Page 70 - DILMUN 14

survival in such an aggressive climate (proimity of the sea; direct cxposition to the

fierce North wind) accounts for thcir soundness and calls for more investigation on
he origial aggregates.

B٨HRAIN FOR'

'Ivo very different groups of mortar are visible in the ruins of Bahrain fort: a
greyish one, that is peculiar to the Portuguese constructions, and a yellowish one
which distinguishes the earlier parts",

ISLAMIC PHASE

A major change in technique seems to take place during the construction of the
Islamic stronghold, i.e. the inner enceinte of Bahrain fort. he mortar belonging to
this phase, in fact, is virtually free of gypsum. "Light yellowish brown in colour",
this highly porous mortar appears on visual examination to contain "pink, orange
yellow, reddish brown particles embedded in carbonated lime matriy', Coal
fragments and shells have also been observed. Moreover, the one sample
chemically examined gave the following composition :

Water soluble salts .32
Silica sand 34.4
Carbonate sand + lime 46.7
Gypsum 4.6

If the binder can be positively ascertained, what may be said about the
aggregates? Notably, there are materials that enable lime mortar to set
hydraulically, i.e. with no need of air. hese materials like certain volcanic ashes,
special kinds of earth or, as in the Roman "cocciopesto', crushed bricks have
widely been used to improve the hardening of the mixes.

ln our case, the colour of the mortar as well as the amount of silica detected
suggest that clay was possibly used to obtain an hydraulic mix. lnteresting enough,
this hypothesis is strengthened by the memory of a lost Bahraini technique :
according to scattered information, a sort of sea clay (tin-al-bahr) collected on the
coral reef was burnt and mixed to lime, resulting in an extremely hard, orange
coloured mortar. If such a technique was used by the builders of the Islamic
stronghbld, it is impossible to say; but the shells found in the samples fit this
possibilityle.

PORUGUESE PHASE
When, in 1561, the Portuguese added their defensive works to the earlier

fortification a new mortar was employed. A clear demarcation line ("coup de

53