and once frozen the break is permanent and unrecoverable. A remote site with no heated storage and a cold season has a genuine problem that a cutback does not have.
• Emulsion has a shorter practical working life in store, and its properties move measurably while it sits. A material that must be shipped a long way and then held for months before use is a harder case for emulsion — see shelf life and storage.
• Emulsion needs the charge chemistry to be right. Cationic grades bond to siliceous aggregate, anionic grades suit carbonate stone, and a mismatch produces a treatment that never properly breaks. Where the aggregate is unknown, that is a real risk to manage rather than a formality.
• Emulsion needs its own equipment discipline. Cationic grades are acidic and attack aluminium, zinc, galvanised coatings and copper alloys, so the tank, pump, valves and couplings all have to be mild or stainless steel.
• Some markets never had the regulatory pressure. Where slow-curing materials remain permitted and locally produced, they remain in use, and a specification that names them is not necessarily out of date.

The honest summary for a buyer

If you are asking for an SC grade today, two questions come before anything else. Is the material permitted for this work at this destination? A cargo that cannot legally be applied is a total loss, and the rule may sit in air quality legislation, in a dust suppressant regulation, in the project specification, or in all three. And is an emulsion the better answer? For most of the jobs SC used to do, in most places, it now is — and the cases where it is not are specific, identifiable and worth stating in the enquiry so that the offer can be checked against them.