backer board over radiant floor boards

WillyP

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.

hot_rod

From a temperature standpoint. If so the manufacturer should have a temperature number in mind.

WillyP

From what I can see, it is safe up 200° F. I am more concerned with the thermal mass.

ethicalpaul

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

TAG

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

Rich_49

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

hot_rod

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.

WillyP

I am using ceramic tile. That is why I plan on putting down backer board.

WillyP

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.

hot_rod

There are some foam core backer board, a poly-iso core, I would not use that type.

WillyP

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

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.

PC7060

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. 

Paul Pollets

I make an outline of the tubing layout using a sheet of clear plastic and a Sharpie, cutting the plastic sheet to the exact size of the room. After the tubing is traced the backer board can be set and the plastic sheet layed over the top to see where the tubing is. This allows easy screwing of the backer board without fear of hitting the tubing.

HomerJSmith

The governing factor, I would think, is the R rating of the substrate. The lower the R factor the better it is.

WillyP

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

@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

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

@ 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

Read the manufacturer data sheets; every applications I’ve used required the thinset to ensure all voids are filled. 

Paul Pollets

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

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

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.