Four different materials are sold under the heading roofing bitumen, and a purchase order that does not say which one is being bought is the start of most roofing supply disputes.
Ask three buyers what roofing bitumen is and you will get three answers, all of them correct. The term is a function, not a specification. In practice it covers four distinct material streams that arrive at the same roof by different routes:
The governing number is the softening point against the temperature the roof actually reaches. A dark bituminous roof surface under strong sun is commonly measured at 70 to 80 °C, well above ambient air temperature. A paving binder such as bitumen 60/70 has a ring-and-ball softening point of 49 to 56 °C. On a roof it is not merely soft, it is past the point at which it holds position: it creeps down slope, bleeds through the surfacing and picks up under foot traffic. Oxidized bitumen at 85 to 100 °C softening point is still below its softening point on the same roof on the same afternoon. That single property — staying where it was placed on a warm slope — is the whole reason the roofing industry blows bitumen rather than simply buying a harder distillation cut.
Heat resistance alone is easy to buy. A roof also moves. Decks deflect, structures expand and contract on a daily thermal cycle, and every joint, upstand and penetration concentrates that movement into a small area of membrane. The material has to resist flow at 80 °C and still tolerate strain at 0 °C or below, and those two demands pull in opposite directions. Every grade decision on this page is a trade between them. It is also why polymer modification exists: SBS and APP break the trade-off in a way that blowing alone cannot.
The bitumen itself is classified under HS 2713.20, petroleum bitumen, wherever it moves as drums, bags or bulk. The finished product a membrane plant makes from it — reinforced bitumen sheet in rolls — is an article of asphalt and normally falls under a different heading, commonly 6807. Buyers who import raw bitumen and export finished membrane are working two customs classifications, two duty positions and often two documentation sets. Confirm both with your broker before the first shipment rather than after it.
ASTM D312 is the specification for asphalt used in built-up roofing. It divides the material into four types by softening point, and the type is selected by the slope of the roof it is going on. The penetration limits at three temperatures are what separate a genuine D312 asphalt from a commercial grade that merely has a similar softening point.
| Type | Softening point, ASTM D36 | Penetration at 25 °C (100 g, 5 s) | Penetration at 0 °C, min (200 g, 60 s) | Penetration at 46 °C, max (50 g, 5 s) | Maximum roof slope |
|---|---|---|---|---|---|
| Type I | 57–66 °C | 18–60 dmm | 3 dmm | 90 dmm | up to 1/2 in per ft (about 4 %) |
| Type II | 70–80 °C | 18–40 dmm | 6 dmm | 100 dmm | up to 1 1/2 in per ft (about 12 %) |
| Type III | 85–96 °C | 15–35 dmm | 6 dmm | 90 dmm | up to 3 in per ft (about 25 %) |
| Type IV | 99–107 °C | 12–25 dmm | 6 dmm | 75 dmm | up to 6 in per ft (about 50 %) |
Hot roofing asphalt is not applied at a fixed temperature. It is applied at the temperature where it reaches a defined viscosity, and that temperature is different for every batch.
The equiviscous temperature (EVT) is the temperature at which a roofing asphalt reaches the viscosity at which it can actually be spread at the intended rate. It is defined at two viscosity points because there are two ways of putting it down:
A given batch therefore has two EVT figures, and the spreader EVT is the higher temperature of the two because the asphalt has to be thinner to reach the lower viscosity.
This is worth stating plainly because it appears on site paperwork constantly. The centistoke (cSt) is a unit of kinematic viscosity. The centipoise (cP) is a unit of dynamic viscosity. They are related by density:
kinematic viscosity (cSt) = dynamic viscosity (cP) ÷ density (g/cm³)Bitumen expands appreciably on heating, so roofing asphalt at application temperature has a density in the region of 0.92 to 0.95 g/cm³ rather than the 1.00 to 1.05 it shows at 25 °C. A rotational viscometer reading of 125 cP taken to ASTM D4402 therefore corresponds to something in the order of 130 to 135 cSt for the same material at the same temperature — it is more viscous than the mop target, and the true EVT is a few degrees higher than the temperature at which the instrument read 125. Treating a cP number as though it were a cSt number therefore pushes the crew into applying cold, which is exactly the error that produces thin, patchy interply moppings. Kinematic viscosity of asphalts is determined directly by ASTM D2170; where a rotational instrument is used instead, the conversion has to be made explicitly with the density at test temperature.
Nothing in the grade name predicts EVT. Softening point and penetration describe the consistency of the material at 25 °C and at the ring-and-ball temperature. EVT is a property in the region of 200 to 240 °C, on a different part of the viscosity–temperature curve, and it is set by the crude slate of the feedstock and by how the batch was blown. Two consignments both correctly labelled 95/25, both inside their softening point and penetration bands, can have meaningfully different EVTs. It is not a figure that can be inferred, looked up in a table or carried over from the last job.
Ask for the EVT on the technical data sheet, on the container label and, where it can be arranged, on the delivery paperwork with the batch reference. Ask for the finished blowing temperature (FBT) at the same time — it is the temperature at which blowing was stopped and it is the practical ceiling for every heating operation downstream, because heating above it begins to reverse the reaction, drops the softening point and raises fume sharply. A producer who cannot supply EVT and FBT is selling you a grade name, not a roofing asphalt.
The EVT window applies at the point of application, not in the kettle. Common practice is to keep the asphalt within about 14 °C (25 °F) of the EVT when it reaches the mop or the spreader. Between kettle and roof the material loses heat in the transfer line, the bucket or the mop cart, in the hoist, and again across the roof surface on a cold or windy day. The kettle setting has to be higher than the EVT to compensate, and how much higher is a site-specific measurement, not a rule. Take a thermometer reading in the mop cart, not only at the kettle. A widely used North American site rule is that mopping asphalt should still be at least 218 °C (425 °F) where it touches the felt.
A built-up roof is a laminate constructed in place: alternating layers of felt and hot asphalt, with the asphalt doing the waterproofing and the felt holding it in position and controlling its thickness. The quantities below are the industry reference rates and they are what turn a roof area into a purchase order.
The deck must be sound, dry and correctly sloped to drainage. Moisture trapped under a hot-applied system has nowhere to go: it becomes steam under the first mopping and a blister thereafter. Slope is decided here and it determines which ASTM D312 type is legitimate for the rest of the job — no later decision can correct a Type I asphalt on a 20 % slope.
Mechanically fastened or set in asphalt depending on deck type. Common base sheets are asphalt-coated glass fibre to ASTM D4601 and asphalt-saturated organic felt to ASTM D226. On a nailable deck the base sheet is normally fastened rather than mopped, so that the first hot mopping is not fighting deck movement.
Establish the EVT for the batch being used from the producer data sheet, set the kettle above it to allow for transfer losses, and verify the thermometer before lighting. Record the temperature at the mop cart, not only at the kettle. Charge the kettle for the day's work, not for the week's.
The reference rate for an interply mopping is about 1.2 kg/m², that is 25 lb per 100 ft², with a tolerance commonly taken as ±20 %. Plies are shingled so that each sheet overlaps the one below by the fraction that gives the specified ply count — a four-ply roof is built from sheets lapped so that any cut through the assembly crosses four layers of felt. Every ply is set into a continuous mopping while the asphalt is still hot enough to wet the felt.
A gravel-surfaced roof receives a flood coat of about 2.9 kg/m² (60 lb per 100 ft²) into which the aggregate is embedded while hot — roughly 20 kg/m² of gravel or about 15 kg/m² of slag at the customary 400 and 300 lb per 100 ft². Smooth-surfaced roofs take a glaze coat instead and rely on a surfacing sheet or a reflective coating for UV protection.
Base flashings, cants, reglets, drains and penetrations are where built-up roofs fail, not the field. They take more asphalt per square metre than the field, more labour and more attention. Verify the finished assembly by cut test: a small core through the membrane shows the ply count, the continuity of each mopping and whether the interply bond actually formed.
Add the moppings. A four-ply gravel-surfaced roof takes roughly four interply moppings at 1.2 kg/m² plus a 2.9 kg/m² flood coat, so on the order of 7 to 8 kg of asphalt per square metre of field area, before flashings and waste. A 10,000 m² roof is therefore in the region of 70 to 80 tonnes, which is five to six 20-foot containers of 180 kg drums at 14.4 MT each. Add an allowance for detail work and for kettle residue before ordering.
Grade selection runs on two questions in order: how steep is the roof, and how hot does its surface get. Cold climates then impose a third constraint from the other direction. The commercial grades below are the ones actually traded for roofing work.
| Grade | Softening point, ASTM D36 | Nearest ASTM D312 band | Roofing use and climate | What limits it |
|---|---|---|---|---|
| 75/25 | 70–80 °C | Type II softening point band | Dead-level and low-slope BUR mopping, damp-proof course work and general hot-applied waterproofing in temperate climates | Slumps on any real slope under strong sun; unsuitable as an exposed coating grade in desert or tropical conditions |
| 85/25 | 80–90 °C | Straddles Type II and Type III | The general-purpose membrane coating and BUR grade for temperate to warm climates | Sits across a type boundary, so a batch can fall either side of it. Never quote a D312 type from the grade name alone |
| 90/15 | 85–95 °C | Type III softening point band | Hot climates and steeper slopes, hard coating compounds, mastics and detail work | Nominal penetration of 10–20 dmm can fall below the D312 Type III minimum of 15 dmm — check the batch penetration, not the label |
| 95/25 | 90–100 °C | Type III softening point band | Hot-climate roofing and membrane coating where slump resistance is the governing requirement | Can test above the 96 °C Type III ceiling and into no man's land between Types III and IV |
| 105/35 | 100–110 °C | Type IV softening point band | Very hot exposures and steep slopes, expansion joint filler, upstands and flashing compounds | Low-temperature flexibility drops sharply; a poor choice anywhere the roof sees a real winter |
| 115/15 | 110–120 °C | Above Type IV — outside the standard | Not a roofing membrane grade. Pipe-coating enamel and hard industrial work | Too brittle to accommodate roof movement; see bitumen enamel grade |
A prefabricated bitumen membrane is a sandwich, and each layer of it is a different bitumen bought against a different requirement.
The reinforcement carries the sheet through the plant and carries the stress in service. Three families dominate. Organic felt, covered by ASTM D226 as Type I and Type II — the felts historically named No. 15 and No. 30 for their mass per 100 ft² — is cellulose based, absorbent and now largely confined to base sheet and repair work. Glass fibre, covered by ASTM D2178 as Type IV and Type VI, gives dimensional stability, low elongation and good fire performance. Non-woven polyester gives high elongation, puncture resistance and tear strength and is the standard carrier for modified sheets in movement-critical positions. Composite carriers combine glass strands with polyester to get stability and elongation in one mat.
Saturation applies only to absorbent carriers. The dry felt runs through a saturator tank of hot bitumen and takes the material up into the fibre mat. The requirement here is the opposite of everything else on this page: the saturant must be soft, low in viscosity at saturation temperature and highly penetrative — its softening point sits well below that of any coating grade and its penetration well above — because the objective is impregnation of the mat rather than a film on its surface. A saturant with too high a softening point sits on the outside of the felt, leaves the core dry, and produces a sheet that wicks water along the reinforcement — a defect that never shows on the finished roll and always shows on the roof. Glass and polyester carriers are not saturated in this sense; they are coated directly, and the plant's saturant tank sits idle when the line is running them.
The coating is what the weather actually meets. It is a harder blown grade — most commonly 85/25 or 95/25 for conventional oxidized sheet — blended with mineral stabiliser and applied to both faces of the carrier in a coating pan, then calendered to the specified thickness. Typical filler loadings are of the order of 30 to 40 % by mass of the coating compound, drawn from limestone, dolomite, slate dust or talc. The filler is not an adulterant. It raises viscosity so the coating holds thickness on the sheet, raises the effective softening point and resistance to flow, improves fire behaviour, gives the surfacing granules something to key into, and reduces cost per square metre. What it does not do is add flexibility, so an over-filled compound produces a stiff sheet that cracks at the roll edge.
The top face is finished with mineral granules for UV protection and appearance, or with sand, talc or a thin polyethylene film where the sheet will be covered or overlaid. The underside of a torch grade carries a burn-off film that melts under the flame and tells the operator the compound underneath has reached working temperature — it is a process control, not packaging.
This is where buyers most often get the raw material wrong. For an SBS-modified compound the base bitumen is a soft paving grade, not an oxidized one. SBS works by absorbing the maltene fraction of the bitumen and swelling into a continuous elastomeric network, and it needs an aromatic, maltene-rich base to do that. Oxidized bitumen has had most of its maltenes converted to asphaltenes during blowing, which is precisely why it is heat resistant — and precisely why SBS will not disperse properly in it. Trying to modify a blown grade produces a compound that separates on storage and delivers neither the heat resistance of the oxidized grade nor the elasticity of the polymer. Compounds are typically prepared in a high-shear mill at around 180 to 190 °C with sufficient residence time for the polymer to swell fully, then held under agitation. Typical loadings run in the order of 10 to 15 % SBS or 25 to 30 % APP by mass of the compound; the finished sheet is specified by performance, not by polymer content, so treat those figures as orientation rather than a purchase specification.
The practical consequence for procurement is simple: a plant making oxidized sheet buys blown grades, and a plant making SBS sheet buys soft penetration grade bitumen plus polymer. A plant making both buys both, and must keep them in separate tanks. Oxidized and paving bitumen co-mingled in storage produce a blend that satisfies neither specification.
Both are torch-applied bitumen membranes and both look similar on the roll. They behave differently in every way that matters, and specifying one and receiving the other is a substitution, not an equivalence.
| Property | APP — plastomeric | SBS — elastomeric |
|---|---|---|
| Polymer | Atactic polypropylene and related polyolefins — a thermoplastic | Styrene-butadiene-styrene block copolymer — a thermoplastic elastomer |
| How it modifies the bitumen | Forms a continuous plastomeric phase; the compound behaves as a filled plastic | Swells in the maltene phase and forms an elastic three-dimensional network; the compound behaves as a rubber |
| Typical polymer loading | Around 25–30 % by mass of the compound | Around 10–15 % by mass of the compound |
| Behaviour under strain | Plastic — deforms and stays deformed | Elastic — recovers substantially after the load is removed |
| Heat and flow resistance | The strong point. Compound softening points are commonly quoted around 150 °C | Good but lower. Commonly quoted around 110–125 °C |
| Low-temperature flexibility | The weak point. Cold-bend limits commonly around −5 to −15 °C | The strong point. Cold-bend limits commonly −20 °C and below |
| Elastic recovery / movement tolerance | Essentially none — relies on the carrier for movement | Substantial — accommodates thermal cycling and structural movement |
| Application methods | Torch-applied or hot-air welded. Not compatible with hot asphalt mopping | Torch-applied, hot mopped in asphalt, cold adhesive or self-adhered |
| Best suited to | Hot climates, high solar exposure, roofs where slump and flow resistance dominate | Cold and temperate climates, roofs with movement, seismic zones, and any cold-applied or self-adhered system |
| ASTM product specifications | D6222 (polyester reinforced), D6223 (composite reinforced), D6509 (glass base sheet) | D6162 (composite), D6163 (glass), D6164 (polyester) |
| European framework | EN 13707 product standard; EN 1110 flow resistance at elevated temperature | EN 13707 product standard; EN 1109 flexibility at low temperature |
Roofing is the application in which bitumen is worked closest to its flash point, in an occupied building, by hand. The controls below are not general advice — each one addresses a specific and recurring failure.
A volume of liquid water becomes something like 1,700 volumes of steam the instant it meets bitumen at working temperature. The charge does not splash — it leaves the vessel as a sheet. What makes that a roofing problem in particular is where the sheet lands: a working deck with a parapet on one side, an open edge on another, other trades in the space below, and a crew that cannot step back more than a metre or two. The sources are few and specific — rain standing in a drum rim or chime, a mop cart or bucket left out overnight, a block that has sat on wet ground, condensate in a transfer line nobody drained. Check and dry each of them before charging. Introduce material against the wall of the vessel and above the level of the melt, never plunged beneath it. Cover the kettle when it rains, and treat a vessel that has stood open through a shower as suspect until it has been inspected rather than simply relighting it.
Torch work moves the ignition source from the kettle to the membrane and into the building envelope. Roofing torch fires characteristically start hours after the crew has left, in a cavity nobody could see.
Roofing fume is not a nuisance smell; it is the exposure the epidemiology was actually written about. IARC reviewed it in Monograph Volume 103 (2013) and placed occupational exposure to oxidised bitumens and their emissions during roofing in Group 2A, probably carcinogenic to humans. Emissions from straight-run bitumen during road paving sit one step lower, in Group 2B. The honest reading of that is control rather than avoidance, and the single most effective control is temperature, because fume output climbs steeply with every extra degree. Holding the asphalt at the cool end of the workable EVT window is therefore a health measure and a quality measure at the same time, which is unusual and worth exploiting. Beyond temperature: position the kettle and the crew so the plume travels away from the working face rather than across it, extract mechanically wherever the work is enclosed or indoors, take skin contamination off with a bitumen hand cleaner formulated for the purpose rather than with solvent or fuel, and change out of contaminated clothing at the end of the shift instead of wearing it home.
A bitumen burn is characteristically deeper than the mark on the overalls suggests. The material adheres on contact and keeps discharging heat into the tissue for as long as it stays hot, so the injury goes on developing after the splash itself is over. That makes the response a question of heat removal, not of cleaning the wound. Cool the affected area immediately with clean cold running water for at least 20 minutes, and keep cooling while the casualty is brought off the roof and moved. Never peel or solvent-strip adhered bitumen. Once it has cooled, the adhered layer is a sterile covering over the burn, and lifting it takes the skin underneath with it. Removal is a clinical decision taken in a burns unit, and no part of it belongs on a roof. Treat anything beyond a trivial splash — and every burn involving the face, hands or eyes — as a case for medical assessment.
The protective equipment that prevents most of these is unremarkable and routinely got wrong. A face shield over safety glasses for charging, decanting and any overhead detail. Heat-resistant gauntlets long enough to cover the forearm and worn outside the sleeve, so a splash runs off instead of down inside the glove. Cotton or treated overalls with no synthetic layer anywhere underneath, because synthetics melt into the wound and turn a survivable burn into a graft. Trousers over the boot rather than tucked in, and no exposed laces for hot material to lodge in.
Roofing asphalt is bought in whichever format the melting equipment on the receiving end can actually take, and that is a question to settle before the enquiry goes out rather than when the container is on the ground.
It is a category rather than a single product. It covers hot-applied built-up roofing asphalt classified by ASTM D312 into Types I to IV, the soft saturant bitumen that impregnates a felt carrier in a membrane plant, the harder filled coating grade applied over that carrier, and the APP or SBS modified compound used in torch-applied and self-adhered rolls. All of them resist flow at roof surface temperatures far above what a paving binder can tolerate, which is why roofing uses blown and polymer-modified bitumen rather than penetration grade.
EVT is the temperature at which a roofing asphalt reaches the viscosity needed to spread at the design rate: 125 centistokes for mop application and 75 centistokes for a mechanical spreader. It is specific to the batch, because it depends on the feedstock and on how far that batch was blown, and it cannot be inferred from the grade name or from softening point and penetration. It has to come from the producer's technical data sheet or the container label. Ask for the finished blowing temperature at the same time, because that is the ceiling for every heating operation downstream.
Centistokes. EVT is defined on kinematic viscosity, and centistokes and centipoise are not the same unit. Kinematic viscosity in cSt equals dynamic viscosity in cP divided by density in g/cm³, and roofing asphalt at application temperature sits around 0.92 to 0.95 g/cm³ rather than 1.00. A rotational viscometer reading of 125 cP to ASTM D4402 therefore corresponds to something in the order of 130 to 135 cSt for the same material, so treating the two as interchangeable pushes the crew into applying a few degrees cold. Where a cP instrument is used, convert explicitly using the density at test temperature.
APP is atactic polypropylene, a plastomer. It makes a stiffer sheet with better heat and flow resistance, commonly quoted around 150 °C softening point for the compound, and it has essentially no elastic recovery. SBS is styrene-butadiene-styrene, an elastomer. It makes a rubbery sheet with far better low-temperature flexibility, commonly down to −20 °C and below, and it recovers elastically after deformation. APP suits hot climates and high solar exposure; SBS suits cold and temperate climates and any roof with real movement. APP is torch-applied or hot-air welded and is not compatible with hot asphalt mopping, while SBS can be torched, mopped, cold-adhered or self-adhered.
Start from slope, then from the surface temperature the roof will actually reach, which for a dark membrane in strong sun runs 30 to 40 °C above air temperature. For hot climates and steeper slopes 90/15 and 95/25 sit in the ASTM D312 Type III softening point band and give the slump resistance needed. 85/25 remains the general-purpose grade for temperate to warm conditions. Going harder than the slope requires buys nothing and costs low-temperature flexibility. Be careful with the mapping: a commercial grade name is not a certification against D312, since 90/15 can fall below the Type III minimum penetration of 15 dmm and 95/25 can test above the 96 °C ceiling.
No, not as the waterproofing layer. A 60/70 paving binder has a ring-and-ball softening point of 49 to 56 °C, and a dark roof surface in sun is commonly 70 to 80 °C. The binder is past its softening point in service: it creeps down slope, bleeds through the surfacing and picks up under foot traffic. Soft paving grades do have a legitimate role in roofing, but on the factory side rather than the roof — they are the base bitumen for SBS-modified membrane compound, because SBS needs a maltene-rich bitumen to swell in and will not disperse properly in a blown grade.
Work from the reference rates. An interply mopping is about 1.2 kg/m², that is 25 lb per 100 ft², commonly with a ±20 % tolerance, and a flood coat for a gravel-surfaced roof is about 2.9 kg/m² or 60 lb per 100 ft². A four-ply gravel-surfaced roof therefore takes roughly 7 to 8 kg/m² of asphalt across the field, so 10,000 m² is in the region of 70 to 80 tonnes — about five to six 20-foot containers of 180 kg drums at 14.4 MT each. Add an allowance for flashings and details, which consume more per square metre than the field, and for kettle residue.
Cool the affected area immediately with clean cold running water for at least 20 minutes, and keep cooling while the casualty is moved. Never peel or solvent-strip adhered bitumen — once cooled it forms a sterile covering and pulling it away takes skin with it. Removal is a clinical decision made in a burns unit, not on site. Because hot bitumen adheres and keeps transferring heat after contact, these burns are consistently deeper than the size of the splash suggests, so treat every one of them as requiring medical assessment.
Most roofing bitumen today is not applied as a bucket of hot binder but as a factory-made sheet.
Send the grade or the ASTM D312 type, the quantity, packing and destination port with your Incoterm. Say whether the material is for site kettle work or for a membrane line, because the saturant, coating and modified-compound requirements are different, and the offer will be built against the one you actually need.