Frost has been getting in through the mortar then. The white powdery
deposit is efflorescence, or salts from whatever the mortar or the bricks
are made from. It might be a good idea for you to have the house repointed,
but make sure that the builder doesn't change the mortar for a harder or
more dense mixture, as this may cause even more problems not allowing the
bricks to breath properly.
Get a local builder in. If they know the area, then they'll probably know
the older construction methods used around your district.
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