floor tile adhesive not sticking to back of tile

[cutchi]

I have just done 15sq. metres of ceramic floor tiles and while cleaning them ready for grouting found a couple not stuck down properly. On removing them I found almost no adhesive on the back of the tile.
I am using all Wickes products - ceramic floor tiles, powdered adhesive for ceramic floor tiles, floor and wall tile grout.
I mixed adhesive according to instructions, 1 part water, 3 parts powder, only enough to do 2/3 metre at a time. I have put correct thickness on as coverage worked out exactly as stated and used a floor spreader with rounded notches.
Although no other tiles are loose, I can hear a couple of 'hollow' patches. Don't tell me to take them all up, I'd rather shoot myself!
Am I doing something wrong? The subfloor is concrete, laid about 6 years ago and adhesive is sticking to that OK. The reason I'm asking is that I have another 25 metres to go, some on concrete, some on new self-levelling compound and some on existing quarry tiles.
gcol has already advised me to use porcelain tile adhesive over the quarry tiles (thanks) but why is my adhesive not adhering to the tiles???

 

[jefoss]

check the adhesive bag, it should read for porcelain, if not there is your problem and yes rip it up and start again!

 

[cutchi]

check the adhesive bag, it should read for porcelain, if not there is your problem and yes rip it up and start again!

Why?? I am using ceramic tiles on a cement floor - I know I should use porcelain tile adhesive for them when I come to cover the quarry tiles.
The adhesive is bonding well to the cement (2 hours today to chisel up 2 tiles worth) but not to the back of the ceramic tiles.

 

[gcol]

This is unusual for a powdered adhesive. The only real thing I can suggest is that you mixed the adhesive too dry (should be like smooth peanut butter) or you left it too long after spreading out before sticking the tiles down.

 

[cutchi]

This is unusual for a powdered adhesive. The only real thing I can suggest is that you mixed the adhesive too dry (should be like smooth peanut butter) or you left it too long after spreading out before sticking the tiles down.

Hi gcol, after being on my knees all day chipping up set adhesive, re-laying tiles and grouting good ones, I cleared up all my tiling rubbish and saw that my empty Wickes adhesive bags had a date on them of 16.04.08! As I only bought them last week they have sold me out of date material! Could this be the cause? I mixed according to instructions and used each small mix within 15 minutes of preparation.
Must thank you for your input, you seem to be the only one who takes time and trouble to read the actual problem and give constructive advice

 

[gcol]

I wouldn't have thought that it would have made such a difference being a couple of month out of date. Having said that, I can't be sure and would suggest that it's certainly worth giving Wickes a hard time about it.
It sure sounds like you've gone about laying them correctly as far as install times go, so unless the tiles are teflon coated on the back, then I lay it on thick with Wickes that their old adhesive was the reason for failure. See if you can get a refund and possibly some compensation - then buy some different adhesive.
Sometimes you do get a bit of a glaze on the back of tiles that can reduce adhesion if you leave the adhesive a bit too long. You can generally get around this by applying a thin skim of adhesive directly onto the tile before laying into the adhesive on the floor.
Hope you get sorted.

 

[jefoss]

id have just used porc adhesive anyway, with the way the floor is.

also if wickes tried to sell me any adhesive, id have said to the assistant "look over there" and whilst he was looking, legged it.