What primer and adhesive - underfloor calcium sulphate - TilersForums.com

[J Sid]

isn't the problem a long time reaction between gypsum and cement where the two touch, could take years to fail ?

 

[Balloo]

As long as larsen pink champagne is not used ,, bal apd and botomen primer only two i like to use

 

[Dumbo]

isn't the problem a long time reaction between gypsum and cement where the two touch, could take years to fail ?

isn't the problem a long time reaction between gypsum and cement where the two touch, could take years to fail ?

Actually I thought it was the other as when both parts were inert ie finished curing that was it . Obviously some things although may not have a good bond from the get go may take time to show the problem . I couldn't see how dry anhydrate and dry cement is going to start reacting maybe @Ajax123 could share some knowledge on this .

 

[J Sid]

just because it's cured doesn't stop the two reacting imho,

 

[Just Rizzle]

I did an alpha hemi hydrate screed where I had to put a cut tile until the next stage of work was completed . When I had to remove said tile to continue tiling , it didn't want to come up , it was well bonded to the screed and that was done with a cement based adhesive .

how long was it down?

 

[J Sid]

Tricalcium Aluminate present in ordinary Portland cement (OPC), contained within tile adhesive will react with the sulphate in the floor screed and cause ettringite to form, and lead to failure I think

 

[Dumbo]

how long was it down?

At least a couple of years but on a side not I have tiles down in my own house which was a new build . Mayhew alpha hemi hydrate screed been 5 to 6 years and they are fine . Same process . Hallway , kitchen , utility and boot room

 

[Ajax123]

No need for uncoupling with porcs. Use gypsum based adhesive e.g. tilemaster anhyfix or similar.

 

[One Day]

I think you have to sand the floor no matter how long the screed has been down, preferably using a MASSIVE diamond grinding machine - and be sure to take off at least 5mm exposing the soft belly of the beast.
Then prime several times with an epoxy primer - preferably dashed with sand for a good key.
Then install Ditra using a gypsum adhesive.
Then commission the heating for a few weeks, being sure to let everything cool.
Then fix tiles using a cement adhesive, and don't forget to perform the rituals and offerings to the manufacturers of Calcium Suplhate before beginning....

(or you could use common sense and listen to the independent experts advice)

 

[On one]

isn't the problem a long time reaction between gypsum and cement where the two touch, could take years to fail ?

On a similar note ....I have a domestic customer who had problems with some solid wall plastering issues.
Turns out the builder/plasterer in the late 90's had first coated the solid stone walls with sand and cement render then second coated with gypsum based bonding plaster then a gypsum finish coat..........the result,albeit 20yrs later......the gypsum had delaminated from the sand and cement render..............
Just my penniesworth!