First porosity, and then mechanical testing (if you have the possibility of measuring porosity without dipping in water the sample, for example with gas). If you have to use water (Archimede's principle in water), you can do first the mechanical test, but the pieces of the component broken should be big enough).

Dear Shiv Kr Verma

The best answer to your inquiry is to adopt three samples : the first is to complete the mechanical test, the second to complete the physical test, and the third to complete the physical test followed by the mechanical test. This approach supports the integrity of results and for increasing the reliability and repeatability of the results up to standard level,it is preferable to adopt two sets of samples to become total number of samples six . My best regards .....