Spreading Salt & Sand Mixture on Snow on Shabbos
According to Maran shlita, on shabbat, would it be permitted to spread a salt and sand mixture in order to melt snow outside one’s house if the floor is made up of cement or is there a חשש of בונה?
This would be permitted.
There are two potential problems with spreading such a mixture on the walk on Shabbos. One would be the melocho of Boneh which you mentioned. In this regard salt poses no problem as it is will dissolve and by it’s nature is only temporary. Sand by it’s nature can remain and therefore there are those who are stringent. The Rav’s opinion is that the sand is permitted as well. It’s presence is clearly temporary and undesirable once the ice is no longer there. See Eruvin 104a, Shulchan Aruch 313:10, and Shmiras Shabbos Khilchisa Chapter 25 footnote 49.
The other issue is that of Molid, the Rabbinic prohibition of changing something from a solid state to a liquid state. However, here the melting is not being done by rushing the snow with his hands, rather it is being caused by the spreading of the salt. While we are generally stringent even for this form of Molid, the Rama in 318:16 writes that in a case of need one may be lenient. This case may also be comparable to what the Gemara describes in Shabbos 42a that when there is a danger in the public domain one may violate the prohibition of muktzeh to remove it, see Rama 308:6. Presumably this would be true of the Rabbinic prohibition of Molid as well.