Tiling over overfloor heating system - Wundafloor

[Shinyshiny054]

Hello,
I’m new to tiling and to forums so my apologies for both if there are any etiquette failures!

I’ve scoured the internet and can’t find any tangible advice on tiling on over overfloor heating. We installed the Wundafloor EPS 400 system ourselves (other half and I) and are concerned about the loops which sit proud of the boards. I called Wundafloor and the advice was to tape the loops down. We’d already done this but pushing on the loops with a foot still allowed a fair amount of bounce. We were told that Granfix ultimate flex with ultra prime it would provide enough protection to the tiles from th bounce. We are doing an entire ground floor so naturally I’m concerned being a) a complete novice and b) that we lay it all and the tiles crack or lift.

Has anyone laid tiles over such a system and what are your recommendations? Will we be ok with the adhesive only, will it absorb the bounce as we’ve been advised? We have limited height to which we can tile, but we’re planning on a 10mm adhesive layer (though have been recommended 6mm by Wundafloor)

Tiles are porcelain 605x605mm

Many thanks

Gill

 

[Lee@emctiles]

Hi Gill, have you tried calling Granfix to check this procedure is adequate?

From personal experience, my method of these type of UFH systems i would recommend laying a flexible levelling compound.

a quick call to Granfix might be a good idea 01827 871871

 

[Flintstone]

There are a few types of these systems can you tell us the set up please. Solid floor? Floating insulation with pipes in? Stuck down? Made of gypsum? Got foil on the face? Timber floor?

 

[Shinyshiny054]

The type of floor is concrete base (that house was built on), stuck down panels with foil face and pipes pressed in (pretty tight loops which resulted in lifting pipe). Part of the floor, an extension, is suspended floor with wood chipboard. The same panels were used here, we’ll use an expansion gap so there’s no tiles spanning existing house and new. Have attached a photo of the system taken while we were laying it, it’s too dark down there now to photograph the level of lift I’m taking about but possibly a few mm

 

[Flintstone]

Personally I wouldn’t tile it. You cant tile to the foil surface or use a cement based product. Perhaps @3_fall might be able to advise better

 

[Shinyshiny054]

Personally I wouldn’t tile it. You cant tile to the foil surface or use a cement based product. Perhaps @3_fall might be able to advise better

Thanks for getting back to me. The instructions from Wundafloor specifically state you can tile it, using a primer, and we bought the system on the premise that we could. I called them about the bounce and they were confident in the fact it can be tiled. I really hope it is the case because it’s all primed and ready to go as soon as we have a child free day!

 

[Flintstone]

I’d hold your horses before you get the correct info. Read this link and follow the links within it and tell me what you think

Preperation - Advice on tiling onto "overlay" underfloor heating - https://www.tilersforums.com/threads/advice-on-tiling-onto-overlay-underfloor-heating.84747/#post-884476

 

[Old Mod]

Hey Gill,
Andy’s (local) is quite correct, this type of system is subject to a high rate of failure because of incorrect preparation generally.
It’s not a product I would tile, these systems are primarily aimed at the laminate and soft flooring finishes, but they do state the 400 series is suitable for a hard tile finish.
If I could be convinced totile one of the systems, I would have to insist on this product being used.

https://www.wundatrade.co.uk/shop/home/accessories/tools-accessories-2/4mm-backer-board/

It’s a 4mm board designed to cover the Wundafloor And give a tillable substrate. Although in their literature they state it’s an optional extra, I would suggest don’t even think of Tiling it without it.
It creates a barrier between the Aluminium and cement based adhesives. And it’s far more effective than any primer they suggest.
In essence, the cement adhesive can react with the Aluminium and produce hydrogen gas and cause the adhesive to become weak and fail.
That’s based on research undertaken by myself and a colleague.
Please don’t think that ufh or adhesive companies will substantiate that, cos they won’t, why would they.
Do your own research, it’s there to be found quite readily.
(Reaction between Aluminium and Portland cement)
So as you’ve made your investment, I would strongly suggest the use of the above product.
Still prime as suggested and adhere the boards how they dictate, then tile it.
I would ask them for a ‘method statement’ to be emailed to you, and as long as you follow the instruction to the letter, that’ll be as safe an install as you can manage.
Are you tiling it yourself or do you intend to hire a fixer?
As far as your adhesive bed is concerned, a 10mm notch trowel will produce an approximate 3mm solid bed of adhesive.
Make sure that you skim the back of the tile with a thin layer of adhesive with the flat edge of your trowel prior to bedding it in to the adhesive. This will improve bond strength by 50%
It does sound like a mammoth task for a diy installation I must admit.

 

[Flintstone]

Good post. I’ve not seen those boards before, what are you supposed to stick them down with ?

 

[Shinyshiny054]

Thanks Localtiler and 3_fall for your responses.

If we coated with 2 or 3 coats of the primer, could we still be in hot water with the reaction between the aluminium and the adhesive?

If we were to go with the backer boards, will this help with the ‘bounce’ described with the pipes which don’t quite fit snug into the loops. The advice we were given is to tape down the loops, but they still move which makes me think that they’re weak spots waiting to happen once adhesive and tiles are on (ie air space under the loops). That was my original concern but now it’s grown arms and legs!

Thank you for taking the time to answer, it is a bit of an extreme diy I must admit...

 

[Shinyshiny054]

@Localtiler they’re stuck with a spray adhesive that was supplied by Wundafloor. Seems to have stuck them pretty fast - we made a mistake with one and it destroyed it ripping it back up once dry!

 

[Old Mod]

One part of their installation process states you can loose lay the boards, under no circumstance do this. They MUST be adhered to the eps boards.
As to whether it will stop the pipes from lifting, I would only be guessing.
Are you able to charge the system yet?
If so, pressurise it to 5-6 bar cold and see how they lay then.
The reason I say 5-6bar is because this will approximately mimic the expansion of the system when hot at 1-2bar when operating.
If the water weight holds them down, then with the backer board on top, it may well suffice.
I can’t confidently comment on ultra’s msp primer (multi surface primer) being sufficient to give you a successful install.
I could suggest that you contact our sponsor Isomat, there is a link below this thread, speak with Marek and ask if their primer Supergrund is suitable for use on this Aluminium system. The reason I suggest that particular primer is because it is resin based as opposed to acrylic or sbr based primers, and hopefully may be more resilient.
And then you could latex over the boards giving you a substantial increase in weight over the pipes. That is pure conjecture on my part tho, but Marek will contact his R&D department for you and give an unbiased opinion.
Tell him Marc from the Forum sent you.
Their technical backup is very good and they will stand by their products.
Other than that Gill, that’s about as much advice I can put your way I’m afraid.

 

[Shinyshiny054]

One part of their installation process states you can loose lay the boards, under no circumstance do this. They MUST be adhered to the eps boards.
As to whether it will stop the pipes from lifting, I would only be guessing.
Are you able to charge the system yet?
If so, pressurise it to 5-6 bar cold and see how they lay then.
The reason I say 5-6bar is because this will approximately mimic the expansion of the system when hot at 1-2bar when operating.
If the water weight holds them down, then with the backer board on top, it may well suffice.
I can’t confidently comment on ultra’s msp primer (multi surface primer) being sufficient to give you a successful install.
I could suggest that you contact our sponsor Isomat, there is a link below this thread, speak with Marek and ask if their primer Supergrund is suitable for use on this Aluminium system. The reason I suggest that particular primer is because it is resin based as opposed to acrylic or sbr based primers, and hopefully may be more resilient.
And then you could latex over the boards giving you a substantial increase in weight over the pipes. That is pure conjecture on my part tho, but Marek will contact his R&D department for you and give an unbiased opinion.
Tell him Marc from the Forum sent you.
Their technical backup is very good and they will stand by their products.
Other than that Gill, that’s about as much advice I can put your way I’m afraid.

If anything @3_fall the pipes seem to ‘tense up’ when we run the system and lift higher than when off! Thanks for the advice, it’s been very helpful. I will email Wunda and ask for a method statement and see if I can get any further advice based on your recommendations. ☺️

 

[Old Mod]

If anything @3_fall the pipes seem to ‘tense up’ when we run the system and lift higher than when off! Thanks for the advice, it’s been very helpful. I will email Wunda and ask for a method statement and see if I can get any further advice based on your recommendations. ☺️

Daft question hopefully, did you run the pipes out correctly?
By that I mean unroll, not just lay them down off the coil.
Does that make sense?
Imagine a roll of cable or hosepipe, if you correctly unroll them they don’t twist.
If you lay out the coils to the side for example, you get unnatural twists in the cable or hosepipe.
I’m only guessing obviously, but I can say I’ve not heard of the problem of the pipes lifting free of the boards, sounds like they are twisted to me, and when you pressurise the system it emphasises the twist causing them to lift.
Like I say, it’s just a guess.

 

[Shinyshiny054]

Daft question hopefully, did you run the pipes out correctly?
By that I mean unroll, not just lay them down off the coil.
Does that make sense?
Imagine a roll of cable or hosepipe, if you correctly unroll them they don’t twist.
If you lay out the coils to the side for example, you get unnatural twists in the cable or hosepipe.
I’m only guessing obviously, but I can say I’ve not heard of the problem of the pipes lifting free of the boards, sounds like they are twisted to me, and when you pressurise the system it emphasises the twist causing them to lift.
Like I say, it’s just a guess.

I know what you mean, we tried to lay them in following the turns of the roll as much as possible, probably why some are better than others. We’ve had some luck scraping out the polystyrene under the loops and that seems to help keep them down, there are a lot of loops to get through though.

I have emailed them with all the questions I have and points you have raised so I have something in writing. OH advises me that they referred him to their brochure when he emailed questions though, and attached a PDF We’ll see what comes back from them this time

 

[Shinyshiny054]

Ok so I called and spoke to Alan, Tech Support for Granfix/prime it. He advised that a neat 100% coverage, single coat of Ultra Prime It is sufficient in creating a seal between the aluminium and adhesive preventing the chemical reaction mentioned above.

We had used aluminium tape as per advice from Wundafloor to stick down pipes which had a bit of bounce at the loop but were concerned that the prime it wasn’t sticking properly. He agreed that there is an issue with aluminium tape and to remove all of this, instead using an alkaline resistant mesh (Skrim) tape to stick down any problem spots, the benefit being the adhesive can be pressed through it and around the pipes. The weight of the adhesive/tile should prevent any issues when dry.

He advised 6mm notched trowel gives 5mm bed thickness which will be sufficient together with back buttering of tile and in filling the joints and pipe runs with adhesive. Can anyone recommend a trowel for this? We overestimated and have a significantly higher notch.

 

[Dumbo]

A 6mm notch trowel will not give a 3mm bed depth as when you use the trowel you hold at about 45 degrees to the floor therefore the vertical height of your ribs are approximately 7mm . So when you slide your tile on the ribs to collapse the ribs to get full coverage on the tile you will get a bed thickness of about 3.5 mm . It's all to do with Pythagoras and his theory .

 

[Shinyshiny054]

A 6mm notch trowel will not give a 3mm bed depth as when you use the trowel you hold at about 45 degrees to the floor therefore the vertical height of your ribs are approximately 7mm . So when you slide your tile on the ribs to collapse the ribs to get full coverage on the tile you will get a bed thickness of about 3.5 mm . It's all to do with Pythagoras and his theory .

@jcrtiling thanks for your reply. I thought that the recommendation sounded a little off given the tables of advice I’d seen online.

What would you recommend trowel wise?

Gill

 

[Dumbo]

I wouldn't tile straight on the pipes . But I would use a large format trowel 20mm wide 15 mm deep . Get granfix to email you what they are telling you about the primer see if they are prepared to put it in writing .

 

[Shinyshiny054]

Yes, I have it all in writing from Wundafloor. The Granfix rep said that anything over 10mm is too deep and will cause issues with drying and contracting and cracking etc. Being a complete novice I have nothing to go on but advice I find online with regards to adhesive depth etc. I’d be keen to get a tiler to do it for me if we had the money and thought we could find someone competent that would take it on. As far as I can see no one wants to do it and I can find little evidence of anyone that has, and I now see why. Too late however, heating system laid and tiles, adhesive and primer all bought.

Just dealing with Wundafloor and Granfix over issues with the primer adhering to aluminium tape... :-(

 

[Shinyshiny054]

@jcrtiling what would you recommend instead of tiling straight onto pipes? Here is the response from Wundafloor re using their backer boards

Me: Are the backer boards you retail recommended to prevent issues with bounce and chemical reactions and what fixing do you advise is used to adhere to the eps 400 boards? Is there much heat loss with these?

Wunda: they are to make it easier to remove the tiles in the future, if a tile got damaged for whatever reason or you just want a different floor finish, this can also be achieved by priming the panel and doing a thin layer of a renovation screed (again recommendation on what to use in the attached fact sheet) to act as an intermediate layer.

 

[Shinyshiny054]

Here is relevant page from the fact sheet from which I can see no recommendation of intermediary layer

 

[Tile Shop]

If you want a second opinion, speak to Mapei Technical. I know they have worked with Wundafloor to come up with a tile fixing spec but not 100% sure if it was foil topped.

 

[Old Mod]

Did granfix admit there was a chemical reaction possible?
To my knowledge ultra recommend their MSP primer noft Ultra Prime It, that’s two separate products.

If you want a second opinion, speak to Mapei Technical. I know they have worked with Wundafloor to come up with a tile fixing spec but not 100% sure if it was foil topped.

Yes Paul, Mapei do indeed have a recommended installation for wunda floor ufh.
Two in fact, one including latex, one without.
Can’t bring them to mind presently.

Gill.
You need to bed your tiles in a solid bed of adhesive. A 6mm trowel will NEVR achieve a 5mm solid bed of adhesive.
The problem is that theses people do not lay tiles for s living, so their installation advice is not based on experience.
As I said earlier, a 10mm trowel will only achieve around 3-4mm SOLID bed.
Experiment yourself, get a piece of glass and trowel a piece of board with adhesive and press glass into it and watch how it behaves. Rock the glass forward and backward so as to collapse the ribs created by the trowel until such time you can see no voids beneath the glass, this is classed as a solid bed, then measure the depth.
Yes a 10mm SOLID BED is much too thick and will be effected by rise and falls in temperature.
That’s where the confusion lies I’m sure.
The difference between terminology used and actually understanding what you’re talking about.

 

[Old Mod]

My mistake, well not mine, the numpty next to me who assured me they were two different primers. According to your pdf above it’s the same thing, apologies Gill.

 

[Flintstone]

I would suggest something like a 10mm trowel on the floor and a 4mm on the back of the tile.

 

[Dumbo]

What i said was get granfix to put in writing what they are saying .

 

[Flintstone]

I still wouldn’t tile it!

 

[Dumbo]

I still wouldn’t tile it!

I wouldn't either i just like making adhesive companies back up what they are saying it's
Surprising how they sometimes change their minds .

 

[hmtiling]

A 6mm notch trowel will not give a 3mm bed depth as when you use the trowel you hold at about 45 degrees to the floor therefore the vertical height of your ribs are approximately 7mm . So when you slide your tile on the ribs to collapse the ribs to get full coverage on the tile you will get a bed thickness of about 3.5 mm . It's all to do with Pythagoras and his theory .

Are you sure you can get a 7mm rib from a 6mm trowel by holding it at 45degrees?