Help! Tiles coming unstuck VERY easily!

In the thread "Is it OK to Tile and Grout the same day", I was concerned about the way in which a 'professional' tiler was going to do a job for me. I'm suspicious enough now that he's not getting the job. Since other tilers I've phoned can't do the job for weeks, I'm considering doing it myself.
I've tiled part of my kitchen before myself and it seems ok 4 years on, but this job is to tile round a bath and shower area, which I'm not sure I'm up for.
As a small test, I tiled onto a spare bit of WBP (as is round the bath area) to see if I can do the job acceptably. I used Unibond Waterproof Tile Adhesive. (I didn't grout it.)
After about 48 hours I tried to force a screwdriver underneath a tile, and it came off whole with virtually no effort, leaving the adhesive on the WBP. This area hadn't been primed with PVA. On another area which HAD been primed, the tile still came off intact.
I'm now confused - in John Schmitt's Tiling FAQ he says
"Sand/cement fixed tiles can be "pinged off" intact, tiles correctly fixed with modern adhesive will not come off in pieces bigger than 1"sq. "
So how come mine came off so easily? Do they need a lot longer to really set?
I'm also bearing in mind the comment by The Natural Philosopher in the above thread that
"It needs the merest dab of adhesive to keep it from falling down - all the vertical load is taken by the grout."
Am I too concerned, or am I just rubbish at putting a tile onto a bit of adhesive!?
Finally, is there any particular brand of waterproof tile adhesive that is highly recommended?
Any help much appreciated, and sorry this post is so long!
Eno
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Eno Case wrote:

[snip] Tiling on wood is a tricker than on a surface that disperses like plaster the water in ready mixed adhesive. Was the adhesive on the tiles you removed fully dry? Is that the Unibond stuff they sell in B&Q? If so forget it, you may as well tile with toothpaste. Go to proper tile outlet and get Mapei P25 or similar. Again see Just Tiles tiling guide.
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I am far from an expert on this but I did our bathroom over 2 years ago (my 1st ever tiling job) and they're all still there and solid as a rock! And that was using unibond. I brushed the surface first then PVA'd it. Let that dry for about 8 hours (I think maybe it should be left longer?) and then was very generous with the unibond. I also left it about 2 days before grouting. Not a single tile moved - even the ones underneath a door recess. ie facing vertically downwards. Since then I've drilled the tiles for mounting various bathroom bits and no problem with it. All I can think of is that maybe you need a more generous coating (I coated wall and tile over entire surface not just 5 blobs) and I jiggled each tile quite firmly into place. hth
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dave wrote:

It could be that adhesive is ok for its intended purpose (holding tiles on walls) but won't like being prised off with a screwdriver ... Also your tiles were not on wood presumably?
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True and yes. But there does seem to be a large difference in results. The stuff I used was setting in minutes - if fact too quickly for my liking at the time - and the suction effect alone was considerable. btw I don't have shares in B&Q or unibond or anything :-)
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BillR wrote in message ...

IME tiles are difficult to move by hand after a couple of minutes because of suction. If that isn't the case I'd say the surface is too absorbent.
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Eno Case wrote:

Well if it was the tile to cement joint that failed, whatever you did to the wall was irrelevant.
I have often used Unibond - not the greatest. I usually crack teh tiles taking em off.
Maybe the cement had not dried fully - if you PVA'ed the wall there would be nowhere for the moisture to get out easily.

I suspecty so, yes/

Dunno. What you HAVE proved is that a really weak joint still didn;t result in tiles falling off - you need that screwdriver to lever em up.
After having seen builders building houses, I am of the firm opinion that most houses are not glued, screwed, cemented or nailed togeher. They are juts a pile of building materials laid on top of each other and held together by weight mainly. :-)
If you want a real strong tiled wall, use car body filler in the '5 dab' pattern...never had one of those fall down yet :-)

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