MC-30 is paving bitumen cut with kerosene until it flows at 30 to 60 centistokes at 60 °C. It is the thinnest grade in the ASTM cutback system and the standard prime coat material for granular base courses.
MC-30 is a medium-curing cutback bitumen, produced by blending a paving-grade bitumen with a kerosene-range petroleum distillate until the mixture reaches a defined fluidity. It is specified in ASTM D2027, and identically in AASHTO M82. It is the first and thinnest grade in that specification.
The designation is read in two halves. MC names the diluent family — medium curing, kerosene — which sets the cure speed, the flash point behaviour and the jobs the material suits. 30 is the lower limit of the kinematic viscosity range at 60 °C, expressed in centistokes (cSt, equivalently mm²/s) and measured by ASTM D2170. In the ASTM cutback system the upper limit of the band is always exactly twice the number, so an MC-30 must fall between 30 and 60 cSt at 60 °C. Nothing in the name tells you the hardness of the base bitumen or how much kerosene is in the drum. Only the distillation test and the tests run on its residue tell you that, which is why between them they occupy most of the specification table below.
Look across the three cutback families and MC-30 stands alone. The rapid-curing series under ASTM D2028 begins at RC-70, and the slow-curing series under ASTM D2026 begins at SC-70. There is no standard RC-30 and no standard SC-30, and that is not an oversight in the standards. A naphtha-cut binder thinned to 30 cSt would carry so much volatile light end that it could not be stored or sprayed safely in a hot climate. A gas-oil-cut binder thinned to the same viscosity would shed its diluent so slowly that it would never build a bound film at all. Kerosene sits between the two: volatile enough to leave in a day or two, heavy enough to stay in the film long enough to do useful work.
MC-30 is therefore the point in the whole bitumen product range where a binder becomes, for practical purposes, a low-viscosity liquid that can be sprayed at close to ambient temperature. That single property is what the grade exists for.
Roughly half of it is solvent. ASTM D2027 requires an MC-30 to leave a minimum of 50 % residue by volume after distillation to 360 °C to ASTM D402. That is the lowest residue requirement of any MC grade: MC-70 requires min 55 %, MC-250 min 67 % and MC-800 min 75 %. Two consequences follow, one commercial and one technical.
The binder that carries load in the finished pavement is the distillation residue, not the liquid you unloaded. ASTM D2027 tests that residue in its own right: penetration at 25 °C between 120 and 250 dmm, ductility at 25 °C of at least 100 cm, and solubility in trichloroethylene of at least 99.0 %. A 120–250 dmm residue is considerably softer than a paving grade such as bitumen 60/70 — partly because a softer base binder is used to make the blend, and partly because a small kerosene fraction never fully leaves the film. That residual softness is a feature in a prime coat. A primed base is supposed to stay slightly tacky so the asphalt layer keys into it, not set bone hard.
Specifications written before the kinematic viscosity system took over classified cutbacks on Saybolt Furol viscosity, in the series MC-0 through MC-5. MC-0 is the old designation corresponding to today's MC-30. If a project document names MC-0, quote MC-30 against it in writing and let the engineer approve the substitution rather than assuming the two are interchangeable. How the three cure families and their grade numbers fit together is covered on the cutback bitumen hub page.
What follows is the specification an MC-30 is normally offered against for export, line by line, with the ASTM method that generates each figure. Read the three distillate lines carefully: they are expressed as a percentage of the total distillate recovered to 360 °C, not as a percentage of the original sample. Only the residue line is stated on the sample, and it is the one that tells you how much binder you bought.
| Property | Test method | Unit | Limit |
|---|---|---|---|
| Kinematic viscosity at 60 °C | ASTM D2170 | cSt (mm²/s) | 30–60 |
| Flash point, Tag open cup | ASTM D3143 / ASTM D1310 | °C | min 38 |
| Water content | ASTM D95 | vol % | max 0.2 |
| Distillate to 225 °C | ASTM D402 | vol % of total distillate to 360 °C | max 25 |
| Distillate to 260 °C | ASTM D402 | vol % of total distillate to 360 °C | 40–70 |
| Distillate to 316 °C | ASTM D402 | vol % of total distillate to 360 °C | 75–93 |
| Residue from distillation to 360 °C | ASTM D402 | vol % of sample | min 50 |
| Penetration of residue at 25 °C, 100 g, 5 s | ASTM D5 on D402 residue | dmm (0.1 mm) | 120–250 |
| Ductility of residue at 25 °C, 5 cm/min | ASTM D113 on D402 residue | cm | min 100 |
| Solubility of residue in trichloroethylene | ASTM D2042 on D402 residue | wt % | min 99.0 |
Ordinary paving bitumen flashes above 250 °C and is worked at 160 °C, with a wide margin between the two. MC-30 can flash at 38 °C — a temperature a steel drum reaches standing in the sun. Everything in this section follows from that one number.
It is the vapour that burns, not the liquid. The flash point is the lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture with the air above it. ASTM D2027 sets a Tag open-cup minimum of 38 °C for MC-30, determined by ASTM D3143, the Tag open-cup method written specifically for cutback asphalt; ASTM D1310 is the equivalent general-purpose Tag open-cup procedure and appears on some refinery data sheets in its place. Now put 38 °C next to the temperatures an MC-30 drum genuinely reaches in the export trade:
So the vapour space above the liquid can sit inside the flammable range while nothing is happening at all. That is the fundamental difference between MC-30 and every hot-applied bitumen product on this site: the hazard does not require a process, only weather.
The 38 °C figure is a specification minimum, not a property of your cargo. The limit that governs your storage and your heating is the measured flash point printed on the batch Certificate of Analysis, and that is the only figure worth writing on the side of the tank.
MC-30 is the one cutback that barely needs heating. In a warm climate it sprays at or a little above ambient, and the working window normally quoted for it — roughly 30 to 60 °C — straddles its own specification minimum flash point of 38 °C. That has to be said plainly, because it is the fact most often skated over: towards the top of its ordinary spray window, MC-30 is being handled at a temperature at which it is entitled to be giving off ignitable vapour. The familiar site rule of thumb — hold the tank at least 25 °C below the flash point — simply cannot be satisfied for this grade, and repeating it here would be worse than useless, because it would suggest a margin that does not exist. What replaces it is a different discipline: the drum, the tank and the distributor are treated as containing a flammable atmosphere at all times, whether or not anyone has applied heat.
Precisely because so little heat is required, sites improvise — a burner under a drum, a torch on a cold transfer line, an immersion element in a part-empty tank. Those improvisations are how cutback fires start.
Tip a cutback into hot paving bitumen, or run hot bitumen into a distributor, kettle or tank with cutback still lying in the bottom of it, and the entire solvent charge goes to vapour in a few seconds. The vessel throws its contents out and a vapour cloud forms directly over whatever started the sequence. Tank and kettle fires from exactly this cause have killed people. The prohibition covers the equipment as much as the product: a distributor, transfer line, pump or drum heater that has just carried hot binder is not fit to receive MC-30 until it has cooled and been cleaned out. Blending is likewise not a site activity — it belongs to a refinery or terminal, in closed purpose-built plant with vapour control — so nobody on a road contract should be thinning a stiff load by pouring kerosene into a bitumen tank.
MC-30 releases more solvent into the air per square metre sprayed than any other MC grade, for the simple reason that it contains more of it. Exposure control on a priming operation is a genuine requirement here rather than a formality carried over from a generic method statement.
This is where MC-30 parts company commercially with every penetration-grade product on this site. It moves as dangerous goods, and the usual declaration is UN 1999, tars liquid including road oils and cutback bitumens, Class 3 flammable liquid. One point regularly catches out buyers who read only the product specification: transport classification is decided on a closed-cup flash point, whereas the 38 °C in ASTM D2027 is an open-cup value. A closed cup normally reads several degrees lower than an open cup on the same liquid, so the number that fixes the packing group is not the number printed on the specification sheet. In ordinary practice an MC-30 lands in packing group III, but that is a determination made from the batch data and the Safety Data Sheet by whoever signs the declaration — it is never an assumption carried across from a previous shipment. Work through the consequences before the booking is fixed:
For MC-30 the Certificate of Analysis carries safety information, not only quality information. Four lines matter most: the measured flash point, which sets your temperature limits; the kinematic viscosity at 60 °C, which confirms you received the grade you ordered rather than a stiffer one; the water content, which predicts foaming and eruption on warming; and the residue from distillation, which tells you how much binder you actually bought. A certificate that reports the specification limits back to you instead of measured batch values is not a Certificate of Analysis.
MC-30 is sprayed warm rather than hot, and in many climates it is barely warmed at all. The figures below are the typical operating windows; the flash point on the batch Certificate of Analysis always overrides them.
| Operation | Typical figure for MC-30 | Why it matters |
|---|---|---|
| Spray application temperature | 30–60 °C, and near ambient in warm weather | The most fluid cutback in the system. Note that the upper end of this window lies above the 38 °C specification minimum flash point; heating beyond what the spray actually needs gains nothing and drives kerosene off the top of the tank |
| Maximum tank temperature | Below the measured batch flash point, and as low as the spray will allow | The 38 °C specification floor is not your cargo's flash point — the Certificate of Analysis figure is. Where the spray window reaches or passes that figure, the tank vapour space is flammable and must be managed as such |
| Heating method | Indirect only — hot oil jacket, steam coil or hot water bath | A direct flame, burner tube or exposed element against a Class 3 flammable liquid is how tank and kettle fires start |
| Drum storage | Upright, bungs tight, shaded and ventilated | A closed container in the tropics exceeds 60 °C. Shade and ventilation are the difference between a stored drum and a pressurised one |
| Base surface condition at spraying | Dry to slightly damp, no free or ponded water | Free water blocks capillary penetration and the prime sits on the surface instead of entering the base |
| Base surface temperature | Commonly specified as min 10–15 °C and rising | Below that the binder stiffens on contact and will not travel into the base within the working period |
| Cure before surfacing | 24–48 hours, longer in cool or humid weather | Surfacing over an uncured prime traps kerosene beneath the asphalt and can create a slip plane between the layers |
| Traffic during cure | Keep off; blot with clean dry sand if unavoidable | Uncured prime picks up on tyres in sheets and strips binder out of the top of the base |
Both grades are kerosene cutbacks made to the same standard and both are sold as prime coat material. The choice between them is decided by the texture of the base, and getting it wrong wastes either the binder or the day.
A prime coat is not a bond coat sitting on a surface. It is supposed to enter the base. Sprayed onto a compacted granular base course it should soak several millimetres in, bind the surface fines so they cannot ravel or blow away, waterproof the top of the base against rain before the asphalt goes on, and leave a slightly tacky film that the surfacing keys into. Every one of those functions depends on penetration. A prime that stays on top has failed even if it looks perfect on the day it was sprayed.
Penetration of a liquid into a compacted granular base is capillary flow. The driving force comes from surface tension and from the size of the pores between the aggregate particles. The resistance comes from the viscosity of the liquid. For a given base and a given time, depth of penetration rises as viscosity falls, and it does so roughly with the square root of the ratio — a real effect, but not an unlimited one.
Put the two grades side by side. MC-30 is specified at 30–60 cSt at 60 °C. MC-70 is specified at 70–140 cSt — a factor of about 2.3 stiffer right across the bands. On the square-root relationship that difference alone puts MC-30 roughly one and a half times deeper into the same base in the same time. Treat that as an argument about direction and rough magnitude rather than as a design figure: both bands are defined at 60 °C, and a thin binder film sitting on a base at 25 °C is not at 60 °C, so the viscosity ratio that actually applies on site has to be read from batch data at the working temperature. What does not change is which way the effect runs, and that is why the tightest bases get the thinnest grade.
Two secondary effects push the same way. MC-30 carries more kerosene — minimum 50 % residue against minimum 55 % for MC-70 — so as the surface of the film begins losing solvent, the material underneath stays mobile for longer. And MC-30 is sprayed cooler, which matters less than it sounds: within seconds of landing, a thin binder film is at the temperature of the base, not the temperature of the distributor tank. Viscosity at the base surface, not tank temperature, is what decides how far the binder travels.
A well-compacted, fine-graded crushed stone base with a high proportion of fines has small pores and an almost closed surface. Spray MC-70 onto it and the binder tends to sit in a film on top. That film cures into a skin; the first vehicle onto the section lifts the skin on its tyres in sheets, and the base underneath is left unbound. The instinctive response — increase the application rate — makes it worse, because the additional binder has nowhere to go and simply ponds, and ponded binder under a new asphalt layer becomes a slip plane. The correct response is to move down a grade, not up a rate.
The relationship reverses on an open base. On a coarse, open-textured granular base with large voids, MC-30 can drain away below the zone that actually needs binding, leaving too little binder near the surface to hold the fines or to key the surfacing. There the stiffer grade is correct: MC-70 stays in the upper few millimetres where the work is. MC-70 also cures faster, because it has less solvent to lose, which can decide a tight programme, and it holds a better spray fan in cool weather. If the base is open, if the weather is cold, or if the schedule cannot absorb a two-day cure, look at MC-70 before defaulting to MC-30.
Spray 100 to 200 m² at the design rate, leave it 24 hours, then cut or dig through and look. You want to see the binder darkening the base to a visible depth — many specifications look for something in the order of 3 to 10 mm — with no free binder standing on the surface and no dry, unbound layer immediately beneath a cured skin. Free binder still visible after 24 hours means the rate is too high or the grade too stiff. No visible penetration at all means the base is too tight, too dusty, too cold or too wet, and no amount of extra binder will fix any of those four.
Per litre, MC-30 and MC-70 sit close together. Per tonne of residual binder delivered to the road, MC-30 is the more expensive of the two, because a larger share of what you paid for, shipped and stored evaporates into the air. That is not an argument against MC-30 — on a tight base it is the only one of the two that works — but it is an argument for selecting on base texture rather than on the unit price of the liquid, and for checking that the quantity take-off was built on the grade you are actually going to spray. See tonnage and volume conversions for turning sprayed litres into invoiced tonnes using the batch density from the Certificate of Analysis.
Priming looks simple and is routinely done badly. These six steps are where the failures actually occur, in the order they occur.
The base course must be compacted to the specified density, shaped to level and tolerance, and formally accepted before any binder is sprayed. At the same time check the Certificate of Analysis for the drums on site: kinematic viscosity within 30–60 cSt, measured flash point, water content within 0.2 vol %, and residue from distillation. A drum that has lost kerosene through a loose bung is no longer an MC-30.
Broom or power-sweep the base to remove loose fines and dust without disturbing the compacted surface. Loose fines absorb binder and then break away, taking the prime with them. Where the specification allows it, a light fog of water immediately ahead of spraying can help penetration into a very tight base — but there must be no free or ponded water on the surface when the binder lands.
Check nozzle size and angle, spray bar height and the resulting fan overlap, then verify actual output against a measured tray or by weighing over a known area. Most rate disputes on site are calibration failures, not binder failures. MC-30 is fluid enough that a badly set bar shows up immediately as streaks and drips rather than an even fan.
Apply 100 to 200 m² at the design rate and leave it for 24 hours before committing to the full job. This is the only reliable way to confirm that the chosen rate and grade suit the base you actually built, as opposed to the base described in the specification.
Apply the accepted rate in a single continuous pass at 30–60 °C, working with the distributor moving at the calibrated speed. Do not chase a thin patch with a second pass over cured material, and do not spray if rain is imminent or the base surface temperature is below the specified minimum.
Allow 24 to 48 hours, longer in cool or humid weather. Keep traffic off. If traffic cannot be excluded, blot the surface with clean dry sand and remove the excess before surfacing. Surface only when the prime has penetrated, the surface is tack-free to the touch and no free binder remains standing.
Prime coat rates for MC-30 typically fall between 0.7 and 1.5 litres per square metre, and where they land inside that range is decided almost entirely by how porous the base is. The coverage columns are straight arithmetic from the rate, which is what a buyer needs to convert a road area into a purchase quantity.
| Base condition | Typical MC-30 rate | Area per 1,000 litres | Area per 200-litre drum | What to watch |
|---|---|---|---|---|
| Tight, fine-graded, heavily compacted crushed base | 0.7–0.9 L/m² | 1,110–1,430 m² | 220–285 m² | Penetration is slow. Do not raise the rate to force it in — the surplus has nowhere to go and will pond |
| Dense-graded granular base of normal texture | 0.9–1.2 L/m² | 830–1,110 m² | 165–220 m² | The usual working band. Confirm penetration depth on the trial section after 24 hours before committing to the job rate |
| Open-textured or coarse granular base | 1.2–1.5 L/m² | 670–830 m² | 130–165 m² | Check MC-70 first. MC-30 can drain below the zone that needs binding and leave the surface unbound |
| Dusty, over-broomed or segregated base surface | Trial section required before any rate is fixed | — | — | Loose fines absorb binder and then debond. Sweep and lightly re-compact the surface rather than adding more binder |
Six symptoms cover almost every MC-30 problem reported from site. In five of the six the binder is not the cause.
The rate is too high for this base, or the base is tighter than the design assumed. Blot with clean dry sand and remove the excess before surfacing — do not simply broom the wet binder off, which drags it into windrows. Reduce the rate on the next run rather than accepting a ponded layer that will act as a slip plane under the asphalt.
Look at the base, not the drum. Over-compaction, a sealed surface of fines, free water, or a base surface below about 10–15 °C will each slow capillary flow to the point where the binder does not enter the base inside the working period. Lightly scarify and re-broom, or move to a penetrating emulsion prime. Increasing the application rate on a base that will not accept binder only creates the previous problem.
The material is uncured, over-applied, or was trafficked or surfaced too early. MC-30 has the most solvent to lose of any MC grade and therefore the longest cure — 24 to 48 hours is a normal expectation and cool or humid weather extends it. Sand blotter plus more cure time is the answer; more binder is not.
Almost always mechanical: blocked or worn nozzles, wrong nozzle angle, wrong bar height for the intended triple overlap, or an uncalibrated travel speed. MC-30 is the most forgiving cutback to atomise, so an uneven fan points at the distributor set-up rather than at the binder viscosity.
Kerosene has escaped — a loose bung, a damaged drum, drums stored in full sun, or prolonged heating in the tank. The material has moved towards MC-70 behaviour and will not penetrate a tight base as intended. Re-test before spraying and adjust the grade decision rather than the rate.
Water in the drum, the line or the tank. A litre of water becomes roughly 1,700 litres of steam, which throws hot flammable liquid out of the vessel. This is why the specification caps water at 0.2 vol % by ASTM D95. Drain and check drums, lines and tank bottoms before charging or applying any heat.
Prime coat, in nearly every case. MC-30 is sprayed onto a compacted granular base course to bind the surface fines, waterproof the top of the base against rain before surfacing, and leave a tacky film that the asphalt layer keys into. It is the lowest-viscosity grade in the cutback system, which is why it is chosen for tight, fine-graded or heavily compacted bases where a stiffer grade would sit on the surface. It is also used at light rates as a penetrating primer and dust binder on shoulders and light-duty surfaces.
It is the lower limit of the kinematic viscosity range at 60 °C in centistokes, measured by ASTM D2170. In the ASTM cutback system the upper limit is always exactly twice the number, so MC-30 must fall between 30 and 60 cSt at 60 °C. The MC prefix means medium curing, which identifies the diluent as a kerosene-range distillate under ASTM D2027. The number says nothing about the hardness of the base bitumen or how much kerosene is in the blend; only the ASTM D402 distillation test and the tests on the residue tell you that.
Typically 0.7 to 1.5 litres per square metre of sprayed material, with the figure inside that range set by how porous the base is. A tight, fine-graded, heavily compacted base takes about 0.7 to 0.9 L/m²; a dense-graded base of normal texture takes about 0.9 to 1.2 L/m²; an open-textured base takes 1.2 to 1.5 L/m², and at that point MC-70 is often the better grade. At 1.0 L/m², 1,000 litres covers 1,000 m² and a 200-litre drum covers 200 m² before allowances. Confirm the rate on a trial section of 100 to 200 m² left for 24 hours before committing to the full job.
Viscosity and solvent content, and therefore penetration. MC-30 is 30–60 cSt at 60 °C and leaves a minimum of 50 % residue by volume; MC-70 is 70–140 cSt and leaves a minimum of 55 %. Because viscosity is the resistance term in capillary flow, the thinner MC-30 travels significantly deeper into a tight base in the same time, which is why it is the grade for fine-graded, well-compacted surfaces. MC-70 is the better choice on open or coarse bases, where MC-30 can drain below the zone that needs binding, and in cool weather or on a tight programme, because it has less solvent to lose and cures faster.
ASTM D2027 sets a Tag open-cup minimum of 38 °C, determined by ASTM D3143, with ASTM D1310 as the equivalent general Tag open-cup method. That is a temperature a steel drum reaches standing in the sun, and the inside of a closed shipping container in the tropics exceeds it comfortably. The honest answer on heating is that MC-30's normal spray window of 30–60 °C straddles that flash point, so the familiar site rule of holding a tank well below the flash point cannot be applied to this grade at all. What you do instead: take the measured flash point from the batch Certificate of Analysis, keep the working temperature below it and as low as the spray will tolerate — in a warm climate that usually means applying no heat whatsoever — and treat the vapour space in the drum, tank and distributor as flammable at all times rather than only when it is hot. Heat by indirect means only, such as a hot oil jacket, steam coil or water bath, with the heating surface always covered by product. Never use a direct flame or an exposed electric element, and never add MC-30 to a vessel containing hot bitumen.
Normally 24 to 48 hours, and longer in cool, humid or still conditions. MC-30 carries more kerosene than any other MC grade, so it has the most solvent to lose and the longest cure of the prime coat grades. Surface only once the prime has visibly penetrated the base, the surface is tack-free to the touch and no free binder is standing. Surfacing over an uncured prime traps solvent beneath the asphalt and can create a slip plane between the layers.
Yes, and it is the paperwork rather than the product that delays these shipments. The declaration is normally UN 1999, tars liquid including road oils and cutback bitumens, Class 3 flammable liquid. Watch one trap: the packing group is decided on a closed-cup flash point, while the 38 °C in ASTM D2027 is an open-cup value, so the classification has to be derived from the batch data and the Safety Data Sheet rather than lifted off the specification sheet. In practice MC-30 usually sits in packing group III. Expect to provide UN-approved drums labelled for Class 3, with sound closures and room for the liquid to expand, together with a dangerous goods declaration, an IMDG container packing certificate and a current Safety Data Sheet. Because Class 3 stowage is restricted or surcharged on some services and refused at some ports, obtain written acceptance of the classification and the routing from your forwarder before you fix the booking, not afterwards.
Often, but not always. Emulsion primes carry no solvent, release no volatile organic compounds and remove the site fire risk almost entirely, and in many jurisdictions cutback is now restricted on air quality grounds so emulsion is the only permitted option. Where MC-30 still has a genuine technical advantage is penetration into a tight, fine-graded, well-compacted base: kerosene reduces viscosity and surface tension more effectively than water does, and a purpose-made penetrating emulsion prime has narrowed that gap without entirely closing it on the tightest bases. MC-30 also stores far better than emulsion on a long, unrefrigerated supply line. Confirm first that cutback is permitted at your destination for the intended application and season.
Tell us the quantity, packing, destination port and Incoterm, and add the base type you are priming and the application rate written into your specification — that lets the offer be sized against the road area you actually have to cover rather than against a round tonnage. Two things are worth settling before anything is fixed: that cutback is permitted at your destination for this application and season, and that your carrier will take UN 1999 Class 3 dangerous goods on the intended routing.