I bought some new tiles, but dont want to take the old ones off one wall, been told to use pva glue and water and put on top of the old tiles.... does this work? Or do I do that then put tile adhesive on as well as? Dont want to put them on and then have them fall off ....
You'll probably find that tile adhesive will grip well anyway, but if you can scratch the glaze of the old tiles so much the better...an ordital sander with some 80 or 60 grit paper would work well. No need to spend your life doing it though. Watch for bits of glaze flying - unlikely but wear goggles.
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Try fixfault.com to fix general d.i.y.