Problematic Anhyrdrite floor!

[Perfect Tiling]

Hi there. I have recently tiled a couple of floors in a new house and they have started to come loose. The floor is called hemihydrite which is a new type of anhydrite that does not produce a latent skin so does not need sanded prior to tiling etc (thats what the spec sheet says). The floor with UFH was laid in mid sep at 75mm depth and heating was on for 3 weeks prior to me tiling. Prepared as per the book, with 2 coats of APD primer and used SPF adhesive. A carpenter on site did a moisture check prior to him laying an oak floor and said it was fine. Tiles were laid 2 weeks ago and up until last fri were solid, however today they are loose in places with grout cracks. Other floors have been laid with travertine in the same way and are still solid. The only thing different is the customer has put the heating up to 20 degrees since then and the floor was warm. On lifting a tile it came up with some adhesive on it and the remaining adhesive came up with the primer on it. I think the floor still has moisture in it and this has been trapped under the tiles and caused them to lift due to the heating being put on too much too soon...any ideas. If this is the cause...who is to blame. Customer says he was told by screed installer that floor takes 75 days to dry...however I called the company today who said 120 days...depending on conditions...cold and wet up ere. Many thanks in advance.

 

[Colour Republic]

heating should not have been on after the tiles had laid for 28 days

 

[Ajax123]

Hemihydrate is not a new type off anhydrite. It is alpha hemihydrate ... It is a different chemical arrangement and is by no means new having been around for decades. From your point of view it should be treated exactly the same as anhydrite screed.

All gypsum screeds, and for that matter all screeds, should be sanded in order to prep them for tiles. This is to remove any loose debris or extraneous surface contamination.

Drying time is 1mm per day for the first 40mm depth and 2days per mm there over so approx 120 days. This depends on site conditions as it is based on 20degrees c and 60% rh. Underfloor heating should be comissioned and run up to temperature and then down again before moisture testing. Electronic moisture meters should not be used on these screeds except as an indicator. The correct method is the floor hygrometer or carbide bomb test.

My suspicion is moisture rising to the surface following increasing the temperature. Electronic meters tend oly to measure the top part of the screed so if there was moisture within the body of the screed it might not have been detected.

Underfloor heating should not be applied to a tiled floor for a minimum of 28days following tiling.


apart from that everything is ok....

 

[Perfect Tiling]

Thanks Ajax...thats what I thought. As mentioned I didn't sand the floor as screed company said not to...I did try to sand and scrape a part but nothing came off...no dust...nowt. If moisture is the cause who is to blame? I don't do a bomb test and relied on dates given by customer and screed company who now say 120 days not 75 as previously. I told customer not to put up heating but he did so just my word against his. The heating to the travertine floors has been physically shut off for now so that if moisture levels are too high the floor can still breathe and hopefully be ok. Failed floors are porcelain. This type of screed obviously has some benefits...but not as regards tiling onto!!!!

 

[bugs183]

No one knows these screeds like Ajax, Perfect. He'll sort you out.

 

[Ajax123]

Thanks Ajax...thats what I thought. As mentioned I didn't sand the floor as screed company said not to...I did try to sand and scrape a part but nothing came off...no dust...nowt. If moisture is the cause who is to blame? I don't do a bomb test and relied on dates given by customer and screed company who now say 120 days not 75 as previously. I told customer not to put up heating but he did so just my word against his. The heating to the travertine floors has been physically shut off for now so that if moisture levels are too high the floor can still breathe and hopefully be ok. Failed floors are porcelain. This type of screed obviously has some benefits...but not as regards tiling onto!!!!

it should not really be 75mm deep. That is an error in my opinion as it n needs to be 50mm n underfloor heating or even 40mm with some systems. That would have lopped off a good 50days from the drying time.

now then who is at fault... Well if you have asked if the floor is dry enough and been told categorically yes then you cannot really be held to account. I pf you had been told it was wet and carried on regardless you would be negligent. If you have carried out the tiling without any sort of test or info (which from your original post you have not) then you would probably have a negligence case to answer.moistrue testing is the responsibility of the man contractor normally. Certainly material selection are not at fault as the APD is fine. In terms of sanding this does 2things. 1removes dirt and loose debris and 2 helps to produce a key for the primer to key to. Not sure what sort of project or contract it is though so cannot really predict lines of resposnibility.

 

[Perfect Tiling]

Thanks again Ajax. A moisture ckeck was done by a carpenter prior to laying an oak floor but probably not a true reading. This will probably be a case of everyone blaming someone else. I thought I had done everything as informed. I could have just left it and not said anything but was being honest as I knew it would just get worse as time went on. Forgot to say earlier...the screed seemed soft to me as I could dig into it with a screwdriver and rather than coming out as lumps it was just like grains of sand. The rep from BAL said that if there was a skin the primer would likely have this stuck to it when lifted but it was clean. He thought moisture being trapped by the heating being put on too soon was probably to blame seeing that the travertine is still solid and had to be taken off with a hammer...in pieces (I removed a cutting of travertine that had been down for a week).

 

[Ajax123]

Soft screed suggests that it was segregated which would generally be a result of excessive water addition either at batching or on site. This causes the screedmtomsegregate such that you get a lot of chalky power at the surface with the harder screed underneath. It is usually in patches. Something else that can cause it to be soft is if there has been insufficient reaction due perhaps to freezing but in September this is improbable even in Scotland. This is not really skin as that is a separate sort of entity. Lack of sanding will certainly lead to poor penetration of the primer though.

 

[Perfect Tiling]

Crikey...you know your stuff. The first coat of primer was 1:1 mixed with clean water and was like coating to paper as it soaked right in and didn't puddle at all. Second coat was put on neat at 90 degrees to first. I tried scraping the primer today to see if it came off as a skin but it didn't.

 

[Mark S]

Hi sorry to hear the tiles are lifting,
Not sure whose screed was laid, but at Gyvlon we always recommend the screed is lightly abraided/sanded before the primer is applied. The fact the wood floor is fine would indicate the floor may well be dry.
At 75mm thick the screed is in our opinion 20mm too thick, the optimum thickness with UFH is generally 50-55mm.
As the tile you lifted had primer on the back it would suggest the primer has not penetrated the screed surface, Before commencing any re installation test the floor for moisture using a hygrometer box, or carbide bomb test, nothing else is accurate on anhydrite screeds. The moisture level does need checking.
There are some adhesives on the market that do not require priming, Kerakoll H40 Ideal is one.
hope this helps

 

[Perfect Tiling]

Ajax...forgot to ask. Can this problem not be related to thermal shock due to the heating being turned on too high and too soon. The tiles under the toilet etc where there are no pipes are solid and a perimeter tile has cracked but is still sounding solid. Put this with the fact that the travertine tiles in the rest of the house are solid, leads back to the only tiles going loose are those that have had heat introduced. Floors were fine on Fri last week (I was on my knees siliconing) and thermostats were down at 10 and not calling for heat, today 5 days later they are at 20 with water going throught the manifold at around 45 degreesC. Customer moved in at the weekend so must have turned it up.

 

[Perfect Tiling]

Hi Mark. Thanks for the info. The wood floor is not stuck to the screed, it is an engineered oak floating floor. The tile I lifted was hard to get up and broke into 3 pieces the first part leaving the adhesive on the screed rather than on the tile. The tile had adhesive on it level with the high part of the pattern. Never doing screeds again...not worth the worry...hardibacker or wedi boards all the way!!!

 

[Perfect Tiling]

Mark. If company literature says not to sand then is this a get out clause for me if this is the problem????

 

[Ajax123]

Ajax...forgot to ask. Can this problem not be related to thermal shock due to the heating being turned on too high and too soon. The tiles under the toilet etc where there are no pipes are solid and a perimeter tile has cracked but is still sounding solid. Put this with the fact that the travertine tiles in the rest of the house are solid, leads back to the only tiles going loose are those that have had heat introduced. Floors were fine on Fri last week (I was on my knees siliconing) and thermostats were down at 10 and not calling for heat, today 5 days later they are at 20 with water going throught the manifold at around 45 degreesC. Customer moved in at the weekend so must have turned it up.

yes this is certainly a possibility. The timescales would suggest moisture. Thermal shock could easily be contributory. It s difficulties diagnose at a distance obviously.

Is the trav heated?

 

[Ajax123]

Mark. If company literature says not to sand then is this a get out clause for me if this is the problem????

Yes it would be a you have followed manufacturers guidelines. It does depend on wording though.