Why are some hard-facing products limited to two or three layers?

Limited-layer products usually are in the metal carbide families, such as chromium carbide and tungsten carbide. You can apply martensitic and austenitic products in unlimited layers unless the manufacturer specifies otherwise.

The brittle nature of the metal carbides leads to check-cracking, and as multiple layers are applied, stress continues to build, concentrating at the root of the check cracks, until separation or spalling occurs between the parent metal or buffer and the hard-facing deposit.