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Radiant pex under cement/encaustic tile--what is the wait after install?

We had Uponor quiktrak installed in a front door foyer, a small patch like 4 x 6. It's sandwiched to spec: subfloor, layer of ply, quicktrak, 3/8" hardibacker, thinset and then 1/2" cement (encaustic) tiles. Looking around and install instructions for these tiles you get a wide range of instructions for turning the heat on (it has been tested and works) so that the floor doesn't rise or crack or otherwise fail—one said wait 10-12 weeks, which is absurd! Another suggested wait 5 days from install, then put it on a bit, then off, a few cycles to slowly acclimate.
Note that the tiles aren't ceramic or porcelain, they're both much thicker and also more brittle .
Anyone here have experience, and if not, an educated guess on the ideal way to proceed? Note it is 32 out today...


  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Acclimate slowly after 5 days of the adhesive drying. I'd use 2 hr cycles (2 on, 2 off) until floor is at desired temperature
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    I'd turn it on, but if you can control the water temperature for that zone, cool and slow. If you have a thermal imaging camera, you can watch it there.
    There's not a lot of mass with that sandwich like a wet bed or concrete slab. 4x6 should move independently and not require any expansion joints.
    10-12 weeks is a cya move. If anything were to happen they would blame you for not waiting. Probably not necessarily entirely wrong for a fresh poured slab, but I'd have to think the recommendation would still be slow and steady, and cool.
    But slow and steady, and cool should be fine, and how I would do it. After all, that would be like telling you to only install your tile and run the radiant if you know the outdoor and indoor temperature is going to stay the same for the next 10-12 weeks.
  • hot_rod
    hot_rod Member Posts: 21,840
    Any idea what temperature fluid is being supplied. Dry, light systems like that may only need 90- 95° SWT. Give it the 5 day cure time and let it rip if it runs low temperature.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • modconwannabe
    modconwannabe Member Posts: 49
    Thanks for all your input and suggestions. The water temp is based on ODR so it has been all over place, like the weather (was 59 a couple days ago, is 29 now). It has been more than a week since install and 6 days since grout and seal so I am ready to give it a go. I do have an old FLIR so will keep tabs on temps and do cycling for the next day or so.
  • hot_rod
    hot_rod Member Posts: 21,840
    pretty much every time it comes on it will range from 68° or so to maybe 80° surface temperature. I think after the 5 day wait you should be able to start and run with out.

    The ODR should help avoid wide temperature swings, and with some tinkering may get you close to constant circulation.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • nibs
    nibs Member Posts: 503
    Caution costs less than repairs.
    Turn it on slowly.
    On my own thinslab & tile, is sometimes turn off a loop if working in the room, just to be more comfortable while I work.
    When I turn it back on I crack the valve a little bit for a couple of days.
    Call me chicken but I hate repairs.