Cutback Bitumen MC-250: Specification, Cold Mix Applications and Safe Handling

Cutback bitumen MC-250 is a medium-curing cutback: a paving-grade bitumen let down with a kerosene-range petroleum distillate until it is a pourable, sprayable liquid at temperatures far below those of hot mix. Once it is on the road or on the stone the diluent walks out of the film over the following days, and what stays behind — the residue — stiffens back towards a paving consistency. The residue is the only part of the delivery that carries load. The grade is specified in ASTM D2027, with AASHTO M82 as the identical highway-agency version. Read a cutback certificate with that division in mind: one line describes the liquid you unload, and almost every other line describes the binder the pavement actually keeps.

Two symbols, two independent facts. MC fixes the diluent family — a kerosene cut — and with it the cure rate, which for the medium-curing series is counted in days: much slower than the hours of a naphtha-cut RC grade under ASTM D2028, much faster than the weeks or months of a gas-oil-cut SC grade under ASTM D2026. 250 fixes the consistency. It is the floor of the kinematic viscosity band at 60 °C in centistokes to ASTM D2170, and because every band in the ASTM cutback system closes at exactly twice its floor, a conforming MC-250 measures between 250 and 500 cSt. Neither symbol tells you anything about the hardness of the bitumen underneath. The structure of all three curing series is tabulated on the cutback bitumen hub page.

Where MC-250 sits in the MC series

Five grades make up the medium-curing series and the viscosity floor roughly triples at each step. MC-250 is the third of them, and the hinge on which the series turns:

• MC-30 — 30 to 60 cSt. The most fluid cutback in the standard. Priming grade for tight, fine-graded, heavily compacted bases.
• MC-70 — 70 to 140 cSt. Priming grade for open and coarse-textured bases, and the lightest grade that will hold together as a short-life cold mix.
• MC-250 — 250 to 500 cSt. About three and a half times the viscosity of MC-70 taken grade for grade. Surface dressing, patch mixing, stockpile cold mix and road mix.
• MC-800 — 800 to 1,600 cSt. The same list of jobs, with a stiffer residual film, a longer stockpile life and roughly twenty degrees more heat needed to spray or coat.
• MC-3000 — 3,000 to 6,000 cSt. The stiffest grade in the standard, for road mix and plant mix with coarse aggregate, and rarely moved as an export cargo.

The grade where the series changes job

A prime coat has to travel into a compacted granular base — commonly a few millimetres of visible penetration — to bind the surface fines and leave a film the surfacing can key into. That movement is capillary flow, and viscosity is the resistance term in it. MC-250 is about three and a half times as viscous as MC-70 taken grade for grade, and roughly eight times as viscous as MC-30. At that consistency the binder does not enter a compacted base within any useful working period. Sprayed on one it bridges the surface voids, sits on top, and cures into a skin that traffic lifts off in sheets and that becomes a slip plane under an asphalt layer.

So the whole logic of the grade changes at this rung of the ladder. MC-30 and MC-70 are chosen because the binder has to move after it lands. MC-250 is chosen because the binder has to stay where it lands — held on the surface under a chipping cover in a surface dressing, or held as an individual film on each stone in a mix. Everything else on this page follows from that one distinction.

The legacy Saybolt designation

Before kinematic viscosity became the classifying property, cutbacks were graded on Saybolt Furol viscosity and numbered MC-0 through MC-5. The grade customarily cross-referenced to today’s MC-250 is MC-2. Treat that as a trade convention rather than an equivalence written into ASTM D2027: where a bill of quantities, a project document or an older national specification still calls for MC-2, quote MC-250 against it explicitly and obtain the engineer’s written acceptance of the substitution before the cargo is fixed.

What MC-250 is not

• Not a prime coat material. This is the most common ordering error on the grade, and it usually arises when MC-250 is offered as a substitute because the priming grade is short. What you get is a skin sitting on an unbound base, not a prime.
• Not a tack coat. A bond coat between pavement layers has to break or set quickly and must not track under construction traffic. Modern practice puts that work on emulsions.
• Not interchangeable with RC-250 or SC-250. The viscosity band of 250 to 500 cSt is the only thing the three have in common. Diluent, cure speed, flash point, application and governing standard all differ, so a purchase order that names the number without the letters is not a specification.
• Not a hot binder. None of the habits that are safe with penetration grade bitumen at 160 °C carry across to a liquid that gives off ignitable vapour at 66 °C and is worked at 75 to 105 °C.

Take the MC series as a ladder and climb it one rung at a time. Each step changes one thing directly and three things as a consequence.

Step one: the number is a viscosity, and the viscosity is set by dilution

The same base bitumen can be turned into any MC grade. What changes between them is how much diluent goes into the blend. More kerosene gives a thinner liquid and a lower grade number; less kerosene gives a stiffer liquid and a higher grade number. The kinematic viscosity at 60 °C measured under ASTM D2170 is simply the way that dilution is expressed and controlled. MC-250 is stiff because it is less dilute, not because it is made from a harder bitumen — the residue penetration requirement is the same 120 to 250 dmm across every MC grade.

Step two: less diluent means more residue per litre

The consequence shows up in the ASTM D402 distillation, which is the line on the specification that tells you what you are really buying. The minimum residue from distillation to 360 °C rises steadily up the ladder: 50 % by volume for MC-30, 55 % for MC-70, 67 % for MC-250, 75 % for MC-800 and 80 % for MC-3000. Subtract those from 100 and you have the maximum diluent the grade may contain. MC-250 is therefore at most about a third solvent, against about half for MC-30.

This is the commercial half of the story and it is where money is won and lost. Freight, drums, handling and duty are all paid on the whole liquid, but the pavement only keeps the residue. A tonne of MC-250 delivers materially more binder to the road than a tonne of MC-70, and any comparison of cutback offers made on price per tonne of liquid rather than price per tonne of residual binder is comparing the wrong thing.

Step three: the diluent is not only smaller, it is heavier

ASTM D2027 does not stop at the residue figure. It also limits how much distillate is recovered at 225 °C, 260 °C and 316 °C, expressed as a percentage of the total distillate recovered to 360 °C. Those limits tighten as the grade number rises: a higher MC grade is required to give up less of its diluent at the lower temperatures. In other words the kerosene cut used in MC-250 is drawn from a heavier, less volatile part of the distillate range than the cut used in MC-30. The solvent charge is smaller and slower.

These are the specification lines that separate a properly blended MC-250 from a stiff cutback that has simply been thinned to hit a viscosity number, and they are the lines most often missing from a weak certificate. Ask for them.

Step four: fewer light ends means a higher flash point

The flash point of a cutback is set by its light ends, not by its bitumen. Take the light ends out and the temperature at which the liquid gives off an ignitable vapour rises. That produces the one genuine discontinuity in the MC ladder. MC-30 and MC-70 both carry a Tag open cup minimum of 38 °C. MC-250, MC-800 and MC-3000 all carry a minimum of 66 °C, measured by ASTM D3143. Twenty-eight degrees are gained in a single step between MC-70 and MC-250, and nothing is gained above it.

That step is real and it matters, but it matters in a specific place — see the safety section below. It protects the drum in the container and the drum in the stockyard. It does not protect the tank at working temperature, because the working temperature climbed with it.

Step five: cure is two effects pulling in opposite directions

Here is where most published summaries oversimplify. It is often said that higher MC grades cure faster because they contain less solvent. That is only half true, and the other half is what makes MC-250 useful.

• Less solvent to remove. A litre of MC-250 has to shed only about a third of its volume against about half for MC-30. Fewer litres of diluent per square metre means a shorter road to a cured film.
• Heavier solvent, leaving more slowly. The same litre is holding a less volatile cut, and a less volatile cut takes longer to evaporate at any given temperature and film thickness.

Which effect wins depends entirely on the geometry of the application. In a thin film with a large exposed surface — a sprayed surface dressing under a single layer of chippings, or a patch spread 40 mm deep and kneaded by traffic — the first effect dominates and MC-250 reaches a serviceable condition in days. In a deep, sheltered, low-ventilation mass — a covered stockpile of coated aggregate two metres high — the second effect dominates and the mix stays workable for months. The same property gives opposite outcomes, and the variable is film thickness and air movement, not the grade alone. That is precisely why MC-250 is the stockpile patching grade and MC-70 is not.

Step six: the working temperature climbs with the viscosity

A stiffer liquid needs more heat to atomise through a spray bar or to coat a stone evenly. Typical published spray windows step up the ladder in step with the viscosity bands, from around 30 to 60 °C for MC-30 to around 75 to 105 °C for MC-250. Compare each window with the flash point below it and the safety consequence becomes obvious. MC-30 has a window that straddles its own 38 °C flash point and tops out around 20 °C above it. MC-70 shares that 38 °C flash point and is sprayed up to about 40 °C above it. MC-250 has a flash point 28 degrees higher, and is sprayed up to about 40 °C above that. Climbing the ladder never buys you a working temperature below the flash point. Up to MC-70 both numbers move together; from MC-250 upwards the flash point is pegged at 66 °C while the working temperature keeps climbing, so every grade above MC-250 is sprayed further above its own flash point, not less far.

The one-sentence version

A higher MC number means less solvent and a heavier solvent, which means more binder delivered per litre, a higher flash point in storage, a faster cure in a thin film and a slower one in a stockpile, and a higher temperature needed to spray or mix it. If you can hold those five consequences in mind you can select any grade in the series without a table.

What the 28 degree step actually buys

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. For MC-250 the governing figure is a Tag open cup minimum of 66 °C under ASTM D2027, determined by ASTM D3143 — the Tag open cup method written specifically for cutback asphalt, the general Tag open cup method being ASTM D1310. It is not the Cleveland open cup figure from ASTM D92 that appears on penetration grade and oxidized grade certificates, and the two are not interchangeable. A cutback certificate that reports flash point by D92 has been tested by the wrong method for the product and should be sent back. MC-30 and MC-70 carry a Tag open cup minimum of 38 °C against MC-250’s 66 °C. Put that 66 °C figure against the temperatures a drum genuinely reaches in the export trade:

• A closed steel shipping container standing on a tropical quay routinely exceeds 60 °C internally.
• A dark drum in direct sun in an unshaded compound passes 38 °C on an ordinary summer afternoon and can climb well beyond it.

For MC-30 and MC-70 those conditions put the vapour space at or above the flash point with nothing happening at all — the hazard requires only weather. For MC-250 the same conditions normally leave the vapour space below the flash point. That is what the 28 degree step buys: a genuinely lower risk in the stored drum, the stuffed container and the yard. It is a real and worthwhile advantage and it is the main reason MC-250 is easier to move and store than the lighter grades.

It buys nothing at all at the spray bar. MC-250 is normally applied at 75 to 105 °C, which is above its own flash point across the whole window. Every vessel holding MC-250 at working temperature — the distributor tank, the transfer line, the pugmill, the open drum being decanted — must be treated as containing a flammable atmosphere at all times, exactly as for the lighter grades. The common site rule of holding a tank a fixed number of degrees below the flash point cannot be satisfied while spraying MC-250 properly, and pretending otherwise is how people convince themselves the heavier grade is safe.

Heating: indirect only, and never an open flame

• Every watt of heat must arrive indirectly — through a hot oil jacket, a steam coil or a hot water bath. No direct flame, no burner tube, no torch, no exposed electric element, no ignition source of any kind against the vessel. Drum and kettle heating practices that are routine and acceptable for paving bitumen are lethal applied to a cutback.
• The heating surface must be submerged in product whenever it is live. An exposed coil boils diluent off the film clinging to it and puts hot metal straight into a flammable vapour space; interlock the heater to a low-level switch if the tank has one.
• Fit a working control thermostat and an independent high-temperature cut-out, and verify both before the season starts rather than after the first incident.
• Work to the measured flash point on the batch Certificate of Analysis and to the supplier Safety Data Sheet, not to the 66 °C specification minimum. Write the batch figure on the tank.
• Heat only the quantity needed for the day’s work. Prolonged heating strips light ends off the top of the batch and quietly raises the viscosity of what remains — a load that started inside the 250 to 500 cSt band can drift out of it in a tank that is kept hot for a week.
• Keep tank vents clear and vented to a safe place. A blocked vent on a warming cutback tank is a pressure problem and a fire problem at the same time.

The MC-250 trap: cold drums

MC-250 is stiff at ambient temperature. In cool weather it pours slowly from a drum or not at all, and the standard response on an under-equipped site is improvised heat — a burner beneath the drum, a torch on the chime, an immersion element dropped into a part-empty drum. Each of those puts an ignition source against a container whose vapour space becomes flammable as soon as the contents warm past 66 °C, which is exactly what the heating is intended to achieve. Drum warming for MC-250 must use the same indirect methods as tank heating: a hot water or steam bath, a jacketed cabinet, or a hot air enclosure, applied slowly and uniformly. Never heat a drum that is sealed, and never apply heat to a drum lying in standing water.

Never combine MC-250 with hot bitumen

MC-250 and hot binder must never meet in the same vessel, in either order — not MC-250 poured into hot bitumen, not hot bitumen charged onto MC-250. Paving bitumen is handled at around 150 to 170 °C, roughly a hundred degrees above the point at which the kerosene in MC-250 boils out of solution. The entire diluent charge goes to vapour in seconds, erupting hot material out of the vessel and putting a solvent cloud directly over an ignition source. This exact sequence has caused fatal tank and kettle fires. It also rules out the shortcut version: a distributor, storage tank, transfer line, pugmill or drum heater that has just run hot binder must be cooled and cleaned before MC-250 goes anywhere near it.

The corollary is equally firm: do not make or adjust MC-250 on site. Thinning a stiff load with kerosene to bring it back into band, or blending a heavier grade down to reach MC-250, is how people are killed — and a site blend will not meet the specification in any case, because hitting the viscosity number says nothing about the distillation profile, the residue content or the residue penetration. Cutback blending is a refinery or terminal operation carried out in purpose-built closed equipment with controlled temperature and vapour control.

Water is a bigger hazard at MC-250 temperatures than at MC-30 temperatures

This deserves emphasis because it is a genuine difference between MC-250 and the lighter grades. MC-30 is sprayed at 30 to 60 °C, below the boiling point of water. MC-250 is worked at 75 to 105 °C, at or above it. Any free water in a tank bottom, a transfer line, a drum or a load of aggregate will boil when it meets the binder. A litre of water becomes roughly 1,700 litres of steam, and the result is a boil-over that throws hot flammable liquid out of the vessel. That is why the specification caps water content at 0.2 vol % by ASTM D95, and why the practical rules matter:

• Drain and check tanks, lines and pumps for standing water before the first charge of the season, and dry them.
• Check drums for water in the chime and around the bungs before decanting, and never heat a drum that has water sitting on it.
• Use surface-dry aggregate for mixing. Wet aggregate is both a coating failure and a steam hazard when it meets binder at 90 °C.
• Cover open vessels in wet weather and keep drum bungs tight.

Static, hot work and confined spaces

• Static. Liquid dropped into a tank through air picks up charge, and MC-250 arrives warm into a vessel whose vapour space is already flammable. Load through a bottom-entry connection or a dip pipe that reaches beneath the liquid level, and hold the fill rate down until the inlet is submerged.
• Bonding and earthing. Bond the tank, the distributor, the drum and every piece of transfer equipment to one another and to earth, then test the continuity. A clip fastened to paint, rust or a painted flange is not a bond, and nobody discovers that by looking at it.
• Hot work on emptied containers. A drum or tank that has held MC-250 is more dangerous empty than full, because what remains in it is vapour at an ignitable concentration. No welding, cutting, grinding or other spark-producing work until the vessel has been cleaned, gas-freed and gas-tested, in that order, by someone competent to certify the result. Emptied-container explosions are a recurring cause of death in this trade.
• Low points. Kerosene vapour is heavier than air and settles into pits, sumps, bunds, trenches and tank bottoms, where it can sit undisturbed for hours. Treat the inside of any MC-250 vessel as a confined space that is both flammable and potentially oxygen-deficient, and gas test before anyone enters.
• Hydrogen sulphide. Hydrogen sulphide accumulates in the vapour space of warm cutback and bitumen tanks even where the product itself carries very little, and it deadens the sense of smell before it reaches a dangerous concentration. Do not gauge or sample over an open hatch on a warm tank without personal monitoring and a standby person.

If it catches fire

• Media. Foam or dry powder rated for flammable liquids; carbon dioxide will handle a small contained fire. Site the extinguishers where a fire will actually start — at the distributor, the tank, the mixing plant and the drum decanting point — rather than on a wall in the site office.
• Water. Never play a water jet into burning cutback. The water sinks, flashes to steam beneath the surface and throws burning liquid over a wide radius. Water fog directed from a distance onto the shell of an adjacent tank or drum to keep it cool is a different and legitimate operation; water into the burning liquid itself is not.

Vapour exposure, skin and first aid

• Inhalation. Kerosene vapour brings on headache, dizziness, nausea and central nervous system depression, and the concentrations that do it are reached easily around an enclosed mixing operation, a poorly ventilated tank area or a spray bar worked from downwind. Stand upwind, extract mechanically wherever the work is enclosed, and treat respiratory protection as what you use when ventilation cannot solve the problem, not as a substitute for solving it.
• Burns. An MC-250 burn is worse than an MC-30 burn for a blunt reason: the material is 40 to 50 degrees hotter in normal use and it sticks where it lands. Flood the area with clean cold water at once, keep flooding it for at least 20 minutes, and keep cooling on the way to medical care. Do not peel adhered bitumen off skin and do not dissolve it off with solvent — once cooled it acts as a sterile dressing, and pulling it away takes the skin with it. Removal is a burns unit decision, not a site decision.
• Swallowing. The serious risk is not the bitumen but aspiration of the hydrocarbon fraction into the lungs. Do not induce vomiting. Get medical help immediately and send the Safety Data Sheet with the casualty.
• Skin contact. The diluent strips the natural oils out of skin and causes dermatitis on repeated exposure. Nitrile gloves rather than latex; gauntlet cuffs worn outside the sleeve so that a splash runs off the arm instead of down into the glove; contaminated clothing changed rather than worn out. Never clean binder off skin with solvent, diesel or kerosene.

Dangerous goods classification: do not assume, in either direction

This is where MC-250 differs commercially from its lighter siblings, and it is worth getting right before a booking is fixed. Transport regulations set the Class 3 threshold at a closed-cup flash point of 60 °C or below. ASTM D2027 controls MC-250 by a Tag open cup minimum of 66 °C. Those are two different measurements of two different things, and on the same sample an open cup result normally reads somewhat higher than a closed cup one, because vapour escapes freely from an open dish. A batch sitting near the specification floor can therefore land on either side of the 60 °C closed cup line, and nothing on the specification sheet tells you which side.

• Do not assume it is exempt. A batch sitting at the bottom of the specification can test below 60 °C closed cup and is then a Class 3 flammable liquid in full, normally declared as UN 1999, tars liquid including road oils and cutback bitumens, with the packing group assigned from the measured value.
• Do not assume it is regulated either. Many suppliers and forwarders declare all cutbacks as UN 1999 Class 3 as a conservative default, which is defensible but carries the stowage restrictions, surcharges and paperwork of a dangerous cargo whether or not they are required.
• Settle it from the batch data. The determination is made from the measured closed-cup flash point for the batch and the classification stated on the Safety Data Sheet, confirmed with your freight forwarder for the specific route and destination. Ask for both documents before the shipment is fixed.

Where the cargo is regulated, plan for UN-approved and correctly labelled packaging, a dangerous goods declaration, an IMDG-compliant container packing certificate and a current Safety Data Sheet, and confirm carrier and port acceptance early — some carriers restrict or surcharge Class 3 stowage and routings can differ from those for ordinary bitumen cargo. See bitumen logistics and shipping. Specify new steel drums with sound closures and adequate ullage in every case; a leaking cutback drum is a fire hazard, not a housekeeping problem, and reconditioned drums are the usual source of both leaks and contamination disputes. Store drums upright with bungs tight, under cover, in a cool ventilated place away from ignition sources and well clear of any hot bitumen operation.

The stockpile paradox, and how MC-250 resolves it

A stockpile patching mix has to satisfy two requirements that appear to contradict each other. In the pile it must stay loose and shovel-workable for months, which means the diluent must not leave. In the pothole it must firm up quickly under traffic, which means the diluent must leave. A binder cannot be both volatile and non-volatile, so the contradiction has to be resolved by geometry rather than by chemistry.

It is resolved by film thickness and air movement. Inside a covered pile two metres high, the material is a deep, sheltered mass with very little exposed surface per unit of volume and almost no air exchange. A heavy, low-volatility diluent leaves such a mass extremely slowly. Spread the same material 40 mm deep in a pothole, open it to sun and wind, and knead it under passing wheels, and the exposed surface per unit of volume increases by orders of magnitude. The diluent that took months to move in the pile now leaves in days. MC-250 works as a stockpile binder precisely because its diluent is the heavier, slower cut described earlier — the same property that makes it a poor prime coat makes it a good pile.

Two practical consequences follow. First, keep the pile covered and undisturbed: a pile left open to sun and wind, or turned frequently, will crust on the outside and eventually set through. Second, a patch that is placed and left untrafficked cures far more slowly than one that is trafficked. Compaction and kneading are part of the cure, not just part of the placement.

Draindown: the failure that shows up at the bottom of the pile

If the binder is too fluid for the ambient temperature, it drains off the aggregate under gravity and collects at the base of the stockpile. The top of the pile then becomes dry, dusty and uncoated, the bottom becomes a fat, unusable mass, and the average binder content of the pile means nothing because it is no longer evenly distributed. This is the single most common reason a lighter cutback grade fails as a stockpile binder in a hot climate, and it is the main technical argument for MC-250 over MC-70 and for MC-800 over MC-250 where summer temperatures are extreme. If a trial pile shows binder pooling at the base within days, the grade is too light for the conditions, not the binder content too high.

Aggregate: the half of the mix nobody specifies carefully enough

• Clean. Dust and clay coatings absorb binder and block adhesion between the film and the stone. A mix made with dusty aggregate can look correctly coated on the day and ravel in the first week under traffic.
• Surface dry. Free moisture prevents the binder wetting the stone, and at 65 to 95 °C it also flashes to steam. Cutback mixes are not designed to tolerate wet aggregate the way an emulsion mix is.
• Open-graded and single-size or nearly so. An open grading gives the voids that let the diluent escape once the patch is placed and keeps the mix workable in the pile. A dense grading with a heavy fines content traps solvent and produces a patch that stays soft.
• Compatible with the binder. Acidic and siliceous aggregates such as granite and quartzite can look perfectly coated on the day and then lose the film to water later, because the bond between an acidic stone and a bituminous binder is the weak one. Where stripping is a known local problem the specification will call for an anti-stripping additive and a dosage, and both are outputs of the mix design, not a site decision.

The residual binder arithmetic

This is where cutback quantities are most often got wrong, and the arithmetic itself is trivial once the principle is clear: specifications are written in residual binder, invoices are written in liquid.

MC-250 leaves a minimum of 67 % residue by volume, so one litre sprayed delivers at least 0.67 litres of residual binder. The comparable figures are 0.55 for MC-70 and 0.50 for MC-30. Turn that around to size a purchase. Suppose the surface dressing design in the project specification calls for 1.0 L/m² of residual binder:

Divide the residual rate by the residue fraction and the liquid rate falls out: 1.0 ÷ 0.67 gives about 1.5 L/m² of MC-250. Carried in MC-70 the same 1.0 L/m² of residual binder would take about 1.8 L/m² of liquid (1.0 ÷ 0.55), and in MC-30 a full 2.0 L/m² (1.0 ÷ 0.50). Treat all three as minimum figures: 67 % is a specification floor and the measured residue on a certificate is usually a little above it, which is one more reason to run the sum on the certificate rather than on the standard.

Over 10,000 m² that is roughly 15,000 litres of MC-250 against roughly 18,000 litres of MC-70 to put the same binder on the same road. Add an allowance over the theoretical figure for distributor priming, end-of-run losses and edge overlap. Then convert litres to tonnes using the batch density from the Certificate of Analysis — density is not part of the ASTM specification for cutbacks and varies with the base binder and the diluent fraction, so it cannot be assumed. The method for that conversion is set out on the tonnage and volume conversions page.

The same logic applies when comparing offers. Freight, drums, handling and duty are paid on the whole liquid, so the correct comparison between two cutback grades, or between a cutback and a bitumen emulsion, is landed cost per tonne of residual binder delivered to the road. On that measure MC-250 is materially more efficient than the lighter MC grades, which is a genuine commercial argument for using it wherever the application allows it.

What the design method has to supply

Nothing on this page substitutes for a surface dressing or mix design. The residual binder rate for a surface dressing depends on the nominal chipping size, the texture and hardness of the existing surface, traffic volume and speed, and the local design method the specification names. The binder content of a stockpile mix depends on the aggregate grading, absorption and specific surface. Both are design outputs. What this page gives you is the conversion between the design output and the quantity of MC-250 you have to buy, which is the part that is normally missing.

What goes wrong, and what it means

• Binder pooled at the base of the stockpile. Draindown. The grade is too light for the ambient temperature, or the binder content is above what the aggregate grading can hold.
• Pile crusted or set solid. The pile has been ventilated, not stored — left open to sun and wind, or turned so often that fresh surface kept being exposed. Look at how the stockpile was kept before concluding that the wrong grade was supplied.
• Patch never firms up. Placed in a deep lift, in a sheltered hole, without compaction, or with a dense-graded aggregate that traps the diluent. Place thin, compact properly and let traffic work it.
• Patch ravels within days. Dusty or wet aggregate at mixing, or binder content too low. The coating was never bonded to the stone.
• Uneven spray fan on a surface dressing. Almost always the binder is too cold to atomise. MC-250 is unforgiving of a distributor that has not been brought properly up to temperature.
• Viscosity above the certificate value on arrival. Diluent has escaped through a loose bung, a damaged drum, storage in full sun or prolonged hot storage. The material has drifted towards MC-800 behaviour and will need more heat than planned.