A lot of weekend do-it-yourselfers aren’t sure whether to use putty or caulk on various home projects. It’s really simple if you remember this rule:
Putty is a doughlike compound used to fill in holes (from nails for example) and for surface defects or open spaces.
But, by definition, caulking is quite different. It’s an old shipbuilding procedure of filling the seams between the planks to make a vessel watertight. Today, caulking still means the same. It’s used to prevent water damage on long seams, such as around windows and doors, outside — and around sinks, tubs and showers, inside.
Other uses for caulk include hiding gaps in woodwork and filling long, narrow cracks in ceilings and walls. If it’s a hole or a scratch, use putty to match — but if it’s a long, open seam where water can leak, just lay in a bead of waterproof caulk like silicone.