This has been hanging around a while... input welcome, though I may be
slow in dealing with it this time
Bitumen is the black solid in tarmac roads.
Its slight flexibility enables roads to handle vibration from traffic,
and enables roofing felts to bend, as long as they're not too cold.
It melts when heated with a torch, at a temperature high enough to
make molten bitumen a definite risk to handle.
Bitumen sticks to almost anything, even polythene, but few things
stick to it once its dry.
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.
Bitumen is an effective glue, and unlike most glues its 100%
waterproof. However there are stronger glues. The slow drying time of
solvent bitumen is an issue, as is its tendency to slowly ooze out of
joints making a mess. Hot bitumen was widely used for parquet floors,
and is still good for the job.
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, but more bitumen will.
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.
=3D=3D=3DRoofing felt, with fibres=3D=3D=3D
Many roofing felts are simply bitumen and fibres. When a small patch
is wanted it can be easier to use bitumen in sovlent & synthetic fibre
cloth than travel out for a new roll of felt.
Bitumen paint has long been used as a DPC in floors & walls. Its also
used for tanking basements etc.
There are 2 types of tarmac, hot lay and cold lay. The difference is
that 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 good solid surface for it to
last, eg hardcore and gravel rolled firm.
Tarmac is much cheaper bought as tarmac than mixing on site. Scalpings
(used road surface), can be had for around =A3200 per 20 ton truck load
Rigid roofing sheets such as corruline and onduline are fibres stuck
together with bitumen.
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
# Roofing felt. Bitumen and fibres, sometimes capped with stone waste
# Roofing sheet. Bitumen and fibres
Where its wanted for something to stick to bitumen, sand is sprinkled
on while its wet. Cement, paints etc then stick to the sand.
=3D=3D=3DRoof repair gloop=3D=3D=3D
Bitumen is used to repair cracks and splits on roofs, both felt roofs
and permanent roofs. The result doesn't last forever, but it has its
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
Petrochemical solvents are used with bitumen. Choice of solvent
affects drying times. From slowest to fastest:
* Diesel - when you want it to stay soft as long as possible
* Paraffin - paint dries out in a couple of days in summer
* heating oil & lamp oil - as paraffin
* White spirit - a much used solvent with bitumen
* Petrol - not safe to use
* Lighter gas - evaporates in seconds, usable for removing small spots
of bitumen, but other solvents are preferable.
Applied with any of the following:
# Blow torch to melt the underside, then apply, pressing it down
# Stick it down with bitumen in solvent
# Nail it
Most better quality roofing felts use modified bitumen, which stays
flexible in cold weather. The longer life of good felts comes
primarily from the synthetic fibre content, whereas cheap felt uses
mixed rag, which contains a high percentage of rottable natural
- posted 10 years ago