The skim fraction that is a by- product of centrifuging process, has 3% - 4% rubber content. Such a low percentage plus an increased proportion of non rubber constituents demand that to recover the rubber, a very strong acid be used. Such a recovery using sulphuric acid has its ill effects on the rubber content. This grade, though not technically good, is still very viable economically and is used in non critical applications.
The coagulated rubber is thoroughly washed with water and creped by passing through a battery consisting of coarse rollers and finally smooth rolled. The sheet obtained is dried and is marketed as skim crepe. This rubber is very fast curing and results in hard vulcanisates. The manufacturer can thus save on expensive accelerator dosage.