It depends what kind of crack it was. If the crack was horizontal, then the halacha is just like I wrote in the last Teshuva. If there is a Reviit of water underneath then it was fine. However, if it was a vertical crack. If it seemed like the cup was going to fall apart then you couldn’t use it. If not then if water couldn’t come into the cup, then it was fine. As long as it was glued well then it was OK just the owner of the restaurant should change it because of making Mitzvot nicer.
Explanation:
The Bach (159) is of the opinion that a crack is worse than a hole and if the crack leaks the cup cannot be used.
The Chaye Adam explains (37:7) since a crack will eventually widen and ruin the cup unlike a hole which won’t get bigger.
It seems from the Chaye Adam there is no difference by a crack whether it is Kones Mashkeh or Motzi Mashkeh, we are worried the crack can widen at any time and ruin the cup. For the Bach himself one could think only if the crack is leaking, it is a problem but if it isn’t, then we don’t have to worry about it. So understood the Shulchan Aruch HaRav.
According to the Shulchan Aruch HaRav we are only concerned the crack will widen if it’s already leaking.
The Taz argues on the Bach and says there is no difference between a crack or a hole and there is no need to be stringent.
It seems everyone agrees that only if the crack is leaking then the Bach and Shulchan Aruch HaRav are stringent and the Taz said it is permitted to use.
If we see the crack is widening then of course the cup is forbidden to use.
The Shulchan Aruch Ohr Hachaim 586:8-9 can qualify this further: A shofar which is cracked along is length is worse than a Shofar cracked around is diameter. A Shofar which is cracked along its length we are worried maybe the crack will widen and there will not be proper length of a shofar to low, but if the crack is around it even if it widens and piece of the Shofar falls off if there is still a piece by his mouth and shiur to blow it is fine.
We should be able to apply this by our case as well by the Netillat Yadayim cup, if it is cracked horizontally then if there is a shiur left it is fine but if the crack is to the length then it could widen and the cup will be ruined. So writes R’ Mordechai Gifter.
In regards to glue.
The Shulchan Aruch there by shofar bring an argument whether glue helps by a cracked Shofar. The Mishna Berura explains the question over there is where the glue is considered part of the Shofar or something else which is Passul to blow from.
That is an argument by Shofar but a cup it makes no difference what material it is made out of just will it fall apart. Therefore, if the glue will stop the crack from widening then it will be fine to use the cup.
The Shulchan Tohar does say that R’ Elimelech MiLizhinsk were careful to use a whole cup for netillat yadayim to make the mitzvah more beautiful.
