A form of surfacing in which one or more layers of weld metal are deposited (for example, a high alloy weld deposit on steel base metal which is to be welded to a dissimilar base metal). The buttering provides a suitable transition weld deposit for subsequent completion of the butt weld on the groove face of one member.

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Urban Dictionary: Buttering
Buttering | Definition of Buttering at Dictionary.com
Buttering – definition of buttering
butter somebody ? up | meaning of butter somebody ? up in Longman Dictionary of Contemporary English | LDOCE
BUTTERING | definition in the Cambridge English Dictionary