Different Types and Grades of Bitumen Emulsion

Bitumen emulsion comes in two main groups. The first group depends on the electric charge of the bitumen drops: cationic, anionic or non-ionic. The second group depends on how fast the emulsion sets after you spray it: rapid, medium or slow.

Put the two together and you get names like RS-1, SS-1h or HFMS-2. This guide explains what each type does and what the names stand for. It also gives a spec table for each grade, so you can compare the numbers and pick the right one. If you want to start with the basics, read our guide to bitumen emulsion.

Types of Bitumen Emulsion

Every bitumen emulsion needs an emulsifier. It is a chemical that keeps the small bitumen drops separate in water. The emulsifier also gives these drops a positive or negative charge. This charge affects how the emulsion sets.

Bitumen emulsions are first classified by their electrical charge. Cationic emulsions have a positive charge, while anionic emulsions have a negative charge. Non-ionic emulsions have no charge.

Emulsions can also be classified by how quickly they set. Cationic and anionic emulsions are commonly grouped as rapid-setting (RS), medium-setting (MS), or slow-setting (SS). Letters and numbers at the end of the grade name provide further details about the product.

Bitumen Emulsion Types at a Glance

Charge	Rapid setting	Medium setting	Slow setting
Cationic	CRS-1, CRS-2, K1-60	CMS-2, CMS-2h	CSS-1, CSS-1h
Anionic	RS-1, RS-2, HFRS-2	MS-1, MS-2, MS-2h, HFMS-1, HFMS-2, HFMS-2h, HFMS-2s	SS-1, SS-1h

What are Cationic, Anionic, and Non-ionic Bitumen Emulsions? 

Bitumen emulsion is made by mixing hot bitumen, water, and an emulsifier. The mixture passes through a mill, where the bitumen breaks into very small drops. The emulsifier gives these drops an electrical charge.

The type of emulsifier determines the charge of the bitumen drops. This creates cationic, anionic, or non-ionic emulsions.

The charge is important because it affects how the emulsion interacts with the road surface. The main types are:

• Cationic emulsions
• Anionic emulsions
• Non-ionic emulsions
• Clay-stabilized emulsions

Cationic Bitumen Emulsion

Cationic emulsions have a positive charge. Many road stones, including granite and quartz, have a negative surface charge. This helps the bitumen drops attach to the stone.

Cationic emulsions can also work well when the stone is damp. For this reason, they are widely used in road construction and repair.

For more details, see our guide to cationic bitumen emulsion.

Anionic Bitumen Emulsion

Anionic emulsions have a negative charge. They are commonly used with stones such as limestone and marble.

Anionic emulsions mainly set as the water leaves the emulsion. They therefore perform better in warm and dry conditions.

Anionic grades do not have a letter before the grade name. Common grades include RS-1, RS-2, MS-1, MS-2, MS-2h, SS-1, and SS-1h. High-float grades include HFMS and HFRS. QS-1h is a quick-setting grade.

You can compare the main grades in the anionic specification table.

If you are looking for an "anionic CSS-1h", note that this grade is not anionic. The letter C indicates a cationic emulsion. The equivalent anionic grade is SS-1h.

Non-ionic Bitumen Emulsion

Non-ionic emulsions have no electrical charge. The emulsifier keeps the bitumen drops separate in the water.

Non-ionic emulsions are less common in road applications. They are used for more specific applications, including some cases where the emulsion needs to be mixed with cement.

Clay-stabilized Bitumen Emulsions

Clay-stabilized emulsions use fine clay, such as bentonite, to keep the bitumen drops separate. The clay forms a protective layer around the drops.

These emulsions are mainly used for industrial applications, including some roof coatings. They are not standard road-grade emulsions.

Cationic vs. Anionic: Which One Should You Choose?

The right emulsion depends on the stone, weather, and application.

Cationic emulsions are often suitable for a wide range of road stones and can perform well in damp conditions. Anionic emulsions are commonly used with limestone and marble and generally perform better in warm, dry conditions.

Point	Cationic	Anionic
Drop charge	Positive	Negative
Name	Starts with C (CRS, CMS, CSS)	No letter in front (RS, MS, SS)
Best with	Granite, quartz and most road stone	Limestone and marble
Weather	Works in cool or wet weather	Works best in warm, dry weather
Main standards	ASTM D2397, IS 8887, EN 13808	ASTM D977, IS 3117

Do not mix cationic and anionic emulsions in the same tank or pump. Their opposite charges can cause the emulsion to break.

If the stone type is uncertain, a laboratory compatibility test can help confirm which emulsion is suitable.

How to Test the Charge of an Emulsion

The charge of an emulsion can be tested using two electrodes and a weak electric current.

The electrodes are placed in a sample of the emulsion. After the test, the electrode covered with bitumen shows the type of charge.

Anionic drops move toward the positive electrode, called the anode. Cationic drops move toward the negative electrode, called the cathode. If neither electrode is covered with bitumen, the emulsion is non-ionic.

For more lab methods, see our bitumen emulsion tests guide.

What are Rapid, Medium, and Slow Setting Bitumen Emulsions?

What are Rapid, Medium, and Slow Setting Bitumen Emulsions?

After an emulsion is sprayed, it must "break". This means the water leaves the emulsion and the bitumen drops come together. You can see this process as the color changes from brown to black. The bitumen then bonds to the stone, and the emulsion has set.

The setting speed depends on the emulsifier and the weather. Hot, dry, and windy conditions make the process faster. Cold and wet conditions make it slower. As a result, the same grade may set in minutes on a hot day but take much longer in cold weather.

Rapid Setting Bitumen Emulsion (RS)

Rapid setting emulsions break quickly after they contact the stone. This allows crews to spray the emulsion and place stone chips soon after. They are commonly used for chip seals, surface dressing, and sand seals.

The main grades are RS-1 and RS-2 (anionic), and CRS-1 and CRS-2 (cationic). The number 2 indicates a thicker emulsion than grade 1. This helps it stay in place on sloping roads.

Medium Setting Bitumen Emulsion (MS)

Medium setting emulsions break more slowly. This gives crews more time to mix the emulsion with coarse stone and spread the mix. They are commonly used for cold mix and road patching.

The main grades are MS-1, MS-2, and MS-2h (anionic), and CMS-2 and CMS-2h (cationic).

Slow Setting Bitumen Emulsion (SS)

Slow setting emulsions are the most stable of the three main types. They stay workable long enough to mix with fine stone and sand. Water can also be added when required.

They are used for tack coat, prime coat, fog seal, and slurry seal. Some crews also use them on gravel roads for dust control.

The main grades are SS-1 and SS-1h (anionic), and CSS-1 and CSS-1h (cationic).

RS vs MS vs SS: The Short Comparison

Point	Rapid (RS)	Medium (MS)	Slow (SS)
When it breaks	As soon as it touches stone	After some mixing time	Slowly
Works best with	Clean, coarse stone	Coarse stone for mixing	Fine stone and sand
Can you add water?	No	Rarely	Yes
Main jobs	Chip seal, sand seal	Cold mix, patching	Tack, prime, fog, slurry

So what is the difference between RS-1 and SS-1? RS-1 sets quickly, so it is sprayed before stone is placed on the surface. SS-1 sets more slowly, so it can be mixed with fine material or diluted with water when required.

Bitumen Emulsion Naming Strategy

A bitumen emulsion grade name may look like a code, but each part gives useful information. You can read the name from left to right.

1- Charge. A name that starts with C is cationic. A name with no C at the beginning is anionic. For example, CMS is cationic, while MS is anionic.

2- Setting speed. The next two letters show the setting speed: SS for slow setting, MS for medium setting, and RS for rapid setting.

3- Thickness. The number 1 indicates a thinner emulsion, while 2 indicates a thicker one.

4- Base bitumen. A small "h" means the base bitumen is harder. A small "s" means it is softer. Softer bitumen can be useful in mixes that contain more sand.

How to Read an Emulsion Name

Name	Charge	Setting speed	Thickness	Base bitumen
CSS-1h	Cationic (C)	Slow (SS)	Thin (1)	Hard (h)
RS-2	Anionic (no C)	Rapid (RS)	Thick (2)	Normal
HFMS-2s	Anionic (no C)	Medium (MS)	Thick (2)	Soft (s)

The letters HF mean "high float". These emulsions put a thicker bitumen film on the stone, so the road ages more slowly in the sun. A lab proves this with the float test. We explain it in our guide to the float test.

RS-1, SS-1 and Other Full Forms

Short name	Full form	Charge
RS-1	Rapid Setting-1	Anionic
SS-1	Slow Setting-1	Anionic
MS-2	Medium Setting-2	Anionic
CRS-1	Cationic Rapid Setting-1	Cationic
CMS-2	Cationic Medium Setting-2	Cationic
CSS-1h	Cationic Slow Setting-1, hard	Cationic
HFMS-1	High Float Medium Setting-1	Anionic
QS-1h	Quick Set-1, hard	Anionic

Same Name, Different Standards

The table above follows the American system (ASTM and AASHTO). Other standards may use the same letters differently, so the grade name alone is not always enough.

Standard	How it names emulsions
ASTM D977 / AASHTO M 140 (US)	Anionic: RS-1, RS-2, MS-1, SS-1
ASTM D2397 / AASHTO M 208 (US)	Cationic, with C in front: CRS-1, CSS-1
IS 3117 (India)	Anionic: names like RS-1 and SS-1
IS 8887 (India)	Cationic, but also names like RS-1 and SS-1, with no C
EN 13808 (Europe)	Codes like C60B3: C is cationic, 60 is the % of bitumen, B is bitumen, 3 shows how fast it breaks

In India, for example, a name such as RS-1 can be anionic or cationic, depending on the standard. IS 8887 also uses RS-1 for tack coat applications.

Always check which standard applies to your order. Also check the charge on the product data sheet. You can read more in our guide to international bitumen standards.

Bitumen Emulsion Grades

Here is what each grade does and where it is commonly used.

RS-1 Bitumen Emulsion

RS-1 is a thin, anionic, rapid setting emulsion. It is used for light spray applications where stone is placed soon after spraying, such as sand seals and single seal coats. Some contracts also allow it for tack coat.

RS-2 Bitumen Emulsion

RS-2 is also anionic and rapid setting, but it is thicker than RS-1. It stays in place better on slopes, so it is used for heavier chip seals and sand seals.

MS-1 Bitumen Emulsion

MS-1 is anionic and has a medium setting time. It is used for cold mix and sand seals. With water added, it can also be used for fog seals and tack coats.

MS-2 Bitumen Emulsion

MS-2 is thicker than MS-1. It works well in coarse mixes, so it is used for cold mix and patching. MS-2h is the harder version of this grade.

SS-1 Bitumen Emulsion

SS-1 is anionic, slow setting, and thin. SS-1h is the harder version. Both grades can be mixed with fine stone or diluted with water. They are used for tack coat, prime coat, and fog seal.

CRS-1 Bitumen Emulsion

CRS-1 is a cationic, rapid setting emulsion. It is mainly used for tack coat and light surface treatments.

A tack coat is a thin layer sprayed on existing pavement before a new asphalt layer is placed. It helps the two layers bond together.

On a stone base, the first spray is called a prime coat. Slow setting grades are commonly used for this application. Read our full CRS-1 guide or see the CRS-1 product page.

CRS-2 Bitumen Emulsion

CRS-2 is thicker than CRS-1. It is commonly used for chip seals and sand seals.

So what is the difference between CRS-1 and CRS-2? CRS-1 is thinner and is suitable for lighter applications such as tack coat. CRS-2 is thicker and stays in place better, so it is more suitable for chip seals. You can find supply details on our CRS-2 product page.

CSS-1 Bitumen Emulsion

CSS-1 is cationic and slow setting. It is a versatile slow setting grade. It is used for prime coat, tack coat, fog seal, slurry seal, and some pipe coating applications. Read our CSS-1 guide or see the CSS-1 product page.

CSS-1h Bitumen Emulsion

CSS-1h is the harder version of CSS-1. It can be mixed with sand to make slurry seal, a thin layer that protects the road surface. It is also used for fog seal, prime coat, and tack coat. Read more on our CSS-1h page.

HFMS and HFRS Grades

High float grades are anionic. HFMS-1, HFMS-2, HFMS-2h, and HFMS-2s are medium setting grades. HFRS-2 is rapid setting.

These grades form a thicker bitumen film and can perform well in hot conditions. The small "h" means a hard base bitumen, while "s" means a soft base bitumen. HFMS-2s is suitable for mixes that contain sand.

K1-60 Bitumen Emulsion

K1-60 is cationic and rapid setting. It is mainly used for tack coat and surface treatments such as sand seals. Our K1-60 guide and K1-60 product page have the details.

K1-70, K1-40, CRS-60 and CRS-70 (Trade Grades)

Some markets, mainly in Africa, the Gulf, and parts of Asia, buy emulsions under names such as K1-40, K1-60, K1-70, CRS-60, and CRS-70.

In these names, the number usually indicates the bitumen content as a percentage. Naming can vary between suppliers, so always check the product data sheet before ordering.

Supply details are available on our K1-70 and K1-40 pages.

Bitumen Emulsion Specifications

Each grade must pass laboratory tests before it can be sold. The two tables below show the main values for each grade. We have kept three main values for each grade because they help explain the differences between grades.

Here is what these values mean. Thickness, also called viscosity, is measured in SFS (Saybolt Furol seconds). It shows how long the emulsion takes to flow through a standard cup. A higher number means a thicker emulsion.

"Bitumen left after drying" shows how much bitumen remains after the water and other volatile parts leave the emulsion.

Penetration shows how hard the remaining bitumen is. A standard needle is used for the test. A lower penetration value means harder bitumen

Anionic Grades: Specification Table

Grade	Thickness (SFS)	Bitumen left after drying (min.)	Penetration of that bitumen	Extra limits
RS-1	20–100 at 25 °C	55%	100–200	Demulsibility 60% min.
RS-2	75–400 at 50 °C	63%	100–200	Demulsibility 60% min.
MS-1	20–100 at 25 °C	55%	100–200	–
MS-2	100 min. at 25 °C	65%	100–200	–
MS-2h	100 min. at 25 °C	65%	40–90	–
SS-1	20–100 at 25 °C	57%	100–200	Cement mixing 2% max.
SS-1h	20–100 at 25 °C	57%	40–90	Cement mixing 2% max.
HFMS-1	20–100 at 25 °C	55%	100–200	Float test 1,200 s min.
HFMS-2	100 min. at 25 °C	65%	100–200	Float test 1,200 s min.
HFMS-2h	100 min. at 25 °C	65%	40–90	Float test 1,200 s min.
HFMS-2s	50 min. at 25 °C	65%	200 min.	Float test 1,200 s min.; solvent 1–7%
HFRS-2	100–400 at 50 °C	63%	100–200	Demulsibility 60% min.; float test 1,200 s min.

Cationic and K Grades: Specification Table

Grade	Thickness (SFS)	Bitumen left after drying (min.)	Penetration of that bitumen	Extra limits
CRS-1	20 min. at 50 °C	63%	50 min.	–
CRS-2	100–400 at 50 °C	65%	100–250	Oil 3% max.; demulsibility 40% min.
CMS-2	50–450 at 50 °C	65%	100–250	Oil 12% max.
CMS-2h	40–450 at 50 °C	65%	40–90	Oil 12% max.
CSS-1	20 min. at 50 °C	60%	50 min.	Oil 8% max.
CSS-1h	20–100 at 50 °C	57%	40–90	Cement mixing 2% max.
K1-40	25 max. at 25 °C	37%	60–200	–
K1-60	20 min. at 50 °C	63%	50 min.	–
K1-70	20 min. at 50 °C	67%	60–250	Oil 4% max.; ductility 20 cm min.

All grades in both tables also share these limits: storage stability 1% max. after 24 hours, sieve test 0.1% max., solubility in trichloroethylene 97.5% min., and a residue ductility of 40 cm min. (K1-70: 20 cm; K1-40: not tested). Anionic grades must show a negative charge, and cationic grades a positive charge. "Oil" means the oil distillate that remains in the emulsion.

Limits can vary between editions of a standard and between suppliers. Always check the project specification before you order. To see how these laboratory tests are performed, read our bitumen emulsion tests guide.

Which Bitumen Emulsion Grade for Which Job?

Start with the job. Then consider the stone and the weather conditions.

Job	What it is	Best grades	Why
Tack coat	A thin sticky layer between old and new asphalt	SS-1h, CSS-1h; sometimes CRS-1 or RS-1	Slow grades spread evenly and take water
Prime coat	A spray on a stone base before asphalt goes on	SS-1, CSS-1	Thin, so it soaks into the base
Fog seal	A light spray that seals an old, dry road	SS-1h, CSS-1h	Slow grades with water make a light film
Chip seal	Emulsion sprayed first, then a layer of stone chips	CRS-2, RS-2, HFRS-2	Thick and breaks on contact, so chips stay in place
Slurry seal	A thin layer of emulsion, sand and filler	CSS-1h, SS-1h	Slow break gives time to mix
Cold mix and patching	Emulsion mixed with stone without heating	MS-1, MS-2, CMS-2, HFMS-2	Medium break gives time to mix and lay

For the full list of uses, read our guide to bitumen emulsion applications in road construction, repair and maintenance. If you want to compare cold mix with hot mix, see hot mix and cold mix asphalt.

Dilution: Tack Coat, Prime Coat and Fog Seal

Only slow setting grades can normally be diluted with water. Do not add water to rapid setting grades. The following ratios are commonly used in US guides:

Job	Water to emulsion
Tack coat	About 1 : 1
Prime coat	From 1 : 1 up to about 5 : 1, depending on the base
Fog seal	Diluted slow setting emulsion, as your supplier or project says

Your project specification always has the final say. It is also better to ask your supplier to dilute the emulsion at the plant and test a small section before full application.

Three basic rules apply to most jobs. Spray a thin, even layer. Do not spray on a frozen road. Wait until the color changes from brown to black before placing asphalt on top.

For tanks and handling, see storage and handling of bitumen emulsion.

Need Help Choosing a Grade?

If you are not sure which emulsion fits your stone, weather, and application, tell us about your project. We can suggest a suitable grade and provide the relevant data sheet.

We supply bitumen emulsion in drums, IBC tanks, and flexi tanks. See our bitumen emulsion products, check the bitumen emulsion price, or contact us.

FAQ

What are the full forms of RS-1 and SS-1?

RS-1 means Rapid Setting-1, and SS-1 means Slow Setting-1. The number 1 shows a thin emulsion. In the US system both are anionic. In India the same names appear in two standards, an anionic one (IS 3117) and a cationic one (IS 8887), so always check the charge on the data sheet.

Do I need to heat bitumen emulsion before use?

Most grades work at normal temperature, and crews can spray thin grades with a hand sprayer that way. With a distributor truck, they often warm the emulsion first. One South African data sheet, for example, gives 60 °C for CRS-60. Too much heat boils off water and can ruin the emulsion, so stay inside the limits in our storage and handling guide.

How long should I wait after spraying bitumen emulsion?

There is no fixed time, because it depends on the grade and the weather. Rapid grades can break in minutes on a hot, dry day, while slow grades and cold or wet days take much longer. Watch the color: wait until the emulsion has turned from brown to black and no water shines on the surface. Only then put asphalt on a tack coat. For chip seals, follow your project rules for rolling and opening the road to traffic.

Can I spray bitumen emulsion in the rain?

No. Until the emulsion breaks, rain can wash it off the road. Cationic grades stick well to wet stone, but they still need a dry spell after spraying, so check the forecast first. Many data sheets also set a minimum road temperature. One South African data sheet, for example, asks for at least 10 °C on the road surface.