Another try - Laying vinyl tiles

I've offered to re-tile my elderly neighbours's kitchen and I have a few questions.
She doesn't want the original vinyl tiles removing (they are stuck like hell to a concrete floor anyway) and wants me to tile over them - the only problem is that whoever laid them left gaps between each tile.
What should I fill these gaps with before tiling?
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Not strictly conventional, but we filled missing bits of 1950s vinyl tile and damage to the concrete floor with a cheap brand of interior/exterior filler, sanded smooth and laid the new tiles on top.
It's not perfect, but it was never going to be without starting from scratch. It's not half bad though, and two years so far and it's as good as new.
Before & after at:
http://gillhesk.tripod.com/sitebuildercontent/sitebuilderpictures/030131.floor.jpg
http://gillhesk.tripod.com/sitebuildercontent/sitebuilderpictures/newfloor.jpg
HTH
--
Gill



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Ben wrote:

    If you lay the new tiles at 45degrees to the old ones, you probably won't need to.
    Regards     Capitol
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