Tiles Coming Off Screed Re-tiling Advice

[Joss]

About 25sqm. 23 now since two were not tiled on gypsum

 

[Andy Allen]

Not to bad then...if that's possible..lol
At least it's not 100's of meters.
If its any consultation your not the first to experience these problems and you won't be the last !!

 

[CJ]

Lift tiles, park backside in the garden with a grinder, and concrete grinding disk. It will be a horrible job, but you should be able to save them for re-use.

 

[Joss]

@CJ thanks for the advice, a hell of a week end ahead... I'll prog start with a chissel on a well levelled floor to get the most off first.
@Andy... well I'd rather not me not everyone have these issues

 

[peteablard]

I find the best way to remove adhesive from tiles is to cut through the adhesive with a grinder 20mm apart in both directions then the small squares pop off easily with a chisel. It should be the tiler doing it though!

 

[Old Mod]

Well I will push this way. But although as a professional I should know about that.

???? Professional?

 

[Old Mod]

he was not passed the information about the cement type from the main contractor.

As a professional tiler, it should be the first or second question he should ASK!

 

[Stef]

Any tiler worth his salt should know what he was looking at.
I wouldn't be laying a tile on that till the screed is sanded & especially tested for moisture.

 

[Lee@emctiles]

Joss, didnt you tell the tile shop you purchased the tiles from what screed it was?

IMHO the wrong adhesive has been used, and its not been primed or had the laitance removed.

Anhydrite/Calcium Sulphate Screeds:

Anhydrite/Calcium Sulphate Screeds must be confirmed dry via consistent moisture readings across the area to be tiled. Anhydrite/Calcium Sulphate Screeds must be below 85% Relative humidity before tiling can commence. As a guide for drying times of Anhydrite/Calcium Sulphate Screeds, allow 1 day per mm up to an overall depth of 40mm and allow 2 days per mm for anything above 40mm. Anhydrite/Calcium Sulphate Screeds often dry with laitance (a shiny, hard crust) on the surface. The laitance must be removed before tiling commences by mechanically sanding and/or abrading the surface of the screed. Once the laitance has been removed, the screed should be vacuumed to remove all loose dust, dirt and contaminants then primed.

 

[CJ]

Local company that supply pumped screeds in my area told me that the newer Anhydrate screeds don't need mechanically sanding.......just swept, hoovered, and primed as per instructions.

Never had any problems.

 

[dave l and l]

had the screed dropped as well

 

[Andy Allen]

The op says it dropped by half a mill I assume that's the layer of laitance coming off with the tile adhesive ..

 

[Joss]

Yes it dropped by a bit in some areas (though I've only taken one tile away).
@Andy Allen , reading through i'm not sure it's laitance. It looks like dust so my guess is that its either adesive that has chemically reacted or dust which can some up during the drying process (Gypsum concrete - Wikipedia, the free encyclopedia: The purpose of the polyvinyl alcohol is to prevent the surface of the concrete from becoming dusty. While the exact mechanism is not known, it is thought that as the concrete sets, water migrates to the surface, bringing with it fine, dusty particles. When the water evaporates, the dusty particles are deposited on the surface. It is thought that the polyvinyl alcohol prevents the dusty particles from migrating upwards with the water.[3])

 

[Joss]

@Lee@TileTown, I can't remember if I did or not, what would you recmmend for tiling on gypsum? Some users seems to indicate @Bri that just priming isn't enough (I did a couple of sample tiles on a primed area, one stuck with GBTA and one stuck with flexible cement based, then left them for 3 days. The GBTA needed a hammer and chisel to get it up and the cement based needed a wallpaper scraper! So yes some manufactures claim cement based can be used but for me, no way I'll take the risk)

One more question, from experience, would you expect Gyvlon screed to bee so weak to abrasion (I din't put much force and this a small scrapper): Broken Link Removed

 

[Ajax123]

Gypcrete and anhydrite screed are very different things.

There are no new gyvlon screeds and all screeds including sanbd and cement as well as anhydrite shoulkd be mechanically abraded before applying bonded floor coverings eg tiling

None of the anhydrite screeds in the UK market contain polyvinyl alcohol as far as I know

Cement adhesives should be avoided if possible and if they cannot be avoided then a suitably robust primer/sealer must be used

Laitance is only microns thick not milimeters. If you have a skin on the screed that is thick then it's not laitance it's defective surface. This needs dealing with usually by scraping back to good screed.

All screeds should be clean, dry, sound and free from contamination likely to affect the adhesion of floor coveringfs. This is from the British standard

A very high percentage e.g 90 plus... Of floor failures are down to moisture ... Make sure you test it before you tile it. A good proportion of these are exacerbated by poor prep.