1
Roofing felt saturation
Impregnating the organic or glass-fibre carrier so that the felt itself becomes water-resistant and dimensionally stable before any coating is applied.
Oxidized bitumen 85/25 is an air-blown industrial bitumen with a ring and ball softening point of approximately 85 °C and a needle penetration at 25 °C of approximately 25 dmm.
The designation is a pair of measurements, not a brand or a quality claim. The first number is the ring and ball softening point in °C measured to ASTM D36. The second is the needle penetration at 25 °C in tenths of a millimetre measured to ASTM D5. It is emphatically not a penetration range, and a buyer who reads it as one — as though 85/25 described penetration the way 60/70 does — will misjudge the material completely. Trade practice allows about ±5 either side of each nominal figure, which is what puts a cargo sold as 85/25 at 80 to 90 °C on the ring and ball test and 20 to 30 dmm on the needle. The same convention generates every other member of the oxidized bitumen family — 85/40, 90/15, 95/25, 105/35, 115/15 — which is why the grades can be compared at a glance once you know how to read them.
The product is also called blown bitumen, air-blown asphalt, oxidised bitumen or hard bitumen, and it is often written R 85/25 on Indian and European documentation. It is not a paving binder and it is not a harder version of a paving binder. It is a structurally different material made by a separate process step, and it is sold into a different set of industries.
Air blowing takes a soft base — usually vacuum residue or a soft penetration bitumen — and charges it into a blowing column, where compressed air is bubbled through the hot mass at roughly 240 to 280 °C. A catalyst such as ferric chloride or phosphoric acid is sometimes used to shorten the reaction and to steer the softening point rise relative to the penetration drop.
The oxygen does not simply dissolve into the binder. It strips hydrogen from the lighter maltene molecules, which leaves reactive fragments that condense and polymerise into larger asphaltene structures; the removed hydrogen leaves the column mainly as water vapour. The chemistry is therefore a controlled dehydrogenation and condensation, not an oxygen-addition reaction, and the operator stops the blow when the target softening point and penetration pair is reached. Because the reaction is exothermic and self-accelerating, the finished properties depend heavily on how tightly the blowing temperature and air rate were held — which is why batch-to-batch consistency, evidenced by the Certificate of Analysis, matters more with blown grades than with straight-run grades.
Bitumen is a colloidal system: asphaltene micelles dispersed in an oily maltene phase. Blowing raises the asphaltene fraction and depletes the aromatic oils that keep those micelles apart, so the system moves from a sol structure, in which the asphaltenes float freely, towards a gel structure, in which they form a continuous network. The practical consequence is that the softening point rises far more than the penetration falls.
The comparison that makes this concrete: a straight-run 20/30 paving bitumen has roughly the same penetration as 85/25, but its softening point is only in the high 50s to low 60s °C — EN 12591 puts a 20/30 paving grade at 55 to 63 °C. Blowing has therefore bought roughly 20 to 30 °C of extra heat resistance, about 25 °C comparing mid-band to mid-band, at the same room-temperature consistency. That gap is the entire commercial reason blown grades exist.
85/25 sits at the point where the two competing requirements of a roofing binder balance. A softening point of 80 to 90 °C is comfortably above the 65 to 80 °C surface temperature a dark membrane reaches on a flat roof in a hot climate, so the coating does not flow, sag or bleed. A penetration of 20 to 30 dmm still leaves enough softness for the material to saturate a felt carrier, to bond a lap, and to accommodate normal thermal movement of the deck without shattering.
Push the softening point higher, as in 95/25 or 115/15, and heat resistance improves but the material becomes harder to work and less forgiving in cold weather. Move softer, as in 85/40, and flexibility improves but sag resistance on slopes and vertical upstands is reduced. 85/25 is the compromise that satisfies the widest range of roofing-felt plants and membrane specifications, which is why it is the grade most commonly stocked, blown and shipped.
Each line below pairs a typical export value for 85/25 with the standard that actually produces it, so an offer can be checked line by line against the method rather than accepted on the grade name alone.
| Property | Test method | Unit | Min | Max |
|---|---|---|---|---|
| Softening point, ring & ball | ASTM D36 / EN 1427 / IS 1205 | °C | 80 | 90 |
| Penetration at 25 °C, 100 g, 5 s | ASTM D5 / EN 1426 / IS 1203 | dmm (0.1 mm) | 20 | 30 |
| Loss on heating, 163 °C / 5 h | ASTM D6 / IS 1212 | wt % | — | 1.0 |
| Solubility in trichloroethylene | ASTM D2042 / EN 12592 | wt % | 99.0 | — |
| Flash point, Cleveland open cup | ASTM D92 / EN ISO 2592 | °C | 250 | — |
| Specific gravity at 25 °C | ASTM D70 / EN 15326 | — | 1.00 | 1.05 |
| Penetration index, calculated | Pfeiffer & Van Doormaal, from D5 and D36 | — | +2 | +4 |
A blown-grade specification protects against different failure modes than a paving-grade specification, so the lines that matter are not the same ones.
Ring and ball softening point is the single most important acceptance value for 85/25. Bitumen has no sharp melting point, so this is not one. The number is the temperature at which a disc of material held in a brass ring, loaded with a steel ball and heated in a controlled bath, sags far enough to touch the plate 25 mm below it. Treat it as the best available proxy for the temperature at which a coating stops holding its shape on a roof.
A membrane on a dark flat roof in the Gulf, in South Asia or in equatorial Africa will reach 65 to 80 °C at the surface on a summer afternoon. A binder that arrives at 79 °C softening point instead of the specified 80 to 90 °C band is out of grade, and on a sloped or vertical detail it can be the difference between a coating that stays put and one that creeps down the upstand over a season. If you are buying for a hot climate or for a steep application, it is legitimate to ask for the batch that tests in the upper half of the band and to say so in the enquiry.
Penetration measures consistency at ordinary temperature. At 20 to 30 dmm the material is stiff — roughly a third to half as penetrable as a 60/70 paving grade — but not glassy. This range keeps the binder capable of wetting and saturating a felt carrier at application temperature while retaining some capacity to move with the deck when the roof cools at night. A batch at the very bottom of the band is more heat resistant but less forgiving in cold weather; a batch at the top is more flexible but more prone to flow under load.
Neither number alone describes the material. The penetration index (PI), calculated from softening point and penetration by the Pfeiffer and Van Doormaal relationship, expresses how strongly the consistency changes with temperature. Straight-run paving bitumen sits close to 0. A correctly blown 85/25 calculates out at approximately +3, typically in the +2 to +4 range depending on the actual measured pair.
That positive PI is the property being purchased. A high-PI binder changes consistency slowly across the temperature span it will see in service, so it neither runs at the top of the range nor becomes brittle at the bottom. If a supplier's Certificate of Analysis shows a softening point and penetration pair that calculates to a PI near zero, the material has not been properly blown, whatever the label says. This is a check any buyer can run on the COA in under a minute, and it is worth running.
Buyers moving across from penetration-grade paving bitumen often ask why there is no ductility line, and occasionally insist on adding one. The answer is that ASTM D113 measures a property a blown binder is deliberately not designed to have.
The test pulls a moulded briquette apart at 5 cm per minute at 25 °C and records the length at break. For a paving grade the result carries information: a sol-type binder with a continuous maltene phase and dispersed asphaltenes will draw out beyond 100 cm, and a low result signals that the binder has been over-aged, over-cracked, or blended with something that should not be there. Ductility there is a proxy for cohesion and for the health of the colloidal structure.
Air blowing deliberately changes that structure. Raising the asphaltene content and depleting the aromatic oils converts the binder from a sol to a gel — a continuous, cross-linked asphaltene network rather than a free dispersion. A gel-type binder behaves as a stiff elastic solid at 25 °C rather than as a drawable viscous liquid. An 85/25 sample will typically break after only a few centimetres, sometimes under two. That is a correct result for a correctly made product, and a poorly made batch will give a similarly short, similarly uninformative number. A test that returns the same answer for good and bad material discriminates nothing.
Two further reasons make it unsuitable as a contractual acceptance criterion:
One honest qualification, because buyers do meet ductility limits on blown material and should know why. Some product standards for oxidized roofing asphalt — ASTM D312 among them — do carry a nominal minimum ductility of a few centimetres. That is not a contradiction of the argument above; it is a gross-contamination floor, set low enough that any genuine blown bitumen clears it and only heavily filled or adulterated material fails. It is a screening test, not a performance measure, and it is not a reason to write a demanding ductility figure into a trade contract. If your project is written against D312, buy against D312 and require its full test set on the Certificate of Analysis, ductility line included.
If your specification writer wants a genuine cohesion or low-temperature check, ask for something that maps onto the service condition: penetration measured at 0 °C as well as at 25 °C, which is a direct temperature-susceptibility indicator; the calculated penetration index; or a flow and sag test carried out on the finished membrane at its expected service temperature. Those are checks that can actually fail a bad batch.
Loss on heating at 163 °C for 5 hours, to ASTM D6, caps volatile content at a maximum of about 1.0 % by weight. For a blown grade the line earns its place twice over. A result inside the limit says the blow was finished properly and the light ends were driven off rather than left in; a result above it says either that the batch was cut short or that something lighter has found its way into the tank, whether by accident in a shared line or deliberately to bring the consistency back into band. A high loss on heating on an oxidized grade also predicts fuming and softening point drift when the material is held hot in a kettle, which is a site problem as well as a specification problem.
A minimum of 99.0 % soluble matter confirms the product is genuine bitumen and has not been extended with mineral filler, talc or recovered material. Adulteration is a live risk in the industrial-bitumen trade precisely because a filled product can still hit the softening point target — the filler raises the softening point while destroying adhesion and coating quality. If a Certificate of Analysis for a blown grade omits solubility, treat that as a finding and ask for it before shipment.
Cleveland open cup flash point at a minimum of 250 °C is the hard ceiling on heating. It is the value your insurer, your terminal and your site safety officer will ask for, and it appears on the Safety Data Sheet that many destination customs authorities now request. It also sets the working margin discussed in the handling and safety sections below: kettle and melter temperatures must stay well clear of it, not merely below it.
At 1.00 to 1.05 at 25 °C to ASTM D70, oxidized 85/25 sits in the same density region as ordinary paving grades rather than above or below them; treat the band as a consistency check, not as a way of telling a blown grade from a straight-run one. The figure matters for two commercial reasons: it converts between weight and volume on tank and drum reconciliation, and a result above the band is an indirect signal of mineral filler, which pushes density upward. Read it alongside the solubility result rather than on its own — filler shows up far more clearly in the trichloroethylene test.
85/25 is a trade designation, not a standard. The standard most often written into roofing projects is ASTM D312, which classifies oxidized roofing asphalt into numbered types by softening point and penetration rather than by a slash designation, and this is where a preventable dispute arises.
Type III covers a softening point of roughly 85 to 96 °C with penetration at 25 °C of about 15 to 35 dmm; the type below it stops at about 80 °C. The 85/25 band of 80 to 90 °C therefore straddles a gap between two types. A batch testing 87 °C is comfortably inside Type III. A batch testing 82 °C is fully in grade as 85/25, and complies with neither the type below nor Type III, because it falls in the interval the standard does not cover. Nothing is wrong with that material — it simply cannot be certified to a D312 type.
The practical consequence is direct. If your project or your insurer's specification names an ASTM D312 type, do not order to the 85/25 designation and assume compliance follows. Order against the type, and write the measured softening point floor into the purchase contract — for Type III that means requiring the batch Certificate of Analysis to show a softening point at or above the Type III minimum, not merely within the 85/25 band. If the project does not reference D312 and is written on the trade designation, then the 80 to 90 °C band is the correct acceptance criterion and no type certification is needed. Confirm the type limits against the current edition of D312 before drafting, because the standard is revised periodically and the edition named in the contract is the one that governs.
Every oxidized grade designation follows the same convention: softening point in °C, then penetration at 25 °C in dmm, each with a tolerance of roughly ±5. Reading the family side by side shows exactly what you gain and lose by moving grade.
| Grade | Softening point (ASTM D36) | Penetration at 25 °C (ASTM D5) | Where it is normally specified |
|---|---|---|---|
| 85/25 | 80–90 °C | 20–30 dmm | Roofing felt saturation and coating, waterproofing membranes, general industrial use — the volume grade |
| 85/40 | 80–90 °C | 35–45 dmm | Same heat resistance, noticeably softer; membranes and compounds needing more movement capacity |
| 90/15 | 85–95 °C | 10–20 dmm | Harder and stiffer than 85/25; pipe coating compounds, sound-deadening and insulating compounds |
| 95/25 | 90–100 °C | 20–30 dmm | 85/25 consistency with higher heat resistance; hot-climate roofing, slopes and vertical upstands |
| 105/35 | 100–110 °C | 30–40 dmm | High softening point with retained softness; specialised adhesives and industrial compounds |
| 115/15 | 110–120 °C | 10–20 dmm | The hardest widely traded grade; joint filling, high-temperature service, insulating compounds |
The grade covers the bulk of hot-applied waterproofing and bituminous felt manufacture, plus a long tail of industrial compounds.
Impregnating the organic or glass-fibre carrier so that the felt itself becomes water-resistant and dimensionally stable before any coating is applied.
The coating layer applied over the saturated carrier on both faces, which carries the mineral surfacing and does the actual waterproofing work. This is the largest single use of the grade.
Hot-applied and torch-applied oxidised membranes for flat roofs, terraces, podium decks and wet areas, where high softening point prevents flow under solar heating.
Damp-proof courses, basement tanking, foundation and retaining-wall waterproofing, applied hot directly or as a bonding layer for sheet membranes.
Hot-melt adhesive for bonding membrane laps and insulation boards, plus joint fillers, expansion-joint sealants and tank base mastics.
Feedstock for bituminous paints and primers, anti-corrosion coatings, electrical insulating and cable compounds, and sound-deadening compounds for the automotive sector.
Blown grades are supplied solid and must be melted before use. More 85/25 is spoiled by uncontrolled heating than by anything that happens at the blowing unit, because prolonged high-temperature holding continues the oxidation reaction and pushes the softening point off specification.
Confirm the Certificate of Analysis softening point and penetration against the specification, and calculate the penetration index from the pair. Inspect packaging for water ingress: kraft bags stored on wet ground or drums with standing water in the rim are the usual source of kettle incidents.
Break blocks down to a size the melter can take without splashing, and lower them in rather than dropping them. Any water present flashes to steam on contact with hot bitumen and causes violent foaming and ejection from the kettle. Keep a quarter of the vessel as freeboard, so that a charge which does foam has somewhere to expand other than over the operator.
Bring the charge up gradually to a normal working range of roughly 180 to 200 °C, which leaves 50 to 70 °C of headroom below the 250 °C specified minimum flash point. Treat about 230 °C as an absolute ceiling, and be clear about what that ceiling actually buys: it is only some 20 °C below the specified minimum, so it is a limit for a brief excursion, not a temperature to work at. Most batches flash well above 250 °C, but the margin must be taken against the specification minimum, because that is the only figure the contract entitles you to. Use a calibrated thermometer or thermostat that is actually read, not a burner setting, and never fire against a dry vessel wall or an uncovered heating coil.
Draw and apply the material while it is in the working range. Holding 85/25 at high temperature for hours continues to oxidise it: softening point drifts upward, penetration drops, the material stiffens, and adhesion at laps suffers. Melt the quantity the shift will consume, not the quantity the kettle will hold.
Kill the burner before the vessel runs down, so the last of the charge is not baked onto a hot floor and carbonised. Log the temperatures reached and the batch number applied. Keep the sealed retained sample from the shipment until the installation has been through at least one full summer, since that is when a heat-resistance complaint would surface.
85/25 carries no solvent, so none of the vapour precautions that govern a cutback grade apply to it. Its hazards are thermal, and they are unusually concentrated because this is the grade that ends up on roofs: melted in open kettles at 180 to 200 °C, mopped or poured by hand, and — on torch-applied membranes — worked directly alongside a naked propane flame.
The controls that keep a cutback bitumen crew safe are close to useless here, and the reverse is also true. A cutback such as MC-30 is a solvent problem: kerosene vapour, a flash point that can sit near the air temperature, ignition from a spark at ground level, and a material that is only ever warmed. 85/25 has no solvent at all and a flash point of at least 250 °C, but it is deliberately held at 180 to 200 °C in an open vessel and moved about by hand at a temperature that produces a full-thickness burn on contact. A supervisor who has spent a season on priming work and moves to membrane work is carrying the wrong instincts, and the re-brief before that first shift is not a formality.
Most fires on jobs using 85/25 do not start in the kettle. They start with the propane torch used to bond a torch-applied membrane, or with the burner under the melter, and they take hold in the roof build-up rather than in the binder. Timber decks, bitumen-impregnated fibreboard, old felt layers and — worst of all — combustible insulation inside a warm-roof cavity will accept a flame through a lap or an open detail and smoulder unseen for hours. Three rules follow directly. Keep the torch flame on the membrane roll and off the substrate, and never leave a lit torch resting on the deck. Work to a hot-work permit, and maintain a fire watch on the roof and in the space below it for the full period your local regulation requires after the crew stops — an hour is a common minimum and is often not enough on a void construction. Where the detail is close to a combustible upstand, a cavity opening or a rooflight kerb, stop torching and finish it with hot bitumen from the kettle or with a self-adhesive strip instead.
Bitumen at working temperature sticks on contact and keeps discharging heat into the tissue afterwards, so the burn deepens for some time after the splash itself. Flood the area at once with clean cold running water and keep flooding it for a minimum of 10 to 15 minutes, then keep cooling during transport to medical care. Leave the bitumen in place. Do not pick, scrape or dissolve it off with solvent or fuel — the crust is protecting the wound, and taking it off in the field takes skin with it. Removal is a decision for a clinician. Dress loosely over the top with a clean non-adherent covering, and get medical attention for anything larger than a minor splash, always without exception for the face, the hands and the eyes. Eye contact from a splash or from a steam ejection is a hospital case regardless of how it looks at the time.
85/25 arrives as bags, cartons, blocks or drum slugs, and how they go into the vessel decides most of what happens next. A steam explosion needs no more than a wet package: a small volume of liquid water becomes roughly seventeen hundred times its own volume of steam the instant it meets 190 °C bitumen, and the charge leaves the kettle in a sheet rather than a splash. The controls are unglamorous and they work.
On fire: never put water on burning bitumen. A jet will boil the surface over and carry burning material with it. Keep Class B dry powder or foam extinguishers at the kettle itself, within reach of the operator rather than at the roof edge, and size the provision for the volume being melted.
A fired kettle is never left unattended, and that includes the tea break. Fit a thermometer that is read rather than assumed, and hold the working range instead of chasing it with the burner. Site the vessel on a level non-combustible base, clear of doorways, escape routes, stored materials and gas cylinders, and never inside the building or under a canopy. Leave at least a quarter of the vessel empty so a foaming event has somewhere to expand. On gas-fired units, inspect hose, regulator and connections at the start of each shift and isolate at the cylinder valve — not merely at the burner — whenever the vessel is left.
Hot bitumen gives off fume that stings the eyes and the upper airway, and the output climbs sharply with temperature, which is one more argument against overheating a charge. Stand upwind, do not lean over an open kettle, and force-ventilate whenever the work moves indoors — plant rooms, basement tanking, podium decks under a slab and enclosed stairwell details are the usual places crews get caught. Separately, hydrogen sulphide can collect in the vapour space above heated bulk storage even when the concentration in the product is negligible. Any tank, pit, sump or vessel that has held hot bitumen is a confined space: gas test it, ventilate it and enter it only under permit with a standby person outside.
None of the above displaces the supplier Safety Data Sheet, which governs, or local hot-works and roofing regulation, which is frequently stricter and may mandate permits, fire watch duration and kettle siting distances. Read the SDS before the first pallet is opened rather than after something has gone wrong.
Because 85/25 is a hard solid at ambient temperature and is not tacky to the touch, it can be packed in formats that would be impossible for a paving grade. That widens the choice and changes the landed cost calculation.
| Packing | Net weight per unit | Typical units per 20' FCL | Typical net cargo per FCL | Best suited to |
|---|---|---|---|---|
| Kraft paper bag with meltable liner | 25 kg | about 800 bags, palletised | about 20 MT | Felt plants and membrane lines; the whole bag is charged into the melter with no waste to dispose of |
| Carton box with release liner | 25 kg | about 720–800 cartons | 18–20 MT | Sites with manual handling only; easier stacking and cleaner site storage than bags |
| New steel drum | 180 kg | 80 drums | 14.4 MT | Buyers with drum-handling equipment and a drum decanting or melting unit |
| New steel drum | 150 kg | 80 drums | 12 MT | Markets where 150 kg is the customary drum and manual handling limits apply |
| Jumbo bag | 1 MT | 20 bags | 20 MT | Large melters with crane or forklift access; lowest packing cost per tonne |
It is two different measurements bolted together, not a penetration range — and that is the mistake buyers arriving from paving grades most often make. The 85 is the nominal ring and ball softening point in °C to ASTM D36. The 25 is the nominal needle penetration at 25 °C in tenths of a millimetre to ASTM D5, run with a 100 g needle for 5 seconds. Trade practice allows roughly ±5 on each, which puts the material at 80 to 90 °C and 20 to 30 dmm. A quick way to tell the conventions apart: in a blown designation the first number is much larger than the second, whereas a penetration grade such as 60/70 quotes the two ends of one single measurement.
Because ASTM D113 does not discriminate between good and bad blown material. Air blowing converts the binder from a sol to a gel structure, so at 25 °C it behaves as a stiff elastic solid and breaks after only a few centimetres regardless of batch quality. No roofing failure mode corresponds to slow tensile elongation at 25 °C, and the test is poorly reproducible at this consistency. Use penetration at 0 °C, the calculated penetration index, or a sag test on the finished membrane instead.
They have similar penetration but completely different heat resistance. A straight-run 20/30 softens in the high 50s to low 60s °C; a blown 85/25 softens at 80 to 90 °C. Air blowing has added roughly 20 to 30 °C of heat resistance at the same room-temperature consistency, and has raised the penetration index from about 0 to about +3. The two are not interchangeable in either direction.
No. It is an industrial grade and is not designed as a paving binder. Its gel structure and low ductility mean it lacks the cohesion and fatigue behaviour a pavement needs, and it is too stiff to coat aggregate properly at normal mixing temperatures. For hot-mix asphalt use a penetration, viscosity or performance grade. Blown bitumen also has no place as an extender in paving binder.
90/15 is both slightly more heat resistant (softening point 85 to 95 °C) and considerably harder (penetration 10 to 20 dmm). It is chosen for pipe coating, sound-deadening and insulating compounds and for membranes in very hot climates. 85/25 is softer, easier to work, better at saturating felt and better at accommodating deck movement, which is why it dominates roofing volumes.
Melt and work it at roughly 180 to 200 °C, which is about 100 °C above its own softening point and is what a blown grade needs before it will flow and wet a surface properly. That range sits 50 to 70 °C below the 250 °C specified minimum flash point. Around 230 °C is a hard stop, not an operating temperature — it leaves only some 20 °C under that minimum, and although most batches flash well above 250 °C, the only figure your contract entitles you to is the specified minimum. The second half of the answer matters more in practice than the first: time at temperature does the same damage as excess temperature. Hold a charge hot for hours and the oxidation reaction simply continues, lifting the softening point and dropping the penetration until the material no longer meets the band you paid for. Melt what the shift will consume.
Not automatically, and the reason is a gap in the standard rather than a defect in the material. ASTM D312 Type III covers roughly 85 to 96 °C softening point with penetration at 25 °C of about 15 to 35 dmm, while the type below it stops around 80 °C. The 85/25 band of 80 to 90 °C straddles the interval between them: a batch testing 87 °C certifies comfortably as Type III, but a batch testing 82 °C is fully in grade as 85/25 and fits no D312 type at all. So if a project, an insurer or a membrane manufacturer names a D312 type, buy against the type rather than the trade designation — write the softening point floor into the purchase contract and require D312's full test set, including its nominal ductility minimum, on the batch Certificate of Analysis. Verify the limits against the current edition of D312, since the edition named in your contract is the one that governs.
There is no meaningful expiry date on the binder itself. A material already blown to an 85 °C softening point oxidises so slowly at ambient temperature that storage time is not the limiting factor — the packaging is. What actually ends a consignment is a split bag, a corroded drum seam or a pallet that has been standing in water, because trapped water is exactly what turns a routine charge into a kettle ejection. Store under cover, off the ground and out of direct sun, and judge the material by inspection before charging rather than by a date on a label. One caution that is specific to blown grades: the specification does move with reheating. A charge that is melted, left to cool in the vessel and melted again has taken two rounds of oxidation and will no longer test the same as the drum it came out of.
Send quantity, packing format, destination port and Incoterm. Tell us whether the material is going into a felt line, a membrane plant or site-applied waterproofing, and whether you need the batch to sit in the upper half of the softening point band — both affect which batch is allocated.