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-   -   Ardex SLC over flexbone heat (https://www.johnbridge.com/vbulletin/showthread.php?t=130342)

Nick Drake 01-05-2021 01:46 PM

Ardex SLC over flexbone heat
I'm currently in the planning stages on a bath remodel and have been weighing options for radiant heat/uncoupling matts. Narrowed it down to using ardex's flexbone system or laticrete's offering.

With the flexbone system Ardex advertises that you can use their liguid backer board OVER the uncoupling membrane to encase the cables.
However they don't expand on the method in their TDS and I haven't had any luck finding any first hand accounts. Anyone used this system yet and have thoughts/feedback?


Nick Drake 01-05-2021 02:19 PM

Some more info on the project:

Home is 59 build with 1x6 T&G solid sawn subfloor, will be running 2" screws direct to joists. If there are significant high spots I'll sand down before adding the underlayment. Will use a 19/32 acx underlayment with 1.25" screws at 4" on edges and 6 in the field. I *anticipate* that this may still not meet flatness requirements for LFT. I'll be technically over tcna specs to lft with 11x13 hexagons, but mostly I'd just like to have a nice flat surface to set on. I've made the mistake of not getting a flat enough substrate in the past, will not ever do that again.

Going with the full ardex system I'm seeing good time savings, considering I'm doing the work on weekends/evenings this a large factor:
  • Day 1
rapid set mortars to bond the uncoupling matt to the ply underlayment. Run heat cables and apply the liquid backer SLC that evening.
  • Day 2
Waterproof with 8+9 and I'm able to snap chalk lines, plan layout and maybe even start setting the floor that same afternoon (planning on layout with hexagons to take a while)

If I went with the laticrete strata system with it's "hydration vents" the uncoupling benefit is lost if I pour SLC above. Laticrete is very direct in their TDS language that you can pour NXT level plus to prefill, but do loose all So for laticrete I'm looking at:
  • Day 1
Primer the ply underlament, apply ardex liquid backerboard (only SLC available locally which does not require a lath over ply and has a lower minimum depth for SLC on wood substrates).
  • Day 2
Apply strata matt with a rapid set thinset. Run heat cables and then prefill the uncoupling membrane that evening.

Now I'm waiting until day 3 to apply any waterproofing, given the day job constraints that means doing the work Monday evening at the earliest. I can't start snapping chalk lines until Tuesday evening at the earliest, definitely no setting until Wednesday....

smifwal 01-05-2021 05:10 PM


Nick Drake 01-05-2021 06:01 PM

Thanks Shawn, they have some good content on there! Sounds like the install went as smooth as advertised, doing the prefill with the SLC sure seemed less taxing than pushing around thinset :)

Noticed he only used a placer to spread the SLC after troweling it in the detail areas. I've used a gauge rake and spiked roller for SLC to make getting the pour depth virtually idiot proof and keep that surface tension broken up. Seems like they might not work as well rolling over the bumps in the membrane....

smifwal 01-05-2021 06:58 PM

The bumps in the flex bone are like gauge pins,. And the spike roller would be unnecessary since you are just "filling" the voidsno need to break the tension

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