another type of fcaw uses a shielding gas that must be supplied by an external supply. this is known informally as "dual shield" welding. this type of fcaw was developed primarily for welding structural steels. in fact, since it uses both a flux-cored electrode and an external shielding gas, one might say that it is a combination of gas metal (gmaw) and flux-cored arc welding (fcaw). the most often used shielding gases are either straight carbon dioxide or argon carbon dioxide blends. the most common blend used is 75% argon 25% carbon dioxide. this particular style of fcaw is preferable for welding thicker and out-of-position metals. the slag created by the flux is also easy to remove. the main advantages of this process is that in a closed shop environment, it generally produces welds of better and more consistent mechanical properties, with fewer weld defects than either the smaw or gmaw processes. in practice it also allows a higher production rate, since the operator does not need to stop periodically to fetch a new electrode, as is the case in smaw. however, like gmaw, it cannot be used in a windy environment as the loss of the shielding gas from air flow will produce porosity in the weld.