I'm not buying this "Vulgar Latin" etymology, and neither is my man Corominas: "Se citan las formas sparadrapum y spadrapor, pero son reflejos tardíos de las formas romances." In other words, it's a mediaeval Latinisation of the Italian word cited above.

Here's the basic problem with it: We have the 15th-century Italian form sparadrappo. If this comes from sparadrapum, then what's the origin of the geminate p? The expected outcome of Vulgar Latin sparadrapum would be *sparadrapo (or *esparadrabo in Spanish), but that's not what we find.