Tiling over old glue

[brettsyoung]

Hi, I'm clearing the tiles from our horrid 50 year old bathroom and preparing to lay new ones. Bugger of a job getting the old ones off, but that's just time and effort. My question is does it matter if much of the old adhesive is left behind before gluing the new tiles down. Everywhere I look it says it needs to be removed but I can't think why, unless the new adhesive doesn't take well to the old. What do you think? Thanks Brett

[aldav]

I'd be getting rid of it. The floor (first pic. ?) looks like all it needs is abrading back to a good surface. The walls will be a bit more work. It looks like some of the adhesive (mortar ?) has come off with the tiles and some has stayed on the wall - that should tell you something. If you don't get all the adhesive off the walls you'll have aa hell of a time if you're intending to use a notched trowel to apply the adhesive.

[TassieRob]

I would be removing it as recommended. The old glue can compromise the adhesion of the new glue. It is a bugger of a job to remove the old adhesive but is better than having to redo the floor later. I found that a random orbital sander with 60 grit paper was a good way to remove the old glue.

[419]

As the house was built in the 1970s you need to check for asbestos risks. If the tiles are laid on cement sheet it is almost certainly asbestos cement. If so, scraping the adhesive off back to the base will release some dangerous asbestos fibres and sanding or grinding will release way, way, way more and be a danger to anyone in the house for some time. It's easier and safer to remove the old sheets and replace them with new current non-asbestos ones, as long as removal is done properly. Asbestos cement sheet can be identified visually with a fair degree of confidence but you need to see the back of the sheet, although there might be some asbestos cement sheets which lack the distinctive pattern. Unless you get it professionally tested, for safety assume that anything built before the 1980s and even well into the 1980s with cement sheet contains asbestos.

This assumes the old tiles were ceramic, which seems to be the case from the pattern in the first picture, but if there were any vinyl tiles then both they and the adhesive could contain asbestos. If so, the adhesive is friable asbestos which is much more dangerous and much harder to remove safely than asbestos cement sheet.

[rwbuild]

BEFORE you re-tile you will have to water proof the floor and walls with one of the proprietary products and ALWAYS put 1 extra coat on than the recommended. It is best to scrap any old residue off. A smooth flat surface is the preferred base.

[wozzzzza]

BEFORE you re-tile you will have to water proof the floor and walls with one of the proprietary products and ALWAYS put 1 extra coat on than the recommended. It is best to scrap any old residue off. A smooth flat surface is the preferred base.

i was going to say that as well, no mention of waterproofing yet, needs to be done.

just get a diamond cup grinder on your angle grinder with appropriate vacuum attachment and grind it flat if its concrete. the diamond wheel will rip off whats left there in no time and leave it in your appropriate vacuum.

aahh, but if its that black gooey gluey softish crap, sharp large scraper and have fun. thats your old waterproofing that needs replacing, then cup grind it afterwards flat.

[brettsyoung]

...

[brettsyoung]

I'd be getting rid of it. The floor (first pic. ?) looks like all it needs is abrading back to a good surface. The walls will be a bit more work. It looks like some of the adhesive (mortar ?) has come off with the tiles and some has stayed on the wall - that should tell you something. If you don't get all the adhesive off the walls you'll have aa hell of a time if you're intending to use a notched trowel to apply the adhesive.

Thanks mate. Was avoiding the inevitable truth!

- - - Updated - - -

I would be removing it as recommended. The old glue can compromise the adhesion of the new glue. It is a bugger of a job to remove the old adhesive but is better than having to redo the floor later. I found that a random orbital sander with 60 grit paper was a good way to remove the old glue.

Thanks mate!

[wood spirit]

Don't know - but logic should say that if it is too hard to scrape off - then it should be a good base for the new glue?