General tiling advice, decoupling membranes and products - TilersForums.com

[WillCalderwood]

Hi All, this seems like a fantastic knowledge-base for tiling online.

We're currently doing up our house with assistance from my brother. He's done a bit of DIY tiling before but doesn't have huge experience. We've got 2 tiling jobs:

The first area we're tiling a large kitchen diner, approximately 27m2 of floor. We're looking at travertine tiles. They are being laid onto anhydrite screed. I know we have a few things to consider here. Firstly, we need to make sure the screed is properly dry, secondly we need to seal it (Anyone got any product recommendations?) We also have wet underfloor heating. Do we use a decoupling membrane? From what I've read it sounds like we probably should, I just wanted to double check. Also, do people have recommended adhesives, grout and techniques using travertine on anhydrite screed with UFH?

The second area is a small bathroom, approximately 1.5m x 2.5m floor area. We're looking at a porcelain floor tile, wall tile has yet to be decided. This is fairly solid suspended timber floor, 100+ years old. Joist spacing is across the 1.5m span with spacing between the joists varying between 250mm and 320mm, so no large spans. We've secured 18mm WBP ply on that. Again, we have UFH. The same questions here, do we use a decoupling membrane? I know it'll do nothing for flex in the floor, but was wondering about expansion and contraction of the ply? Any other recommended products with regards to adhesion and grout? Also with regards to sealing the ply, I've read about sealing the back to prevent absorption of moisture from the air below. Is this a requirement or a nice to have?

Thanks in advance for the advice.

 

[Ajax123]

The kitchen is relatively straight forward in terms of using a decoupling membrane the answer is yes.

You do need to make sure the screed is suitably dry and also that heating has been run through the heating cycle based on manufacturers instructions. If you have no instructions let me know and I can e mail a generic procedure to you.

In termsof preparation products it depends on a number of variables but essentially you will need to lightly abrade the screed surface and then either prime it with a primer recommended by the adhesive supplier. The adhesive is the driving factor in tha if you use a cement based adhesive to stick the membrane down yo are btest to use a water dispersion le epoxy primer. If you use a gypsum based adhesive then a simple acrylic will suffice. The other school of though and I have to agree there is some merit to it, is tha you can use a vynil flooring the adhesive to stick the membrane down. On top of the membrane you can se a standard white flexible spcement based adhesive.

In the bathroom as it is ply I shall let the tilers on here answer that bit.

 

[WillCalderwood]

Thank Ajax, that's really useful. I did receive advice from the screed company about force drying and commissioning the UFH. One question with regards to primers. Why do you say to use an epoxy sealer for cement based adhesive? The screed company said to use acrylic, and I've just done some Googling, but can't find any definite answers. It sounds like the Expoy might be more hard wearing?

If anyone could advise on the ply that'd be much appreciated and we hope to start tiling tomorrow!

Cheers.

 

[Ajax123]

Epoxy will inhibit the migration of moisture borne sulphates (bear in mind tha you screed will never be 100% dry) these sulphates can react with the adhesive and cause delamination.

Acrylic is much less effective at stopping this migration.

Its about managing the risk really. Epoxy is not significantly more expensive than acrylic square meter for square meter and certainly cheaper than having issues down the line.

 

[WillCalderwood]

Thanks for that Ajax,
I've been doing more reading, and elsewhere on the forum you're suggesting the use of gypsum based adhesives as the best solution to the gypsum/cement issues. Most of the threads I read were getting on for 2 years old however. Would you still advice this as best practice? If so, which adhesive would you advise as being most appropriate for our floor? To me, this seems like the most sensible solution. I found the Kerakoll H40, which I've found recommended in a few places, for £30 a 25kg bag inc VAT which seems an ok price.

I feel like I should be concerned about gypsum based screeds and moisture, as I'm sure you know gypsum is soluble in water. However, the H40 they say is for internal and external use, which would suggest this issue has been somehow resolved.

Thanks again.

 

[Mark S]

Will,
You have been given some good advice re preparation of the anhydrite screed, there are basically 2 systems you can use
1, prime the floor, after sanding/abrading to open the surface, with which I would recommend an acrylic primer, and then tile. What I would recommend is that you use 1 manufacturer for the primer and the tile adhesive.
2, sand as above and use something like the Kerakoll H40 Ideal.
In both cases ensure the floor heating has been correctly commissioned, and the screed is dry, and the heating turned off, I came across a floor the other week where the heating was still on when the tiling was installed.
I hope this helps

 

[Ajax123]

Thanks for that Ajax,
I've been doing more reading, and elsewhere on the forum you're suggesting the use of gypsum based adhesives as the best solution to the gypsum/cement issues. Most of the threads I read were getting on for 2 years old however. Would you still advice this as best practice? If so, which adhesive would you advise as being most appropriate for our floor? To me, this seems like the most sensible solution. I found the Kerakoll H40, which I've found recommended in a few places, for £30 a 25kg bag inc VAT which seems an ok price.

I feel like I should be concerned about gypsum based screeds and moisture, as I'm sure you know gypsum is soluble in water. However, the H40 they say is for internal and external use, which would suggest this issue has been somehow resolved.

Thanks again.

where normal ceramic or porcelain tiles are concerned I would recommend gypsum based adhesives ... You are correct. This has not changed but is based on the fact that no uncoupling membrane is likely to be needed with these tile types.

However the British standard for the installation of natural stone tiles such as travertine, your chosen tile type, to heated screeds makes a specific recommendation about uncoupling the tiles from the screed. This is primarily because many natural stone tiles are not resilient to thermal expansion and contraction due to the natural veins within the tiles. They can crack when they move. The use of an uncoupling membrane significantly reduces the types of stresses that cause these cracks and so I am in agreement with the British standard in this part. This recommendation is also supported by the British stone federation. I have been unable t find a membrane manufacturer who is comfortable to recomend using a gypsum adhesive to stick their mat down and as such my hands are tied. No point in recommending a system that you would be unable to get any sort of warranty for.

The recommendation to use epoxy in preference to acrylic is borne out of experience. I have seen many failures where acrylic is used and almost none where epoxy is used. Mark S is correct in as much as the industry in general will recommend acrylic. I do not share that view simply because of the experiences I have had.

H40 ideal is certainly an option for sticking down the Ditra but don't do it on a primed screed.

Your concern about the solubility of gypsum in moisture from the screeds perspective is not necessary unless you intend to regularly and persistently flood your floors which i doubt. However residual moisture, underfloor heating and floor coverings is an issue because it is difficult to stick a floor covering to a screed with high humidity and so you need to make sure your screed is suitably dry.

Hope this helps.

 

[Andrew]

"

H40 ideal is certainly an option for sticking down the Ditra but don't do it on a primed screed.


I presuming this is because the moisture needs to disperse and if the screed is primed and the ditra is waterproof there is nowhere for the moisture to go
​

 

[Ajax123]

"

H40 ideal is certainly an option for sticking down the Ditra but don't do it on a primed screed.


I presuming this is because the moisture needs to disperse and if the screed is primed and the ditra is waterproof there is nowhere for the moisture to go
​

Yep

 

[WillCalderwood]

Does anyone have an Epoxy primer they can recommend?