Tiling over overfloor heating system - Wundafloor - Tile Advice

[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?