underfloor heating + ply + tiles

[boghog]

My plumber installed an underfloor heating system, and initially I was under the impression that he will screed over the heating. I told him I want to tile the floor. Now he told me that he can't screed it because of the beams/joists and instead he will ply over, which he thinks will not be a problem for tiling. Can anyone confirm this? Doesn't the ply expand due to the heating and won't that crack the tile adhesive? Does anybody have experience of that goes in between the underfloor heating and the tiles?
Also, I would like travertine. Does that change anything?
Thanks

 

[Karis]

What sort of UFH is this?

 

[boghog]

Hot water. I think the make is Wunda

 

[Karis]

My plumber installed an underfloor heating system, and initially I was under the impression that he will screed over the heating.

Why did you assume that? Did you not get a detailed quote & a signed contract specifying exactly what he was going to do?

Now he told me that he can't screed it because of the beams/joists

Not entirely true.

instead he will ply over, which he thinks will not be a problem for tiling. Can anyone confirm this?

Ply wouldn’t be my choice over a wet UFH system but it depends how it’s done. Frankly, I’m always very suspicious of plumbers doing tiling!

Doesn't the ply expand due to the heating

Yes, & differential movement of the ply will be a major factor; it’s not ideal.

and won't that crack the tile adhesive?

If it’s not done correctly using the correct materials, yes.

Does anybody have experience of that goes in between the underfloor heating and the tiles?

Tiling over UFH of any sort is a little more involved & suspended timber floors need additional consideration/prep & the tiling materials aren’t cheap. A between joist screed overlaid with a cement backer board would be ideal with a wet system but if you didn't get a spec, don’t have a fixed price & he’s charging materials + time, you could be in for a shock either way. Alternatively, if he’s skimping, you could end up with something that will fail fairly quickly.

Also, I would like travertine. Does that change anything?

Personally, I think Trav is poor choice for any floor for many reasons + it can be high maintenance but it rather depends on quality, how it’s laid & how it’s finished off.

Before you go any further, I think you need to ask you “plumber” for a detailed spec of the prep he will do & materials he intends using & post it here for comment.

 

[boghog]

Why did you assume that? Did you not get a detailed quote & a signed contract specifying exactly what he was going to do?

He did give me a detailed quote and he told me they were going to lay a screed on top of everything (half of the space is concrete and half was floorboards).

Ply wouldn’t be my choice over a wet UFH system but it depends how it’s done. Frankly, I’m always very suspicious of plumbers doing tiling!

He is not doing the tiling, I will get a tiler to do that. He was just going to leave a screed or something that I can get someone else to lay the tiles on. He is not even doing the screed, he is subcontracting a builder to do that work.

Yes, & differential movement of the ply will be a major factor; it’s not ideal.

So what can I put there?

If it’s not done correctly using the correct materials, yes.

So are there any materials that would make it ok even with the ply?

Tiling over UFH of any sort is a little more involved & suspended timber floors need additional consideration/prep & the tiling materials aren’t cheap. A between joist screed overlaid with a cement backer board would be ideal with a wet system but if you didn't get a spec, don’t have a fixed price & he’s charging materials + time, you could be in for a shock either way. Alternatively, if he’s skimping, you could end up with something that will fail fairly quickly.

He didn't mention any price change yet, even though he is running a bit late now.
He seems a very nice guy, I don't expect any nasty surprises. If something else needs to be done, I would rather get it done properly. So should I ask him to screen over the joists anyway, despite his recommendation for the ply layer?

Personally, I think Trav is poor choice for any floor for many reasons + it can be high maintenance but it rather depends on quality, how it’s laid & how it’s finished off.

Before you go any further, I think you need to ask you “plumber” for a detailed spec of the prep he will do & materials he intends using & post it here for comment.

I don't know much about tiles, I just loved the look and feel of the travertine. I thought that with a very good feeler/seal it will be just as good as ceramic or porcelain, or at least so I was told at the shop.

I went back to check the quote and it doesn't mention the building work, just the plumbing items. I guess I missed that at the time, but I am sure he confirmed it all verbally. Besides, his builder did already put in a lot of effort as he had to take out a couple inches of the previous screed in half of the area.

Thank you for your comments. Can you please advise me further?

 

[Karis]

half of the space is concrete and half was floorboards.

Is the wet UFH system installed over both floors? If so what's been done as fgar as the scredd goes?

Having two different floor bases complicates things somewhat for tiling & requires special attention/preparation let alone the further complication of a UFH system. The two floor bases will expand & contract at different rates which will always cause cracks where the two meet if it’s not done properly.

More info would be very useful; why do you have ½ concrete & the other ½ on a suspended floor, is this work part of a new extension? Anything else I need to know?

 

[boghog]

Half the space is an extension built in '90 which has a concrete base, with a screed on top. The other half is an old suspended floor with old floorboards.
I wanted a hot water heating system, and the concrete floor was too high so they had to break the screed and take it off. That was quicker than I expected.
Not they have laid insulation everywhere, and the pipes go over the concrete floor and in between the joists in the other half. They are backed by some foam boards with insulation on top in between the joists. That is about it I think.
Now they will lay another screed on the concrete half, and over the suspended floor they said they will put ply. After some googling I insisted that the ply is at least 22mm thick.
All of this will be covered in tiles, still not decided which tiles but as I mentioned above I love the look of travertine. I am slightly put off by the amount of maintenance required though.

 

[Karis]

Tiling over two different substrates is not ideal; it will crack due to differential expansion where the two meet unless you use an expansion joint or an uncoupling membrane but that won’t necessarily work either with the UFH. Insist they re-screed the whole area or you will be letting yourself in for some serious grief.

Personallly I wouldn't bother with the trav, pick something more suitable for a heavy load/traffic area.

 

[boghog]

This will be a tough one, they were convinced for some reason that they can't screed over the suspended floor and it has to be ply.
Can't I cover the screed & ply with something else of the same material before laying the tiles, to solve the problem?
Alternatively, if they were to screed, then wouldn't the screed go only in between the joists, creating the same problem where the wooden joist meets the screed?
With regards to the tiles, if travertine is frowned upon what would make a better choice? Granite or ceramic?
This is not heavy (as in commercial) traffic, but it is the living room and kitchen and I have a couple dogs that run and scratch around as well.
Thanks