Using gypsum based adhesive..

[DHTiling]

maybe Alan jackson can shed some light on this....

600 x 600, 600 x 300 and 300 x 300 Brazilian Black slate floor tiles laid with Nicobond Gypfix
adhesive onto a Bardon High Flow calcium sulfate pumped screed with underfloor heating
were reported to be hollow on corners. Screed had been tested and found to be dry before
tiling and brushed and primed with an acrylic primer.
Corner hollowness was confirmed on the larger sized tiles. Where bedding was exposed
following removal of a hollow tile earlier, adhesive residue to the screed was hard, dry and
well adhered. Another 600 x 600 hollow tile still in position was re-lifted. Exposed adhesive
was darker in colour and gave moderately damp readings when tested with a Tramex
moisture meter. The adhesive was not as hard as previously found, especially near the
centre of the tile. A further still installed tile was then removed. Adhesive was both damp
and soft. Tramex reading was High confirming the dampness.
It was concluded from a detailed record of dates and actions that the screed was dry on tile
installation. Moisture from the original application of adhesive had probably been absorbed
into the dry unheated screed sufficient to allow setting and hardening. However when
heating was switched on, no matter how gradually, this moisture was driven back up into the
adhesive, causing it to soften or revert and loose adhesion. The impervious nature of the tile
and the small number of joints meant there was little escape to atmosphere but the areas
around the corners became hollow and dry and suffered most from floor heating stresses
whilst adhesive in the centre of the tile became wet and stayed wet. Further tiles will need
removing to thoroughly dry the calcium screed still affected by moisture and then re-tile
using an adhesive less susceptible to damp.

So if using a gypsum adhesive onto an un primed or primed as this one was then can the moisture from the adhesive going into the substrate rise and then soften gypsum adhesive back up and knack them...

We know that gypsum does not like water to a certain degree but quite worrying to read this... some members might know where that info quoted came from , hence why i posted it here just to getting Alan's feedback or anyone who has an answer..


it is to be noted that some gypsum adhesives say not to prime , so if this moisture can migrate back into the adhesive bed and then cause it to soften then what bloody good is it.?

 

[Ajax123]

Where in the country is th issue dave? I know gypfix has had a couple of issues on bardon high flow in the southwest but I am nt aware of any where else in the country there has been an issue. They have been to do with very damp screed.

Sme clear pics might be helpful as well.

 

[Ajax123]

It is interesting to note that there is an acrylic primer involved here. I just wonder if the primer has held the moisture within the adhesive bed itself. I wold not think unless the scrreed is very wet there wood be enough moisture from the adhesive drawn into the screed to cause this level of softening. It also does not say if the UFH was comissioned and run properly prior to tiling.

 

[DHTiling]

It was a tech spec done after a failure.

 

[Ajax123]

Hmmm. Who specd it??

 

[Spud]

here is my take on the anhydrite screeds and this is just my opinion they work very sucessfully in germany and france but we build in a very different way here in the uk and in some aspects of the building industry we are miles behind ,the last time i worked in Germany it was 1997 and i had worked out there off and on for 4-5 years we went from new build housing sites , supermarkets schools and even tiled water treatment works(**** factories)lol and every job was constructed to near enough the same method ,first a concrete basment shell was made and then the walls were built with red hoolw bricks or calkstein concrete blocks the windows were fitted very early on in the job as they all have rollershutters which are incorporated into box window lintels as soon as the windows are in the plumbers have built a plantroom in the basement and water and gas services are in with a temporary 240v power supply,the plumbera are in early and have ran all the rad pipes and the sparlies have first fixed all the electrics and the the spary plastering is completed and the floor screeding anhydrite in the majority of areas with an sand and cement screed in the bathroom,what i am getting at is the sites are dry and air tight by the time the anhydrite arrives on site this allows the floors to dry out sufficently the floors are always sanded by the screeding contractor and the tilers are not in anyway responsinble for the floor other than a coat of primer before tiling ,we dont build in this way in this country where we dont fit the windows and doors untill much later in the building process sites are not as dry and in the winter often just have a plywood hoarding up and the buidings are often colder and damper than the exterior,our screed companies seem to blast in the anhydrite and leave without sanding the floors and builders seem to be completely unaware of what they have ,how to treat it and when things go wrong some suppliers come out with all the relevant information is on our website I have to prep an agulia 10 screed soon and the info I gained from this site is that the screed must be sanded and expansion joints should be cut every 3m why wasnt this done by the company that supplied the product its like buying a car and ford saying thanks for buying out vehicle but you have to fit the braking system yourself please to refer to our website for the instructions