Popping sound from Fiberock over concrete

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Greg Jones

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Hi,
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 sheets on the floor on top of ProLite - the manufacturer of ProLite says can be laid up to 3/4 inch thick. So the ProLite dded 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 fiberock 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 loud popping sound. They do not believe the ProLite is making the sound because they feel that it would be a crunchy, gravel sound, not a single pop. But they seem unsure.
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 coming from the fiberock.
Thanks!
 

Ernesto

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Thats a tough call. To find out I would cut out a section where it pops to determine the issue. Otherwise I'd say the fiberock isn't sticking to the mortar in some spots. It's a lot tougher laying backer board on a concrete slab vs on a wooden substrate where you can screw it down into the wood. They should have back coated the fiber rock before setting it to insure it sticks and eliminated any dusty surface.
 

Floorist

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Not a ceramic expert, but I don't think that anyone recommends installing fiberock over concrete since it is a decoupler. It could also be a flaw in the fiberock since it is made of recycled material. Carpet pad made from recycled material often pops from some of the material being hard plastic.
 

Greg Jones

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Thats a tough call. To find out I would cut out a section where it pops to determine the issue. Otherwise I'd say the fiberock isn't sticking to the mortar in some spots. It's a lot tougher laying backer board on a concrete slab vs on a wooden substrate where you can screw it down into the wood. They should have back coated the fiber rock before setting it to insure it sticks and eliminated any dusty surface.
They tested bending a Fiberock board until it broke and it was totally silent, no sound at all. So I don't know if the Fiberock could be making the noise. There are definitely hollow spots under the Fiberock. They said the leveling system pulls the boards up so it increases hollow spots, but that is generally not a problem with tile, but maybe because the Fiberock flexes, it's a different story. Do you think it's possible that the leveling spacers that were used are making the noise? Their plan now is to pour some very strong glue into the gaps between the boards so the spacers can't move.
 

Floorist

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If the fiberock was properly installed, there would be NO hollow spots under it. That is the purpose of the thinset underneath. I would think that the hollow spots are related to the noise. Sounds like installer error.
 

Ernesto

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If the fiberock was properly installed, there would be NO hollow spots under it. That is the purpose of the thinset underneath. I would think that the hollow spots are related to the noise. Sounds like installer error.
Right, should be no movement. I wonder what size trowel they used.
They tested bending a Fiberock board until it broke and it was totally silent, no sound at all. So I don't know if the Fiberock could be making the noise. There are definitely hollow spots under the Fiberock. They said the leveling system pulls the boards up so it increases hollow spots, but that is generally not a problem with tile, but maybe because the Fiberock flexes, it's a different story. Do you think it's possible that the leveling spacers that were used are making the noise? Their plan now is to pour some very strong glue into the gaps between the boards so the spacers can't move.
If ya got enough mud underneath the levelers then there should be no hollow spots.
 

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