If one has wounds on one's face and arms can one do Tayamum?

Respected Mufti, It is stated in Nur al-Idaah that if half or more of the body is wounded then one may perform Tayamum instead of wudu (p.48). (in wudu , the 4 limbs which are compulsory will have to be taken into consideration And in ghusl the entire body has to be taken into consideration).The question which I have is that what if the wounded parts are the arms and/or the face, how can one then do Tayamum ? Because in order to do so one will have to rub sand/ earth onto one's wounds. Please could u enlighten me with the correct ruling.