If the salt absorbs water, why not put a bowl of salt next to the windows on cold and humid days so that it absorbs the humidity from the air and thus prevents it from forming condensation on the glass? This is indeed a “Grandma’s trick” which has been talked about again in recent days with the arrival of winter, perhaps as a home solution to be used in kitchens or bathrooms, the rooms of the house where most water vapor. Unfortunately, however, salt’s ability to absorb atmospheric water vapor is low if not when the relative humidity of the air is very high, then under realistic conditions the “trick” will work little or nothingexcept in small and very humid rooms.
It is true that table salt (mainly composed of sodium chlorideNaCl) is one substance hygroscopicthat is, predisposed to incorporate water molecules into its crystalline structure. However, the hygroscopic action of sodium chloride is very mild as long as the relative humidity of the air does not reach values of 70-75%; only beyond this threshold does the salt begin to absorb water vapor in significant quantities. For comparison, at the temperature of 20°C the ideal air humidity is around 50%condensation on window glass begins to form around 60% and above approximately 70% mold begins to form on the walls.
So salt can have a small effect on reducing air humidity when the latter is very high. However, less humidity does not guarantee the absence of condensationgiven that its formation depends on many other factors, mainly the temperature difference between the inside and outside of the glass, which is the truly crucial parameter.
If you want to avoid the formation of condensation, therefore, the “salt trick” can perhaps provide some benefit as a do-it-yourself solution in a small, steamy bathroom after a hot shower or in a small kitchen where you have cooked for hours, but is far from an optimal solution. The anti-humidity devices on the market, moreover, use substances that are much more hygroscopic than table salt, such as colloidal silica or some calcium salts.
In any case, circulate the air opening windows or installing highly thermally insulating fixtures, perhaps with double or triple glazingis definitely more effective than any bowl of table salt next to the window.
