Hollow spot in floating floor

Q: I wondered if you could suggest a fix please, for our new kitchen. The original floor was concrete, and this had levelling compound put on top, a floor fitters request. All looked okay, but there is a hollow spot in floating floor (now it’s all fitted where it creaks when you step on it, you can see the wood dip when you apply weight). Obviously it’s a little hollow in that area. The floor is floating engineered wood, sitting on a moisture barrier/underlay.

As the floor is not glued down, can I still inject adhesive though the board and wait for it to cure effectively “filling” the hollow rather than gluing it down? The hollow spot is only a few boards in, so I may do it from side rather than drill down. Or is there a better way? (The fitter is no longer with us, floor is a year old now..)

A: I think you’ve got the right idea for an easy fix. I believe Bostich has such an ‘injectable’ adhesive. I’ve never used it but I would think it expands as it cures, thus filling the void. So, if you can do this without drilling a hole, all the better.

Similar Q: Why are there air bubbles in the glue that I’m using for our bamboo floor? I recently installed my living room and now when you walk on it, you hear popping.

A: It’s possible that you didn’t get complete grab of the adhesive between the sub floor and the bamboo. This could be caused by something as simple as a slight depression in the sub floor. It’s probably best with a glue down floor to go over the floor with a weighted roller as you work. If there are hollow spots here and there you can use an adhesive syringe after drilling a tiny hole. This will expand in the cavity under the floor and stop the movement. I believe companies such as Bostik Findley make products like this.

Related Q: We just installed engineered maple over concrete slab. There are some areas of “hollow” sounds, when you knock on boards, but no sounds when walking on floor. What do you think causes the uneven “hollow” sounds?

A: A possible small dip in the concrete and perhaps poor grab of the adhesive in those areas. Was the floor rolled with a weighted roller when installed?

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