Calcium chloride is the most aggressive ice melter working down to well below zero and magnesium chloride is very good.
Magnesium chloride on roof.
Organic salts like magnesium chloride are slightly more effective than inorganic salts.
It is not as likely to stain or cause corrosion as sodium chloride but it can damage wooden gutters.
If you use it make sure it s pure magnesium chloride.
Gel melt can be positioned directly on the roof or the ice dam to carve a deep channel into the ice buildup so that melt water has a channel to runoff into the gutter or downspout.
It melts ice faster than sodium chloride does works at lower temperatures than sodium chloride and also melts larger volumes of ice.
Most common high performance ice melters such as magnesium chloride or calcium chloride will certainly melt the ice but they may also cause staining of the shingles and could also cause corrosion of the gutters aluminum siding or fasteners.
Salt will leave a white residue and is very corrosive to unprotected.
Rock salt is sodium chloride cheap and poor.
Calcium chloride is the best salt to use on ice dams according to handyman glenn haege.
Is your roof asphalt shingles.
Also it s the least likely to cause all the damage listed above.
Another draw of magnesium chloride is that it s reasonably safe for your pets and more environmentally friendly.
According to a 2017 review in current nutrition and food science magnesium chloride and other magnesium salts like magnesium aspartate gluconate citrate and lactate have a bioavailability of between 50 and 67.