The buildup is a surfacing variation in which surfacing material is deposited to achieve required dimensions.
The term buildup denotes the addition of weld metal to a base metal surface, the edge of a joint, or previously deposited weld metal for the restoration of the component to the required dimensions. In this case, the strength of the weld metal is a necessary consideration in the component design.

The Buttering is a surfacing variation used to deposit surfacing metal on one or more surfaces to provide compatible weld metal for the subsequent completion of the weld. Buttering differs from buildup in that it is used for metallurgical reasons like PWHT deduction, lamellar tearing prevention, reheat cracking prevention or dissimilar welding, not dimensional control.

Example 1: Buttering is the depositing of a high-nickel alloy onto an alloy steel that requires heat treatment and that later will be welded to a steel that does not require heat treatment. The buttered member (workpiece) can be heat-treated and then joined to the other workpiece with no subsequent heat treatment.

Example 2: Buttering the surface of the susceptible plate with a low strength weld metal to avoid lamellar tearing or cracking susceptibility.

Example 3: Buttering to weld dissimilar material by Nikel-Iron Electrode

Nickel-Iron Electrodes. Welds made with nickel-iron alloys are stronger and more ductile than welds made with essentially pure nickel. The strength properties of the nickel-iron electrode make it suitable for welding ductile irons and high-strength gray irons. This type of electrode is also used for dissimilar joints, such as cast iron containing chromium welded to carbon steel, stainless steel, or nickel-base alloys. Some chromium-containing alloys may require preparation of the joint by the use of a buttering technique before making the weld. Buttering (at Carbon steel side) is used to avoid the formation of chromium-carbides.

Example 4: In-situ Buttering? What is this? See In-situ Buttering welding