Rationale

In the process of developing a ballot item for a change to the current C191 standard, it was discovered that the current P&B statement is based on an old method for determining final set of paste. Current language for determination of “final set” for Procedure/Method A (which is manual method) was changed a number of years ago and the P&B statement was not updated. The previous language stated that “final set is achieved when no appreciable mark is observed,” and that is what the current P&B for final set is based on. This procedure very subjective and the new language that was approved, improved on the method based on some round robin work and data we also received from CCRL. The current language in C191 states; Determine the Vicat final time of setting end point to be the first penetration measurement that does not mark the specimen surface with a complete circular impression. Verify final set by performing two additional penetration measurements on different areas of the specimen surface. Obtain verification measurements within 90 s of the first “final set” measurement. So, the intent of the committee is to use the current data we have obtained from CCRL to update the P&B statement for final set. The method for determining initial set did not change and does not need to be updated.