Thickness of flexible tile adhesive for terracotta tiles on anhydrite screed

[DHTiling]

Just a thick bed flexible adhesive to around 10mm deep is easy sufficient IMO..

 

[Perry]

nothing wrong with thick bed adhesive i used over 200 tons the year before last(not well last year not working) but you would grade the tiles a little as you were laying them so you shouldent need a 25 mm bed

 

[Perry]

if its a height problem you need to build the floor up then tile it

 

[Perry]

what area are you piggy ?

 

[piggy]

ok - I accept that we've left too big a gap and that 10mm may be enough adhesive but that still leaves a 15mm gap to fill.

Given the anhydrite screed, ufh and the 25mm gap what do you think are my best options?

 

[piggy]

Yeah maybe - what would you recommend?
We are in Pembrokeshire, West Wales.

 

[Perry]

AAAAAAAjax what do you think not my field what would be cost affective ?

 

[Perry]

does the whole floor need to be raised or can it bee ramped ?

 

[Ajax123]

If you are simply looking at the depth in order to void fill a gap and you are looking at a 10mm adhesive bed then the best thing would be to use a levelling compound over the screed to fill most of the void first. Use a gypsum based compound such as NC110 from Uzin or Screedmaster Gypsum from Laybond Products at 15mm. Because they are gypsum based they are compatible with the screed and will not noticably impede the thermal performance of the floor. You could then use a gypsum based tile adhesive to stick the tiles down e.g. Weber Anhydrite.col or GBTA from creative impressions.

 

[piggy]

does the whole floor need to be raised or can it bee ramped ?

Whole 100M2 unfortunately!

 

[piggy]

If you are simply looking at the depth in order to void fill a gap and you are looking at a 10mm adhesive bed then the best thing would be to use a levelling compound over the screed to fill most of the void first. Use a gypsum based compound such as NC110 from Uzin or Screedmaster Gypsum from Laybond Products at 15mm. Because they are gypsum based they are compatible with the screed and will not noticably impede the thermal performance of the floor. You could then use a gypsum based tile adhesive to stick the tiles down e.g. Weber Anhydrite.col or GBTA from creative impressions.

Thanks for going into this in depth - Have had a look at gypsum based adhesives but are they OK to use in exterior doorways, kitchen, utility and cloakroom with shower or any place where they may get wet?

 

[Ajax123]

Thanks for going into this in depth - Have had a look at gypsum based adhesives but are they OK to use in exterior doorways, kitchen, utility and cloakroom with shower or any place where they may get wet?

I get asked this all the time with regard to the screeds. My answer is this. The calcium sulphate screed should not be used in areas where it will become wet or in areas where it will remain permanantly wet. in respect of the screed material itself temporary wetting is not considered a problem. If the screed is dried then covered with a floor covering it is sealed against the ingress of moisture so will not become wet and so does not present a tangible problem. My opinion is that the same advice should be followed with the smoothing compounds and tile adhesives. you would use a standard flexible cement based grout and silicone around the perimeter expansion gap.

If a cement based smoothing compound is used over a gypsum based screed and it gets wet it WILL delaminate from the screed and the flooring will fail. If a gypsum based smoothing compound is used the floor covering itself may delaminate (in the case of tiles they would be reusable if a gypsum base adhesive were used) but the smoothing compound and adhesive would generally remain bonded to the screed.

In areas where there is high risk of moisture ingress e.g. commercial kitchens the I would always recomend the use of an epoxy damp proof membrane over the screed prior to tiling anyway. If this is done then a cement based adhesive would be more appropriate.

I know of hundreds of thousands of square meters of tiles on gypsum adhesives in kitchens, bathrooms, utility rooms etc and there are no serious issues. Won't say there are no issues at all because the human element often comes into play and you find someone has done something daft.