Just a note:
Filler classification vs Electrode classification
Electrode classification for GMAW ie. ER70S-6
Electrode classification for GTAW ie. EWP (pure tungsten-green), EWTh-1 (0.8-1.2% thorium-yellow), EWTh-2 (1.7-2.2% thorium-red)...etc...etc...
I agree with Lar on the use and practicality of ER70S-6 for GTAW but it is acting as a filler in this process not the electrode as with GMAW, so you have to be careful regarding the classification of the
electrode if spelled out on a WPS or whatnot.