Why should metal be wiped clean before applying mastic

Plain-English answer

You apply a layer of bucket mastic over a newly pre-assembled TDC companion flange joint, but skip wiping down the metal skin, causing the water-based sealer to roll up and slide right off the thick layer of factory stamping oil.

Sealant will not bond to oil, water, or dust. Clean and dry the joint first, then reapply mastic to a mechanically closed seam. The likely recovery is to check the condition, correct prep/setup if it is within your assignment, and bring the foreman clean information before the work creates rework overhead.

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Use this as training guidance. Foreman direction, approved drawings, project specs, manufacturer instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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