Springy floorboards over concrete

Q: I installed an engineered bamboo floor. There are several areas of springy floorboards, where either there is unevenness in the concrete floor or the adhesive has dried out. The result is boards that are loose and springy.

What are my alternatives?

A: Perhaps you could drill a small hole in the area that is moving and inject an adhesive.

Similar Q: Just recently installed Brazilian cherry (tongue and groove) hardwood flooring on a concrete slab. Home is l5 years old. Installers also glued it down as well. There are about 4 areas where it is soft and spongy when I walk on it. It’s been down now about 2 months. What has gone wrong?

A: If this was installed directly on concrete, glued only without nails it could be there was a bit of a dip in the concrete so the adhesive wasn’t able to grab the underside of the flooring. I don’t think I would ever attempt an installation of this type with solid wood. There are injectable adhesives that can be used. You have to drill one or several tiny holes and insert tip or tiny hose. The adhesive will expand, filling the cavity and grabbing the underside of the planks. Hope that helps.

Similar Q: We had a couple of spongy spots in our newly installed glued down bamboo floor. We had the flooring and subfloor removed and found the floor has a couple of spots where it is uneven by 1/16-1/8″. What can we do for this and should the contractor have seen this during installation and just added more glue to the area? Would he have seen this during installation and should he have stopped the installation?

A: 1/16 to 1/8 isn’t much variation. Perhaps if he rolled the floor he may have just missed this spot and didn’t get grab with the adhesive. There are injectable adhesives. You drill a tiny hole and insert a tiny tube. The adhesive will expand under the floor and fill the void. I do believe Bostick makes a product like this.

Related Q: We laid engineered wood floors on our concrete slab, only to find an area that dipped about an inch after the glue dried. The floor flexes when the spot is stepped on. Unfortunately, the spot is in a high traffic area. Is there a filler that can be injected below the wood floors to fill the cavity?

A: There are indeed injectable adhesives, one being made by Bostik-Findley. I think the idea is to drill a tiny hole to accommodate the long tip of the injector and squeeze in the adhesive. It will expand, filling the void, gripping both the concrete and bottom of the floor. I would suggest applying painters tape around the hole in case the adhesive expands through the pilot hole and gets onto the floor surface. It should do the trick.

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