tiling over old tile adhesive?

[Olz]

PVA just dries into a thin skin, and its ok at sticking pasta to coloured sheets of paper but that's about it. Think about when you get it on your hands, to get it off you just let it dry and easily peel it off.

Do you really want something so easy to peel off your hand to be the only thing holding adhesive, and therefore the tiles to the wall?




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[Martino]

But then why do plasterers use it on a ceiling?...its the same principle? it dries thin and its the only thing holding the plaster up?

 

[White Room]

Plaster weighs about 2 kg m2...

 

[steve6710]

p.v.a. is used for plastering as it theoretically should never get wet again to the degree tiles in a bathroom or kitchen may. if you paint pva onto pretty much any surface and let it dry for a day, a week, a month or a year it will seem fine untill you wet it. it then turns back to the sticky liquid you started with. plasterers like myself use pva which is the accepted practice but what happens when you have a rising damp problem or a roof or window leak?..... your plaster loses it bond 9 out of 10 .
as another example i am a fisherman who uses pva bags to fill with bait which i attach to the hook, when in the water the pva dissolves and only the bait is left for the fish.
a couple of tests you can do to see the values of pva are: pva a hard surface 6 square inch let it dry - you can sand wood with it
va a hard surface - leave it a day to dry - wet it and touch it- sticky again!slip slide!
sbr is for tiling primer or external plasterwork(render) as it is a latex skin which can handle getting wet again - pva aint bad in the right application if it was for tony hart and morph or blue blue peter it wouldnt be sold at builders merchants i would guess!

 

[steve6710]

sorry to add to previous thread, apply basic sand to the wet pva and allow to dry to make sand paper for the first test i mentioned