Fiberock underlayment on slab making popping sound

Discussion in 'Floor Preparation' started by Greg Jones, Sep 25, 2019.

  1. Greg Jones

    Greg Jones Member

    I purchased engineered wood flooring at my local flooring store and they subcontracted the installation. My bedroom's concrete (slab) floor is about 2 inches lower than the marble tile in the hallway that leads to my bedroom. In order to raise the bedroom floor to make a less extreme transition, the contractor decided to lay fiberock tile backer board on the floor on top of a high-end type of thinset-type of material (I forgot the name of it) that the manufacturer says can be laid up to 3/4 inch thick. So the heavy duty thinset-type of material added 3/4 inch, the fiberock added 1/2 inch, and the engineered wood, after it is laid down will add 1/2 inch, bringing the height difference between the 2 rooms to only 1/4 inch.
    So they laid down the fiberock a couple of weeks ago (there was a delay on the wood installation) and they used a wedge/spacer leveling system to minimize any lippage. Now, when I walk on the fiberock, it sometimes randomly makes a very loud pop/snap sound, almost like bubble wrap or popcorn popping. Not a bunch of pops at once but just one loud snap/pop/crack sound. And I usually can't replicate it if I step in the same spot twice. But hours later I can sometimes make it pop again in the same spot.
    The flooring store and the contractor can't figure out the cause of the noise. They screwed down some of the fiberock using tapcon screws and the floor still pops randomly when walking on the boards. At this point, they are running out of ideas and are thinking that the remnants of the plastic spacers from the wedge leveling system are somehow rubbing in between the fiberock boards and the slight movement from walking on the fiberock snags the leveling spacer and it is making the popping sound.
    That seems far fetched to me, but I guess they could be right. Any ideas what can cause this kind of noise? We obviously don't want to glue down the engineered wood until we eliminate the popping sound.
  2. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Based on the installation instructions (attached) and your comment above I'd say they didn't follow the installation instructions if they used spacers in between the boards.

    Per the installation instructions:

    "...Butt panel edges and ends lightly together. =A maximum 1/32" gap is allowed."

    I've never seen any type of wedge spacer system that is 1/32" or smaller so they've allowed too much gap between the panels. It's very likely that what you've stated in your post is what is occurring regarding the remaining portion of the spacers but based upon what the panel manufacturer is saying in their installation instructions, they should have never used a spacer to begin with.

    Sounds like somebody has got a lot of demo work ahead of them.
  3. Jim McClain

    Jim McClain TFP Owner/Founder Administrator

    This is what it says pretty plainly in the Fiberock Installation Guide: "Do not use USG Fiberock panels over concrete subfloors or over cushionbacked vinyl." Even if an installer felt it was an acceptable option, the slab would have to be prepared so that the thinset material would be able to bond to the slab. Spreading it directly over a finished concrete slab would not be a good idea. And not using fasteners with large enough heads every 8" length and width of the panel within the stated working time of the thinset could cause even more problems.

    It doesn't appear that your engineered hardwood installers were qualified to work with Fiberock. There are other ways to raise the floor to the level you needed (and without that quarter-inch lip). It's too bad your installers don't know how to do that.
    • Agree Agree x 2
  4. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Thanks for catching that Jim. I missed that little blurb as I was reading the panel installation section.

    What Jim's said is obviously the much bigger issue vs. what I posted.
    • Like Like x 1
  5. Greg Jones

    Greg Jones Member

    Thank you. Can you recommend the best way to raise the floor? Hopefully it's not very expensive.
    I understand that this is not an approved use of Fiberock but the installer says he does this method all the time without issues. He said the only thing he did different this time was using the wedge leveling system/spacers in order to reduce the floor prep.
  6. Jim McClain

    Jim McClain TFP Owner/Founder Administrator

    I can't, mostly due to lack of experience and the introduction or improvements made in self leveling cement and other products in the 13 years since my retirement. But there are some excellent and qualified pros here at TFP and I hope they will add to this discussion.
  7. Commercial Floor Rep

    Commercial Floor Rep I Support TFP Published

    Once the current situation you have is removed back down to the slab, the simplest thing to do is use a self-leveling cementitious underlayment to bring the floor up. There are several manufacturers that have products designed for this type of application. Uzin, Mapei, and Ardex are some of the most popular manufacturers of these types of products. Each of these companies have multiple products at multiple price points with slightly different characteristics.

    Some products work quickly (16 hours minimum cure time for something like this is considered quick) but the speed comes with a higher price tag generally. Other products require a bit longer curing time (2-3 days vs. 16 hours) but these are generally less expensive. Within each one of these characteristics each manufacturer will also have products that can only be poured up to say 1" thick per pour while other products will be able to do the hole thickness in 1 shot.

    Based on your original message it sounds like you've got a 1/2" thick engineered wood product so to get to level with the marble floor you would need to level 1 1/2" if I'm understanding correctly. To do a rough calculation on about how much self-leveler you will need you can calculate about 1 lb. of leveler per square foot at 1/8" thickness. That being said you're roughly talking about 12 lbs. of self-leveler per sq foot of area at 1 1/2" thickness.

    Depending on the manufacturer and the product selected you may have the option to utilize clean pea gravel mixed into the product to prevent having to purchase so much leveler and save costs. The manufacturers will each have specific recommendations on how much (what ratio) this can be added if it's acceptable for the product that is selected.

    Each manufacturer will also have recommendations as to whether or not a primer is needed prior to the self-leveler being poured. Coverages and specific installation instructions will vary across products.

    A decent self-leveler from a supplier will range from about $20.00 per bag (generally 50# bags) to about $55.00 per bag for the faster products with more "bells and whistles".

    Labor will depend upon your local market and can vary drastically based upon the skill level of the installer and their comfort level with self-leveling.

    Hope that at least helps with a possible solution for your situation.
    • Agree Agree x 1
    • Informative Informative x 1
  8. Dan Schultz

    Dan Schultz Certified Wood Floor Inspector Charter Member

    I hear guys say they've been doing this or that for years, blah, blah, blah. They have just been doing it wrong for years.
    • Like Like x 1
  9. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Moisture from thinset then hardwood on top. There was all sorts of discussion on how to save money, I get it.

    Fiberrock I’ll have to look up. So he used medium bed mortar maybe Mapei Lowe’s or custom Home Depot. Possibly Ardex. There’s just so many things that can go wrong that’s why it’s not recommended. Even leveler is tricky if not followed by more than experienced but trained personnel.

    Some would’ve put a sleeper system down and used naildown hardwood. If it were a good hardwood installer.

    I assume fiberock is like Hardiboard which gets fastened to wood subfloor by screws/galv nails. So not exactly how much wood content is in those products probably why not for slab cause it’ll expand from moisture. The thinset under it is just to fill voids after fastening.

    Fiberrock, Gypsum based cellulose product, of course, it’s in their name. In this case it’s used as “filler” material.

    This weeks Bill is around 9k$ for two jobs(Failed) that never were approved by the TCNA, sheet vinyl paper backing glued down, then thinset and tile. But I’m not complaining.
    Last edited: Sep 26, 2019

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