Monel is a copper-nickel alloy. The nickel makes the weld pool very sluggish and it doesn't wet in like carbon or stainless steel. One must be very careful to remove all oxides after completing every pass. One must also direct the welding arc exactly where fusion must occur, in other words, care must be exercised to direct the arc into the toes (of the weld bead) to ensure proper fusion if weave beads are used. The width of the weave should be limited to maybe 1 1/2 times the electrode diameter to limit the probability of fusion defects along the toe of the weld bead. Depending on the alloy (how much nickel), it may be necessary to use a rotary file, rather than a stainless steel brush, to remove the tenacious oxides from each weld bead.

Good luck - Al