WHETHER GAYATRI JAPAM HAS TO BE PERFORMED BY COVERING BOTH HANDS WITH VASTRAM?

While performing gAyatrI japam, one has to cover both hands with vastram.

 strIpumsAtmaka gAyatrIm vastreNAcchAdyaiva japet !
udaye prAnmukhastishthan sankhyAyaiva japet budhah !
asankhyayA apavitrasca japo nishphalatAmiyAt
--- vrddhyamah

OmkArah purushah proktah gAyatrI sundarI tathA !
tayossamyogakale tu karamAcchAdayet budhah !!
---- viSvAmitrakalpa