The present invention teaches that a tightly woven, and strong layer of fiberglass may be coated or impregnated with sodium silicate in order to produce a strong and fire resistant jamb/frame. The present invention further teaches that a fire doorjamb core may be mass produced from fire resistant layers and the frame core rated for fire safety by a rating agency, thus allowing builders and door manufacturers to produce building structures and doors using that core without individually certifying each model of door or structure. The present invention further teaches a structure/method of mounting for door frames which closely parallels mounting of normal door frames, without special brackets or plates.