Bitumen

Bitumen is the black solid in tarmac roads. It has several uses in DIY, as adhesive, roofing sheet, paint, waterproofer and sealant, mortar, and of course in tarmac.

Properties

Bitumen's slight flexibility enables roads to handle vibration from traffic, and enables roofing felts to bend, as long as they're not too cold.

When heated with a torch it melts, and molten bitumen is normally used at around 200C, making it a definite risk to handle. It can soften to a degree in full sun on the hottest summer days. In midwinter it becomes stiffer still, making unmodified bitumen based roofing felt a problem to work with. This behaviour change over a wide temperature range occurs because bitumen is a mixture of over 200 different chemicals.

Bitumen sticks to almost anything, even polythene, but few things stick to it once its dry.

Emulsified bitumen in water is usually acidic, sometimes strongly so. This adds handling issues and limits its uses. This issue doesn't apply to other bitumen products.

Uses

Sealant

Bitumen is totally waterproof, and sticks to most things. The slow drying time of solvent bitumen can be an issue, and most things won't stick to bitumen unless its blinded with sand.

Glue

Bitumen is an effective glue, and unlike most glues its 100% waterproof. But its not one of the stronger glues. Its liquified with heat or solvent.

Hot bitumen was widely used for parquet floors, and is still good for the job.

The slow drying time of solvent bitumen is an issue, as is its tendency to slowly ooze out of joints until fully set. Bitumen & solvent is also a good candidate for vinyl tiles on damp floor slabs, as its one of very few glues totally unaffected by damp. Slow drying and tendency to creep and ooze while drying are downsides. Bitumen in solvent has very little grab.

Bitumen used as glue can be removed from non-porous surfaces with solvent or heat. When bitumen remains and regluing is wanted, most glues won't stick to it, more bitumen will. Specialist bitumen compatible glue is available, though more bitumen is often just as good.

Paint

Bitumen used as paint isn't prone to peeling off, and it sticks the surface of the substrate together. It lasts extremely well out of the sun, and well in the sun when on a firm porous surface such as masonry. When it has no hard immovable substrate under it it tends to crack & split over time.

The black colour isn't the most popular. Adding red pigment (iron oxide) can make bitumen brown or a very dull red. Iron oxide is sold as red cement colouring powder.

Bitumen emulsion is sometimes used to renovate worn tarmac drives. It wears off after a bit.

Roofing felt, with fibres

Many roofing felts are simply bitumen and fibres. When a small patch is wanted it can be easier to use bitumen in solvent & synthetic fibre cloth than travel out for a new roll of felt. Natural fibres don't last well.

DPC/Tanking

Bitumen paint has long been used as a DPC in floors & walls. Its also used for tanking basements etc.

Tarmac

There are 2 types of tarmac, hot lay and cold lay. Cold lay has added paraffin, diesel or white spirit to soften it, so it doesn't need heating to apply it.

Tarmac must be rolled to compact it, and needs to be laid on a well compacted surface for it to last, eg hardcore and gravel rolled firm. A couple of inches of tarmac laid on soil by a dodgy cowboy can look great at first, but weeds grow through and it soon breaks up.

Tarmac is much cheaper bought as tarmac than mixing on site. Scalpings (used road surface) can be had for around £200 per 20 ton truck load in 2010.

Roof sheet

Rigid roofing sheets such as corruline and onduline are fibres stuck together with bitumen.

Paving Mortar

Bitumen is sometimes used as mortar between paving setts or slabs. Its poured in and resists weed growth & cracking. Its strongly contrasting appearance with most paving and higher cost than cement mortar limits its popularity.

Damp treatment

Bitumen paint is sometimes used as a remedy for damp. It is waterproof, but painting the outside of historic houses with it can make damp worse by preventing evaporation. Painting the interior of basements and retaining walls produces a dry interior surface, but increases the water content within the wall, which can occasionally lead to joist rot.

Asphalt

Asphalt is a mix of bitumen and clay, sometimes with added colourant, usually iron oxide. Its laid and polished. The result is a very tough hardwearing long lasting floor with some antibacterial properties.

Timber treatment

Bitumen is sometimes used to delay rotting of timber by waterproofing it. A classic example is bitumen coating the bottom section of fenceposts to keep them from touching the wet soil. Coating the foot or so from ground level down delays rot, further down the wood is less rot prone.

Psoriasis

Coal tar has long been used to treat psoriasis, and is very effective. Concerns about its safety have led to bitumen being used in its place. The resulting appearance discourages most people from using it this way, despite its effectiveness.

Paper roof

The paper roof is a historic curiosity that was once a standard roof type in some parts of the country. It was made of layers of bitumen coated paper, and damage was often repaired with a household iron. Its a predecessor of modern roofing felt.

Forms

Bitumen comes in various forms

Just bitumen. Heat to melt it and apply.
Bitumen in solvent. Pour/brush on and let dry
Bitumen emulsion. Emulsified in water
Roof repair gloop. Bitumen with fibres & solvent
Tarmac. Bitumen with stone & chalk/clay. Cold lay also contains a little solvent.
Roofing felt. Bitumen and fibres, capped with sand or stone waste
Roofing sheet. Bitumen and fibres

Techniques

Blinding

Where its wanted for something to stick to bitumen, sand is sprinkled on while its wet. Cement, paints etc can then stick to the sand.

Roof repair gloop

Bitumen is used to repair cracks and splits on roofs, both felt roofs and permanent roofs. The result doesn't last long term, but it has its uses.

Mixing chopped fibres into bitumen enables it to last better on a roof. The fibres reduce its tendency to crack. Synthetic fibres last much better than rottable natural fibres, and glass fibre lasts even better.

Solvents

Petrochemical solvents are used with bitumen. Choice of solvent affects drying times. From slowest to fastest:

Diesel - very slow
Paraffin - paint dries out in a couple of days in summer
heating oil & lamp oil - as paraffin
White spirit - relatively quick
Petrol - not safe to use
Lighter gas - evaporates in seconds, usable for removing small spots of bitumen, but other solvents are preferable.

Roofing felt

Applied with any of the following:

Blow torch to melt the underside, then apply it, pressing it down
Stick it down with bitumen in solvent
Clout nails

Most better quality roofing felts use modified bitumen, which stays flexible in cold weather. The longer life of good and mid-quality felts comes primarily from the synthetic fibre content, whereas cheap felt uses mixed rag, which contains a high percentage of rottable natural fibres. The best felt uses glass fibre.

Tarred roof

The tarred roof is the ancestor of roofing felt.

Boiling

When hot bitumen's wanted, its usually heated to at least 200C in a bucket on a gas ring. The high temperature plus its sticky nature makes it a serious burn risk, requiring protective clothing.

Torching

Playing a torch flame on the surface of bitumen to melt it makes it stick. This is a common technique used with roofing felt.

Fibre reinforcing

Fibres are often added to make the bitumen tougher. Roofing felt and rigid sheets are the prime use for this approach, but fibre can also be added to painted bitumen to reduce its tendency to crack. Fibres can be mixed into the paint can, or sprinkled on the painted surface then over painted.

Filling

Bitumen can be filled with low cost powders such as chalk & clay to reduce cost. Many bitumen products already contain fillers.

Terminology

Bitumen: the black solid fraction of crude oil that fails to boil at 400C

Tar: similar to bitumen, but made from coal. Not generally used now

Tarmac: nowadays this is stone, bitumen and clay or chalk. Tarmac was once made with tar rather than bitumen, they look the same.

Asphalt: Pronounced ass fault or ash felt, this is a mixture of bitumen and clay often used for flooring in large buildings

US Terminology

The differences in US terminology can cause confusion on the internet

What we call bitumen, the US calls asphalt.
What we call tarmac, the US calls pavement or asphaltic concrete, so road surface is sometimes called pavement.