Monday, September 10, 2012

Ice Jacking

Ice jacking is a phenomena that occurs when water is frozen, water is drawn to the freezing front through the soil, and freezes. There is also lateral frost jacking where water ingresses into a crack and freezes, producing large lateral forces. The amount of movement can  become substantial when partial melting and cyclical freezing occurs.

This can occur in a number of situations. The typical one is in old stucco homes with no insulation and vapour barrier in the joist space over the basement. Water condenses and freezes, expands, and produces lateral force. The sun hit it, it melts, runs down, freezes and expands. You get the picture. Beam pockets over basement have a similar issue. Slabs outside have the same effect happening next to houses.

This week I saw a new occurrence of this, inside a unheated insulated garage. Cars drag in snow and it melts, and condensates on the grade beam. On nice days, this melts, runs down into the space between the grade beam and slab an freezes. This provides force, and in this case, after the slab moved a bit, it pushed the grade beam out of alignment.

The solution is not cheap. Heat, to prevent freezing, is one solution. But just insulation with a vapour barrier may be enough. The thermal gradient and water may be there, but these are separated to a point where the thermal capacity is not sufficient to produce frost in quantity to cause a problem. The vapour barrier must be attached to the concrete to prevent moisture ingress with a mastic or like.   

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