Deposit on floor tiles

My son has a problem with his kitchen floor tiles. A white deposit keeps re-appearing on one part of the floor as in the image below
https://www.dropbox.com/s/hy709aabxtouc3n/2013-04-21%2015.50.42.jpg
Any ideas as to the problem or cure?
Mike
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On Sun, 28 Apr 2013 07:49:02 +0100, Muddymike wrote:

Looks like damp.
If so, probably no easy cure - it may involve lifting the tiles and redoing the floor.
Cheers
Dave R
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"David.WE.Roberts" wrote in message

It does look like damp, but would damp rise up through glazed tiles like that?
Mike
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They don't look glazed (although it's hard to tell in the picture). They look like quarry tiles, which are somewhat porous.
Can you scrape any of the white stuff off with a blade? I would collect some and see if it dissolves in a drop of vinegar, which would imply it's salts carried up in moisture, and crystalised out as the moisture dries.
Another thought would be that the tiles are on something which is rotting, and it's mold which is coming though, or mold is growing on something which has been spilt and soaked in to the tiles.
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Andrew Gabriel
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