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backer board over radiant floor boards

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WillyP
WillyP Member Posts: 48
I have heard conflicting answers about using concert backer board over warmboard or in my case Sunboard (thank you for recommending them). My plan is to install the pex tubing boards, cover them with backer board, then tile over the top. Is this a terrible idea? Has anybody done that successfully? With my skill set, this would be the easiest way to do it.

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  • hot_rod
    hot_rod Member Posts: 22,131
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    From a temperature standpoint. If so the manufacturer should have a temperature number in mind.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • WillyP
    WillyP Member Posts: 48
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    From what I can see, it is safe up 200° F. I am more concerned with the thermal mass.
  • ethicalpaul
    ethicalpaul Member Posts: 5,702
    edited December 2020
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    I did Uponor Quik Trak in my bathroom...IIRC Uponor recommended setting a concrete board layer on top of the track board. Out of curiosity, what other way would you do it? And what is the thermal mass concern?

    Yeah, here's the manual: https://www.pscia.com/ASSETS/DOCUMENTS/ITEMS/EN/uponor-a5060761-install-instructions.pdf

    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • TAG
    TAG Member Posts: 755
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    Take a look at the Warmboard instructions -- they have 6 ways to tile over. My installer is old school -- did more of full wet bed for the bath floors. Same for the one large shower floor. In the other bath I wanted to do the walls with some tube as part of the shower touches an exterior stone wall -- we just went over the Warmboard treating it as if the grooves were not there
    WillyP
  • Rich_49
    Rich_49 Member Posts: 2,766
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    Use Hardi backer of the 1/4" thickness . This is what SunBoard recommended for their SunFoam product before Graphite pricing went crazy . The R value of the added backer is not an issue
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 22,131
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    CBS "cementitious backer systems" are needed you you are installing ceramic tile., if you follow the tile council recommendations. For wood or linoleum it is mainly an good backer system.1/4 plywood would also work for a backer for glue down or floating floor, might be easier to work with.
    The cement board does add a small amount of thermal mass, and would spread the heat laterally from the tube area also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    ethicalpaulHomerJSmith
  • WillyP
    WillyP Member Posts: 48
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    I am using ceramic tile. That is why I plan on putting down backer board.
    ethicalpaul
  • WillyP
    WillyP Member Posts: 48
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    To answer ethical Paul I read in another forum that the backer board doesn't work well because it has too much air space in it. But I now realize whoever wrote that, didn't know what they were talking about. At least that is what every expert I have spoken to has said.
    With pex in concrete (which I will do on the first floor) the concrete heats up and holds heat due to its mass. I was afraid that backer board wouldn't do that.
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 22,131
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    There are some foam core backer board, a poly-iso core, I would not use that type.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • WillyP
    WillyP Member Posts: 48
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    Mr Rohr while I have your attention. By any chance, do you know the normal exit temperature of water, when it leaves a slab in a pex in concrete slab application. It will be entering at apx ninety five degrees.
  • hot_rod
    hot_rod Member Posts: 22,131
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    The temperature will vary as the slab starts and as it warms. You may see a wide ∆ on cold start, it closes as the slab warms. There really is no one exact number. If you designed for a 10° delta you may occasionally see that.

    If it enters at 95, exits 85 the AWT= 90.
    Surface temperature of say 82 in a 68° room would be about 28 btu/ hr delivered to the space.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    WillyP
  • PC7060
    PC7060 Member Posts: 1,159
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    Concrete backer board must be set over a bed of thin set and mechanically anchored per the schedule. Just be careful where you set the edges and screws since you have radiant piping. 
  • HomerJSmith
    HomerJSmith Member Posts: 2,441
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    The governing factor, I would think, is the R rating of the substrate. The lower the R factor the better it is.
  • WillyP
    WillyP Member Posts: 48
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    Paul. I plan to just use a sharpie to mark the studs on the outside wall. Then as I lay each piece I mark the pipe on top of the sheet.
  • Sukhoi29SU
    Sukhoi29SU Member Posts: 83
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    @WillyP ; how’d it turn out?  I just received shipment of sunboard silver panel and have about 1600sf to install. Will be installed over 3/4” advantech subfloor. 
    Thanks in advance for any lessons learned 
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
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    Concrete backer board is used when tile is to be set over a radiant panel like QuickTrac or Viega Climate panels. It does not have to be set in a bed of thinset, but is anchored to the panels and subfloor with screws. Holes need to be pre-drilled to ease the install of the fasteners. Since there's tubing below, staying 2" away from the tubing is a good idea. Hence, the clear plastic template with the tubing outline.
  • Greg_Neu
    Greg_Neu Member Posts: 1
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    @ Paul, I made my own above-floor sleepers using 3/4 ply. I hear conflicting stories as to setting the backer board using thinset. According to hardybacker the thinset is used primarily to even out the floor so it lays flat. Not having to put down thinset would save an a lot of time installing the backer but I wouldn't want to sacrifice the longevity of the floor by skipping this step. Should I at least fill in the ruturns or any area where there are small negative
    spaces? Appreciate your opinion, this is my DYI project.
  • PC7060
    PC7060 Member Posts: 1,159
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    Read the manufacturer data sheets; every applications I’ve used required the thinset to ensure all voids are filled. 
    ethicalpaul
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
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    If the floor or QuickTrac panels are level, there should be no voids in the backer board if secured with proper screws countersunk and holding it down. Gaps in panels are typically filled with 1/2" ply before doing the backer. I've never used thinset to secure the backer.
  • ScottSecor
    ScottSecor Member Posts: 855
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    We typically use thinset with backer board. It does add to the install time (and materials cost). I would say it adds about two or three man hours (assuming materials are already at jobsite) for a roughly two-hundred square foot room install.
  • PC7060
    PC7060 Member Posts: 1,159
    edited February 2022
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    What @ScottSecor said, following the manufacturer technical data sheet is key. the thin-set is critical to prevent backer board flex and help ensure the tile has a solid and stable decoupling layer.