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9. Breaking an incomplete [non-sturdy] vessel on Shabbos “Mustaki”:
It was already explained that there is no building or destroying [prohibition] by vessels which are not large enough to hold 40 seah and are not sturdy structures. Based on this if an earthenware barrel which does not hold the measurement of 40 seah shattered [before Shabbos] and then had its pieces glued back together with tar, then it is permitted to break this vessel on Shabbos, whether using one’s hand or whether using a vessel, in order to remove its content. [This means that the allowance to break even such an item is only if one is doing so for a Shabbos need, top use its content.]
Why breaking the above vessel is not considered destroying: Doing so does not involve [the] destroying [prohibition] because [the barrel] is no longer [considered] a complete structure [since it broke and has been glued back together].
The prohibition in intending to make an elegant opening for the vessel: [However, this lack of the building prohibition is only] as long as that [upon breaking into the barrel] one does not intend to puncture a nice hole so that it be an elegant [looking] opening for [the barrel], as if one does do so then he has fixed the vessel [on Shabbos] and is liable for [the] “Making a Finishing Touch” [prohibition] as will be explained [in Halacha 17]. However, if one does not intend [upon puncturing the barrel to make a nice hole] then he is allowed [to puncture it]
The reason it is permitted when there is no intent to make an elegant opening: No decree was made against making a hole [even when one does not intend to make an elegant opening] due that one may come to intend to do so, because a barrel which is broken and glued back together with tar is degrading in one’s eyes and one [thus] does not think about making a nice hole in it when he returns [after gluing it back together] and punctures it.
What is the definition of a Shabbos need?
It is only permitted to destroy an un-sturdy structure if one needs to remove something from within the item in order to use that content for Shabbos. For example, if an un-sturdy vessel contains food, one may break through it in order to eat food that is in it. However, to destroy it in order to hide something in it is forbidden even by a non-sturdy structure.
 Admur 314:1; Michaber 314:1; Beitza 33b; Mishneh Shabbos 146a
 Levush; Peri Megadim; Ketzos Hashulchan 119 note 18
 Lit. “Hitting with a hammer.” This refers to any finishing touch that one does to a vessel.
 Admur ibid; Tosafus Shabbos 146a
 Ketzos Hashulchan 119 footnote 18