Weight
For load calculation purposes use 2.4 kg./m2 per mm. of thickness
for the laid material. Fire
Because of its high mineral content, mastic asphalt is virtually incombustible. Indicative tests have been performed on samples of insulated mastic asphalt roof decks in accordance with procedures specified in (draft) European Standard prEN 1187-1 and prEN 1187-2. No significant flame spread was observed and no flame penetration occurred in either test. Mastic asphalt fulfills all the external fire resistance required for a roof covering and achieved the highest rating (P60) when tested as described in BS 476: Part 3 1975. Thermal Conductivity
Mastic asphalt has a k value of between 0.43 and 1.15 W/m°C and does not significantly contribute to the overall thermal insulation of roofing. A k value of 0.50 W/m°C may be assumed for design purposes. Thermal expansion
Mastic asphalt is thermoplastic and is capable of accommodating normal movements encountered in well-designed building structures. Toxicity
Mastic asphalt is non-toxic and is generally suitable for use in contact with potable water. Resistance to water
Mastic asphalt is impervious to water. Vapour resistivity
The vapour resistivity of mastic asphalt can e assumed to be not less than 100,000 MN s / (g m). For condensation control calculations a factor of 20,000 MN s/ (g m) may be taken (i.e. the ratio of the vapour resistivity of the material to that of still air) see also BS 6229:1982. Resistance to micro-organisms
Mastic asphalt is vermin-proof and rot-proof. Compressive Strength
When mastic asphalt is fully confined it has the same compressive
strength as the containing material. When not confined, the
compressive strength is dependent upon a number of factors including
the temperature to which it may be subjected. Odour
Mastic asphalt is odourless after laying.
