To cover, coat, or plaster with loam (a type of soil mixture); to apply loam to a surface.
From 'be-' (a prefix meaning to cover or cause to be) plus 'loam' (Old English 'lam,' a mixture of clay and sand). Medieval and early modern English verb formation.
The 'be-' prefix in Old English was incredibly productive—'besmirch,' 'bedazzle,' 'befriend'—it created verbs meaning 'to cause to be or cover with,' and 'beloam' follows that exact pattern.
Complete word intelligence in one call. Free tier — 50 lookups/day.