Coal tar is a thick, dark, strong-smelling liquid produced as a by-product of heating coal without oxygen — historically in gasworks and coking plants. In construction it was long used as a cheap water- and rot-resistant binder. Coal tar is not the same as bitumen: bitumen comes from crude oil, coal tar from coal.
Historic uses in construction
- Roofing — tar paper and tar-bound felt, the forerunner of bituminous roofing membranes.
- Road building — tar-bound asphalt, widely used until the second half of the twentieth century.
- Timber preservation — creosote, a distillate of coal tar, for sleepers, fence posts, revetments and poles.
- Damp protection — coating foundations, basement walls and the tops of timber piles.
- Marine and hydraulic work — caulking and tarring timber sheet piling and jetties.
Why it disappeared
Coal tar contains a high proportion of PAHs (polycyclic aromatic hydrocarbons). Several of them, including benzo(a)pyrene, are carcinogenic. Its use in the European Union is therefore heavily restricted:
- Tar-bound asphalt may not be recycled into new asphalt; it is sent for thermal treatment, which destroys the PAHs.
- Creosote-treated timber may not be supplied to consumers in the EU; use is limited to certain professional applications.
- In building work, tar as a binder has been almost entirely replaced by bitumen, polymer membranes and modern wood preservatives.
Recognising it during demolition and renovation
If you meet dark, glossy material with a strong, distinctive tar smell during alterations, assume it may be tar-bound. This mostly arises in:
- old roof build-ups beneath later bitumen layers;
- old asphalt surfacing on yards and driveways;
- railway sleepers reused in gardens (very common as edging — and exactly where you do not want them);
- basement and foundation coatings in pre-war buildings.
Practical rules:
- Do not sand, grind or burn it — that releases PAHs as dust or vapour.
- Have it sampled — a laboratory can determine the PAH content, which decides how it must be disposed of.
- Dispose of it separately — tar-bound material is not ordinary construction waste; waste handlers run a separate stream for it.
- Protection — gloves, respiratory protection and work clothing kept apart from other laundry. Tar also causes skin photosensitivity.
Related terms
- Bitumen
- Creosoting
- Asphalt
- Roof covering
- Emissions
- Ground investigation
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